Zone 2 training: impact on longevity and mitochondrial function, how to dose frequency and duration, and more | Iñigo San-Millán, Ph.D. (#201 rebroadcast)

This episode delves into the specifics of Zone 2 training—a type of low-intensity exercise beneficial for mitochondrial health and longevity.

1. Zone 2 Training Defined: Zone 2 training involves exercising at an intensity where fat is primarily used for fuel, promoting mitochondrial efficiency and health.
2. Benefits for Longevity: Regular Zone 2 exercise can enhance longevity by improving metabolic health and increasing insulin sensitivity.
3. Application for Athletes: Athletes, particularly endurance ones, can significantly benefit from Zone 2 training by improving their energy utilization and recovery times.
4. Measurement and Monitoring: Accurately measuring and staying within Zone 2 involves monitoring heart rate and lactate levels to ensure the exercise remains in the low-intensity threshold.
5. Practical Implementation: Dr. San-Millán suggests ways to integrate Zone 2 training into regular workouts, emphasizing consistency and gradual progression.

1: Introduction to Zone 2

Explores the fundamental concepts of Zone 2 training, its importance for mitochondrial function, and its relevance to overall health. Peter Attia: "Zone 2 training is crucial for enhancing metabolic health and longevity."

2: Mechanisms and Benefits

Detailed discussion on how Zone 2 training enhances fat oxidation and improves metabolic flexibility. Iñigo San-Millán: "It's not just about burning calories; it's about improving the quality of your metabolic health."

3: Implementing Zone 2 Training

Practical advice on how to effectively integrate Zone 2 training into a fitness regime. Iñigo San-Millán: "Start slowly, monitor your physiological responses, and gradually increase the duration."

• Start with Assessment: Begin with a professional assessment to determine your current fitness level and Zone 2 threshold.
• Consistency is Key: Incorporate Zone 2 training sessions several times a week to reap long-term benefits.
• Monitor Progress: Use heart rate monitors and lactate threshold tests to stay within your Zone 2 during workouts.
• Mix Intensities: Combine high-intensity training with Zone 2 sessions to optimize fitness and recovery.
• Listen to Your Body: Adjust the intensity and duration based on how you feel and your recovery status.

Iñigo San-Millán is an internationally renowned applied physiologist and a previous guest on The Drive. His research and clinical work focuses on exercise-related metabolism, metabolic health, diabetes, cancer metabolism, nutrition, sports performance, and critical care. In this episode, Iñigo describes how his work with Tour de France winner Tadej Pogačar has provided insights into the amazing potential of elite athletes from a performance and metabolic perspective. He speaks specifically about lactate levels, fat oxidation, how carbohydrates in food can affect our lactate and how equal lactate outputs between an athlete and a metabolically unhealthy individual can mean different things. Next, he discusses how Zone 2 training boosts mitochondrial function and impacts longevity. He explains the different metrics for assessing one’s Zone 2 threshold and describes the optimal dose, frequency, duration, and type of exercise for Zone 2. Additionally, he offers his thoughts on how to incorporate high intensity training (Zone 5) to optimize health, as well as the potential of metformin and NAD to boost mitochondrial health. Finally, he discusses insights he’s gathered from studying the mitochondria of long COVID patients in the ICU.

People

Peter Attia, Iñigo San-Millán

Guest Name(s):

Iñigo San-Millán, Ph.D.

Content Warnings:

None

Peter Attia
Hey everyone, welcome to the Drive podcast. I'm your host, Peter Attia. This podcast, my website, and my weekly newsletter all focus on the goal of translating the science of longevity into something accessible for everyone. Our goal is to provide the best content in health and wellness, and we've established a great team of analysts to make this happen. It is extremely important, important to me to provide all of this content without relying on paid ads to do this.

Our work is made entirely possible by our members, and in return we offer exclusive member only content and benefits above and beyond what is available for free. If you want to take your knowledge of this space to the next level, it's our goal to ensure members get back much more than the price of a subscription. If you want to learn more about the benefits of our premium membership, head over to peterattiamd.com subscribe welcome to a special episode of the Drive. For this week's episode, we want to rebroadcast one of our most popular episodes, which is the second conversation I had with Inigo San Milan in March of 2022, which was a deep dive into all things pertaining to zone two exercise. Inigo is an internationally renowned applied physiologist and assistant professor at the University of Colorado School of Medicine.

His research focuses on exercise related metabolism, metabolic health, diabetes, and cancer. In this conversation, we talk about Inigo's work with two time Tour de France champion Teddy Pogacher, looking at the type of training that he does and what we can learn about training in cardiovascular physiology from the world's most elite performers. We talk about lactate and fat oxidation as it relates to cardiorespiratory training and how carbohydrates in our food can affect lactate, and we talk about what different lactate levels mean in the context of healthy versus unhealthy people. We get into very specific detail around zone two exercise, how to measure it how to know you're in zone two, what to do if you don't want to use a lactate meter how you can structure your training around it how to think about duration, timing and frequency. Talk about the importance and the compounding rate of improvement that can happen with zone two training, vo two max training, high intensity training, and how different exercises of this nature can improve your lifespan and health span.

This is a rather tour de force episode when it comes to zone two training, and obviously it's a term that many of you are very familiar with, but it's really great to go back to the source where we started talking about this with Inugo several years ago and then followed up again in 2022. So without further delay, please enjoy or potentially re enjoy my conversation with Inigo Sun Milan.

In you go. It is so great to be sitting down with you again. Last time, of course, we did this in person, but these days I've become too lazy to travel around and do podcasts in person, so do it by video. But that said, I really hope you can get out here to Austin so we can train together and do some cool ex fizz. And also, I need to get out there to sort of do some of the ex fizz stuff we've talked about.

But I almost don't know where to begin because there's so much stuff we talked about last time that we want to double click on this time. There's so much that has changed in the interval from when we spoke. Gosh, probably two years ago. A little over two years ago. I thought one place we could pick it up, something we didn't really talk about last time, was your work with Tadi Pogatcher.

Because of course, I don't think anybody knew who he was two and a half years ago. And of course now he is. I don't know. I mean, I think it's safe to say he has the potential to potentially go down as the greatest Tour de France cyclist of all time, given how young he is. Not to put that expectation out there, but to win the Tour at such a young age, to not just win the yellow jersey, but the white jersey, polka dot jersey repeatedly.

He looks like something of a different species almost. And I say that not in the way that people typically say those things of cyclists in a way that's suspicious of anything. So for the listeners who are not familiar with the Tour de France, not familiar with your work with the UAE team and your work with Tadi Pogachar, maybe give folks a little bit of an update as to what you've been doing in professional cycling over the past couple of years. First of all, thank you very much for having me here. It's an honor.

Inigo San-Milan
Really excited for this and I appreciate the opportunity. I had a lot of fun last time. Hopefully I have fun again. My work with Tade started in late 2018 when he signed up for the team. Yeah, I was introduced to him by our CEO, Janetti, and our general manager, Macin told me, hey, start working with this guy.

Peter Attia
And he was what, at the time? 19 maybe? Yeah, 19. He was 19 at the time. Since I turned 19.

Inigo San-Milan
In fact, I started to work with him right away. I realized he had potentially and I think, like a couple months earlier. No. Or later. I forgot when we had that podcast, I already told you about him.

Told her, like, we have a guy that has good potential. That was today. To put it in perspective, I mean, has good potential is one thing. To then go and do what he did would make that statement. The understatement of the century for folks who maybe don't follow cycling as closely.

Peter Attia
Right? Yeah, yeah. I mean, I try to be cautious. I don't usually say that. A lot of people who have good.

Potential, we talked about it over dinner that night. Yeah, yeah. When I say someone has good potential, I don't usually say that lightly of anybody. What did you see in him in 2018, 2019 that led you to believe that even amongst that class? Because professional cyclists, from a physiologic standpoint, are all very special individuals.

What did you see in him that made you think he has potential in your understated way? The physiological testing we started doing, right off the bat, I saw, like, amazing capabilities, ability to clear lactate and to put out great amount of power for long periods of time. So when you say that, was it specifically his FTP that impressed you, or was it his, as you said, lactate clearance, was it shorter bursts of power that were higher than FTP, but the speed with which he could do, or the successive repeats that he could do? I mean, tell me some of the testing you were putting cyclists through and how he stood out. It's kind of like similar tests that I did to you.

Inigo San-Milan
And this is where I saw that at a given power output, his lactate levels, blood lactate levels were extremely low. And since I've been doing this specific protocol for 20 years with professional athletes, professional cyclists, in this specific case, that's where I have my cheat sheet, where I know I can categorize where people are. He was like, whoa. On the other side, way above almost everybody that I had tested, or around the same category. And for that age, that's what I saw.

Like, whoa. First of all, he is at a different category, and he's first year pro, pretty much a junior. And then that's where, like, I could see he could sustain high amount of power with very low lactate compared to the rest. And then throughout the trainings, we use Trainingpix, the software looking at trainingpeaks, that's where I would see his different abilities to sustain a given power output for the whole day or for a specific effort, a glycolytic effort on a client would see the power output that he would be putting out. And so altogether, then I saw his trainability, how easy he would get, the concepts, how easy he would comfortable with the training, how easy he would recover.

I like the feedback. I talk to him once, twice a day over WhatsApp to the feedback. I know very well when a hard week is, or what a heart week is. And when you see this kid telling you, pretty good, I'm recovering very well, when other ones are telling you, woof. I had to take it a little bit easier today because I couldn't do this effort.

And we're talking about high level pros, and you see this kid telling you like, yeah, there's no problem. That's where you start putting together things. And also around the same time, with my two colleagues at the university, Angelo D'Alessandro and Travis Nenkov, we started developing a platform for metabolomics, where we can look at hundreds, if not thousands of metabolites in the human body. And we did it, the tour of California in 2019, which was, like, around April. That's where he wanted, and that's where, when we analyze all his metabolites, and we did already at the training camp in January 2018, and we already saw, wow, this guy has different metabolites at the glycolytic level, oxidative level, recovery level, and we confirmed that at the tour of California.

And this is where putting all together. Yeah, this guy is different. So going back to what you said about Lactate, I assume that one of the data points that is most telling of a cyclist is if you plot on the x axis, watts per kilo, and on the y axis, lactate production, I mean, that might be one of the most telling graphs you could generate to predict success in the tour, correct? Absolutely. You see a normal tempo climbing in the Tour de France tempo.

That is the whole peloton going up. It's got to be four. Yeah. As if I was about to say, wow, I was going to say four and a half. Okay, so, wow, the whole peloton is going up at five watts per kilo.

Yeah, something like that. And that's what you see. Like someone at that intensity might have already six millimoles. So you can tell it's going to be very tasking and others might have one resting levels. It really, really predicts performance.

In fact, when we go to these training camps, I'm going to go next week for the first training camp of the year with the team. We do this physiological testing, and I do this protocol and I get this data. So right away, I tell the team managers, this guy is way above the rest. These three guys are really, really good immediately behind it. These two guys are in the third level, and then we have all these guys that they're like really, really bad form, and it pretty much works.

Then we do different racing simulation, and they tell it, boom, right away. This is how it is. So this is why it's very predictive. And the same thing, too. Moving into the season, you see, okay, all these three guys are going to be at a very good level when we start the season.

This guy, we thought that he was going to be a very good level. He's not there at all when the season starts, you see that it reflects very well what's going to happen. Yeah, that's one of the things about cycling that I really love. I don't know if you saw, but I interviewed Lance Armstrong back in, oh, gosh, probably back in June, or maybe it came out in September. But one of the things that we talked about was both on and off EPO or blood transfusions.

Peter Attia
You sort of knew where you stood before the race based on your FTP in watts per kilo. He talked about when he was off EPO, he could hold 450 watts for 30 minutes. So that would be slightly above FTP at 70. I think he was 70 to 75 kilos, but it was in the ballpark of six watts per kilo. And then, of course, on EPO, it was 7.1 watts per kilo.

A huge difference. But you knew that number going in, and you sort of knew only the GC contenders could do that. I think that's the thing that a lot of people don't understand about cycling, which is there's relatively few moments in the tour when you need to sustain that level, but they always occur at the most important, strategic times. And that's sort of where the race is won and lost, because the race is won and lost by minutes. How many hours does it take to complete the tour?

100 hours or something? Average about four and a half, 5 hours a day. Yeah, so something like that, yeah. It's about a hundred hour race, and yet the difference between the first, 2nd, 3rd guy will be, in some cases seconds, in some cases a few minutes. For someone to win by five minutes is considered a blowout.

And so what it really tells you is that there are a handful of minutes in that race, there are a handful of climbs and time trials that set apart the winners from everybody else. And to me, that's one of the beautiful things about cycling physiology, is you have these metrics, and now I think it's not just FTP, it's watts per kilo at lactate production. So it gets even more into the critical physiology of recovery. In fact, we use these metrics a lot for the competition, and we did it this year. France, knowing the power output that he could sustain for, as you very well said, for a specific times and clients, we knew his capabilities.

Inigo San-Milan
And one of the things that we knew was that in the Alps, he was at a very, very high level. That famous stage where he broke away in Col du Rome, 35 finish line. We are seeing not only his data, but we see by knowing our writers data, you can also guess the other writers data, too. It's not rocket science. So we knew that he was at a very high level and discussing the ticks, because it's part of the thing that we do.

We observe the data that we have, the data that we think the other ones have, and we structure a strategy for the next day. And, hey, does he have the legs to attack? Should be holding back, or what should we do? And clearly it was like, well, tomorrow, if he attacks 35 finish line, he's going to get there with three minutes, because the other guys, they're not at that level. Why wait to the end of the tour when we can try to solve the situation?

So we knew his capabilities very well. And discussing this with him and the manager, yeah, that was the strategy. First, test the legs. And like, if you had, in fact, good legs, boom, go for it. And that's exactly what he did.

Peter Attia
Now, how much of that are you going to determine after a night of sleep, where you say, we're going to look at his resting lactate first thing in the morning, we're going to look at his heart rate overnight. We're going to look at his heart rate variability overnight. So in addition to the subjective, for example, how he felt during the previous days attacks, coupled with some of that objective data, does that partially formulate the strategy also? Or is it mostly based on historical data from training where you say, I know that when he's at this many watts per kilo for this many minutes, he has the capacity to recover. The latter, where we have all that physiological data and the trends, what we see at this level, these guys, they're so good at knowing their feelings.

Inigo San-Milan
Sometimes it's just kind of how they wake up, you know, his capabilities. So if he wakes up fresh like a baby boom, then you're ready. And sometimes, yeah, it's just we try not to focus on many other metrics that they, because we have already things. And sometimes Harry variability, that might not be very precise, and we don't want to put some ideas in the head. And in fact, speaking with him, you know, and I'm not going to mention any brand or anything, but looking at Harry variability some days and say, like, look, today he told me that I was fatigued, that algorithm, and I went out there and beat my record on the climbs.

Obviously, I'm not fatigued. There are days it tells you you're in top form, and I feel a little more fatigued. So this is what these algorithms, we need to be careful sometimes and might work with maybe general population, but with this type of athletes at this level, I really feel that it's better once you have all the work done, you know, their capabilities. Like, are you ready to go? It's like a top performer at a theater.

You have worked very hard. Now it's up to, like, are you ready to go? Do you have a good night's lead? Are you ready to perform? And a good performer would say, yes, I'm ready to go.

Peter Attia
I agree with you completely. Even for me, and I'm not a top level anything. I have not found the predictors of readiness to be very accurate or to necessarily reflect how well I'm going to perform. I've had amazing performances. By performances, I mean workouts.

That's the only metric I'm performing in. I've had amazing workouts when my prediction was that it would not be good. And I've also had the prediction saying, you're on top of the world, and I've not performed well. So I wish I could say with more clarity what the frequency of those deviations or discordances are. But I can agree that putting the wrong idea in somebody's head when there's nothing you can do about it, I mean, that's the other thing, too.

It's sort of like, at best, if it was perfectly accurate, it would be great, because you could say, look, today, maybe we shouldn't attack today. It's damage control day. One of the things I want to ask you about here, and you've spoken about this publicly, so it might be that you're just going to restate the views that you've shared publicly. But I've always felt that now that we have such great transparency from that high octane era of the maximum, probably cheating in cycling, which, in my view, is kind of that two decades of the nineties and two thousands, we pretty much know now what kind of numbers cyclists were putting out when they were being assisted by EPO and blood transfusions. And we sort of know that the best of the best, we're able to put out somewhere between about 6.8 and 7.1 watts per kilo at FTP.

We also know today that cyclists are not doing that. Those numbers are nowhere to be found in the peloton. Now, that's information you and I share confidentially. That's not public knowledge, but I know it, you know it, and anyone coaching people at that level know that nobody's putting out 7.1 watts per kilo. You don't need to be at 7.1 watts per kilo to win the tour today.

You could probably win the tour today at 6.1 watts per kilo. Do you think that making that data public would put to rest a lot of the criticisms that say they've just found new ways to cheat, but it's still basically a dirty sport, because when you look at the data objectively, it would be very hard to say that today, based on what we know from the era when drug use was rampant. No, I think you make a very good point. It frustrates me when people think that they're doing seven watts per kilogram, 7.2, and then you have the real data from the day, and this is way lower. The short climbs, where they would do maybe 7.2, now they're doing 6.3, maybe, and the longer climbs they were doing 5.55.8.

Inigo San-Milan
It frustrates me because I see this data, goshen, I wish I could just, boom, release it. I have absolutely no problem with that. We debated it with the team. We're keeping all this. At the end of the day, people can figure that out.

And some people, what I see on Internet, as you can see, the weight of the cyclist, the grade of the crane when it starts, the time, and the wind, you can be very accurate at knowing that. And I see some people, they're quite accurate, Internet. But I see other ones are all over the map. Did the formula in 7.2. My gosh, I wish I could show him, hey, this is the real data that we see in two points.

There is like, one, it's private data that the team considers, like, not releasing. That's team policy. But the other one, too, is like, even if you release that data, there are always going to be people that are not going to believe you. Or they might say, oh, they probably altering the data, or they're tricking it somehow or putting more weight to the data so it looks like there's less power output. I don't know if it's.

It'll be an endless fight. I don't have the answer. I just have that frustration that I wish that I could really show the data and people can see it. There's always going to be someone who's not going to believe it and going to make a lot of noise out of that. That's the other thing, too, is like other teams and other writers are releasing their data.

So by releasing their data, you can see pretty much where boccaccio is. Okay, if it's a minute ahead or 30 minutes sequence, or sometimes with the same time, you can see, whoa, whatever the writer has done and has entered into Bogachar's group, or 30 seconds later and has done 5.9, volatile is going to be in that neighborhood, not going to be seven with 30 seconds ahead. In the spirit of releasing data, the other thing it would potentially do, especially if you could see it in real time. I don't know if you watch Formula one, but one of the things about Formula One that I think the sport has been able to do because of the advances in technology, is make more of the data available to the viewer. If you're watching Lewis Hamilton driving a lap, you see what he sees.

Peter Attia
Now, you can see, and it's not the end of the world data, but you see his speed, you see what gear he's in. You see the difference between throttle and brake pressure. They could show even more data, certainly, and someone who drives would appreciate it if you really saw brake bias and if you saw brake pressure and lockup and things like that. And you can hear the drivers speaking with their race engineers. So it basically allows you to come more and more into what they're doing.

This year they introduced a new camera angle, which is what the driver sees. And I think it's fantastic because historically, you see above them and it looks so smooth, but that's not at all what it feels like to be in a race car. So now they just literally put like a camera at their shoulder, and now you see how restrictive the halo is. You see the bumps, and it looks a lot faster. You know, I've had this discussion with a number of people, which is if you could show the same sort of information in cycling, if every time the camera went over to a cyclist, you saw their heart rate, their watts per kilo, their speed, all of these other things, and you could hear some of the communications back and forth with their teams.

Yes, that changes the sport strategically. Now, you have to be careful what you say on the radio, but it also allows you to see the human element of this sport a little bit more. Do you think that will ever happen where you'll be able to flip on the Tour de France and you'll be able to actually see real time physiology? I would love it. It would be so much fun for the viewer.

Inigo San-Milan
And cycling has so many possibilities to engage people more and be fascinated by the physiology. And looking at these numbers, it's already, in a way, you see some cameras already installed in the front and the back. It's called velon. You can see really cool images when they're preparing a sprint that is like what feels inside. And you can see it's really scary sometimes you can appreciate how difficult it is to be at 40 miles an hour sprinting, or 35 miles an hour leading to a sprint, or in a.

Peter Attia
Descent at 60 or 70 miles an hour. 70 miles an hour descent. Exactly. And then you can see the power output in real time? I think it's a great step.

Inigo San-Milan
You don't see all the writers, but it's estimation only the writers will wear that villain or the vellum decides to do that. And I think that they're still not doing that with all the top contenders, but I think it's a first step and obviously, having spoken with them, but maybe it's like, hey, let's see what's the feedback? And I think that people are loving it. I would expect that will increase. I would love at some point, and as you know very well in the world of biosensors, going to revolutionize sports, where we're going to be able to see so many different parameters of athletes in real time.

Yeah. Imagine you could see lactate and glucose in real time. Absolutely. Which, of course, is technologically feasible already. Exactly.

Yeah, I think that would love for all sports, too. Imagine you can see an NBA basketball game and see that the lactator of LeBron James compared to the other ones. I mean, I would love to see that as a spectator, and I hope that someday we were able to see these parameters. So, last thing on the tour, talk to me about Ventu this year. That was a tough stage.

Peter Attia
It looked like his toughest stage. Is that a fair assessment? Yes, probably. And what's amazing, I think, is the poise on that stage. It's hard to tell if he was really struggling on the ascent of Van Tu Orlando or he was just deciding strategically, I'm going to conserve a little bit of energy here.

What was your take on that? Or what can you say about that? It was a very difficult climb and a very long climb. Tade, his mentality is wired like a champion. When someone goes and they were full gas in the last part, Vinge got attacked.

Inigo San-Milan
Tade knew that this is not going to be the top of Bon Vantoo, is not going to be the end of the stage. There's a very, very long descent, and I have some partners with me that they can help me out. I'm not going to panic at all, but I'm not going to also waste a lot of energy. He also had a big gap. A whole different thing would have been if he had 20 seconds, but having a big gap and knowing that you have a big descent and how calm he is, that's one thing that is a very important strategy.

This is what happened. This reminds me, in a way what happened the first year that he was pro, when he was 19 at the Tour of California. It was the previous stage before Bear Lake, top Mountain in the tour of California, where it's going to be decided. So the day before, two cyclists, George Bennett and Yigita, attacked in a short but very steep climb, and there were only like twelve riders left and Yigita and Bennett attacked. Then there was like a descent and a long highway all the way to the finish line.

So there was plenty of time to catch him up. Tade didn't follow them up. Another writer would have just followed their wheel. And tada decided, no, I'm not going to follow them. We have time and I'm going to take the chance because I'm confident for tomorrow.

And when I asked him, as soon as he crossed the finish line, I asked him, are you ok? Why you didn't follow their attack? He said, well, I just, I wanted to know who is going to be good tomorrow. So I know those two guys are going to be good tomorrow, but I wanted to take my time and see the other ten guys, how they're breathing, what's their body language, take my time to observe, to start preparing my strategy for tomorrow. And in fact, that's what he did.

They were then caught up two, 3 finish line. So all those 1213 guys, whatever they were, they got together and the next day, in fact, he noticed those two guys attacked. He just followed them and he just eliminated one by one. That's how this guy thinks. No panic, plenty of time.

Today I have a good gap in the GC. Why am I going to go full gas when I know that he's going to go full gas and he might lose energy for tomorrow? Because he might pay for this at this time of the Tour de France, and we have plenty of time to catch him up. So that's kind of the strategy that he had. How much time does someone like Tadi spend in zone two, which we're going to talk a lot about, and let's do it more as percentage of training time because I think absolute numbers will be very large given that that's his job.

Peter Attia
But when you think about the percentage of time he spends in that energy zone, how does it change over the course of the year? So presumably during the winter months, a greater amount of his time would be spent there as he's base building right before a race, when he's kind of sharpening, maybe lessen what would be the range of time or percent rather. Yeah, yeah, you're right. When we talk about percentage, I like to put it this way, more like a percentage of days dedicated to cultivate that energy system. Obviously, if you put in just every single minute together, the majority is going to be that.

Inigo San-Milan
But I would say more in days. In the winter months might be about 80%, 70% to 80% of the days. As the season gets closer, he starts increasing more intensity. Days and sessions when the start of the season is racing and you have. It depends.

You might have one stage race of five, seven days, and then you have five day block or one week to recover and then you have the next stage rate. So in that week, we do a lot of recovery. We might do some sessions here and there, and then after a few blocks of races, that's where you have another long time to train, period. To train. Go to altitude towards the Tour de France or towards the next goal.

And that's where you may revisit these different energy systems and train specifically, we alternate, and each energy system has a time in the year in the calendar, what is built in order to try to achieve what we want. So let's remind people now, I've put out a few posts on social overdose, gosh, the past year and even in the past little while, and anytime I'm talking about zone two, it's really one of the topics that generates the most curiosity, the most inquiry from people. I think people really intuitively kind of resonate with this. And then of course, a million questions follow because there's so much minutiae and detail around it and a lot of that we're going to cover today. But let's start from a place of maybe someone hasn't heard the first podcast where we go through some of the semantics of this, define zone two.

From my point of view, it is the exercise intensity. At the one you are stressing the mitochondria and oxidative capacity to the most. This is where you're recruiting mainly type one muscle fibers. This is where you are mobilizing the highest amount of fat, both from lipolysis, from adipose tissue, as well from fat oxidation inside the mitochondria. This is also where you stimulate all those bioenergetics, which is oxidative phosphorylation.

This is where you burn both the fat inside a mitochondria as well as the glucose inside the mitochondria. There's not a very high glycolytic flux that it's going to be transformed into pyruvate and reduced to lactate, but that flux still is oxidized inside mitochondria. This is looking at from bioenergetics standpoint. This is what I would consider the zone two. And what I have seen is that throughout the years is that this is the exercise intensity that achieves or stimulates that mitochondrial function and fat oxidation and lactic cleanse capacity the most.

That's the other thing, too. This is where other things involving lactate. So lactate is a great fuel to the cells. In fact, it's probably the preferred fuel for the cells, for most cells in the body. This is a work that my colleague and mentor and friend George Brooks discovered.

Should have him someday in the podcast, because he's fascinating. I mean, I would not be surprised if someday soon we hear that he wins a Nobel prize. He's amazing. And every time I talk to him, I'm still alone a lot of things, and I've been translating a lot of his research. That's how I see that you have within the mitochondrial function, you see how lactate is oxidizing the mitochondria back to energy.

And that happens in those muscle fiber types, those muscle fiber types and the mitochondria. Those fiber types also develop these transporters, which are MCT one s, which are the ones transport lactate inside the cell and inside the mitochondria. So when you stimulate that training zone, you stimulate all these energy systems and the components that come with them. So let's talk about the different ways that one can go about estimating this based on the definition you've just given. It seems to me that the purest way to estimate this would be via indirect calorimetry, because that will actually tell us the fat oxidation.

Peter Attia
Is that a fair assessment? Yes, it's a very good assessment that usually correlates with the fat max. That's how we call it, too, right, that fat oxidation. And when you see there's, you start oxidizing fat and might increase in cases and gets to a point that is it maxed out, which is the fat max. And then it starts going down sharply as exercise intensity increases.

So let's tell people how that's measured. We do this with all of our patients, and I find it to be not that easy to explain because there's some physiology involved and there's some math involved. But let me try to see if I can explain this to folks. So you hook me up to an indirect calorimeter. So you're going to put a little plug on my nose.

You're going to put a mask over my nose and mouth. That mask has the ability to measure the amount of oxygen that I consume, because it has a sensor for o two. So it knows that the o two that's coming in is at 21%, the air is coming in at 21% o two. And whatever I exhale is the difference between that. So you can now tell how much o two was consumed, and you can have a similar sensor for carbon dioxide.

So you know how much carbon dioxide is produced. So it's very easy to measure consumed oxygen and produced carbon dioxide, provided you can completely isolate around the nose and the mouth as you hook a person up to some form of ergometer. Usually a bike, could be a treadmill, a rowing machine or something like that. You can increase the demand on the muscle, so you increase the wattage or the speed or the something. You then get out these numbers, vo two and vco two, which are what we just talked about.

So, consumption of oxygen, production of carbon dioxide. These numbers fit into a relatively straightforward linear equation called the weir equation, and it tells you three things. It tells you total energy consumption in kilocalories per minute. And then the ratio of vo two and vco two tell you how much of that energy is coming from fat oxidation and how much of it is glycolytic. So at any moment in time, you can look at a vco two and a Vo two, which are usually measured in liters per minute, and you can convert that into a total grams of fat oxidation and a total grams of glucose oxidation per minute.

And so you could then plot on the x axis, work or power, and on the y axis, you could plot fat oxidation again, describe for people what the shape of that curve looks like and what differentiates from the average human being. You explain it very well. Yeah, those are based on stoichiometric equations. The combustion of carbohydrates and fatty acids are done in the body. Already in the 1920s, Francis Benedict, one of the first ones, probably the first one who started to look into this at this level, obviously, we have evolved, do it in a more automatic way with these indirect color imageries.

Inigo San-Milan
Machines were called some metabolic cards. As exercise intensity increases, I mean, you need more oxygen, so your Vo two increases, and then you produce or give up more CO2. So this is kind of what it shows. When you're in a more lipolytic state, more fatty oxidation state, you still consume oxygen, but you do not produce as much CO2. When you are more into a more glycolytic state, which is higher exercise intensities.

When you're recruiting the type two muscle fibers and therefore using more glucose for energy purposes, you're going to consume more oxygen and you're going to produce more CO2. Plugging in all these numbers into these stoichiometric equations, it's going to give you that profile, the x and the y axis, and it's going to see what is the fat oxidation throughout rampant state. A ramp test. And this is where you're going to see elite athletes like bogaccar. They have an amazing fat oxidation capacity compared to other competitive athletes or recreationals or people with even type two diabetes or metabolic syndrome, or in a recent study we have published with COVID patients.

So it reflects, in a way, ultimately, what happens in your mitochondria and how the mitochondria oxidizes those fuels at different exercise intensities. So, for example, let's say at the intensity of 200 watts, elite athlete doesn't need to incur in that glycolytic capacity as much as someone who is not very well trained. So the elite athlete, they can still recruit slow twitch muscle fibers and rely a lot on fat to produce ATP because they have an amazing mitochondrial function and they're very efficient metabolically speaking. Therefore, they're going to be oxidizing a lot of fat. However, someone whose mitochondria are not working as well, whether you are like a recreational athlete or sedentary individual, or someone with type two diabetes, which is one of the hallmarks of the disease, that might have impairment or dysfunction, at 200 watts, you fully rely on glucose pretty much because you cannot sustain that effort with fat alone.

And this is what you're going to be seeing, this gas exchange, the cu two and the vo two, and you can just plot it into the equation, and it's going to give you all that, what I call metabolic map, where you see the fat oxidation, the carbohydrate oxidation, and then I plug in also the lactate. That's where everything comes together quite well. And you can then first, in an indirect way, calculate the mitochondrial function and metabolic flexibility, how flexible they are at using fats or carbohydrates, and also you can determine training zones. I've been using this methodology for 16 years, 17, something like that. I didn't think to ask you this earlier, but if you have it handy.

Peter Attia
Do you want to pull up a graph of what fat oxidation looks like versus power, so that people can see the difference between a highly trained individual, a reasonably trained individual, an untrained individual, and at the other end of that spectrum, somebody with type two diabetes. So this is from a publication that my colleague George Brooks and I published in 20 1317. This is the formula. And we have realized that this is flipped. So we need to work now with the editor to change it because the formula is flipped here in the methods.

Section, which is so funny, by the way. I like seeing that, I'm embarrassed to say. When we do this for our patients, we do it in two steps, which yields the same result. But we first calculate energy expenditure using the weir coefficients of 3.94 times vo two minus plus one point. I think it's one two times vco two.

And then we convert that to fat ox and carbohydrate oxidation using the ratio of vco two to vo two. And I never even thought to do what you've done here, which is so much more logical, which is combine them into a single equation for each. Well, we use what Frian observed already in 1983. And this is Friant's equation and it's been validated with tracers, stable isotope tracers, doubly labeled water. Yeah, and that's what it shows.

Inigo San-Milan
There's a very high correlation. Now, furthermore, in a study that we were going to be publishing soon, we have validated this fat oxidation and carbohydrate oxidation directly with mitochondrial respiration. So in muscle biopsies, we inject directly fatty acids, pyruvate, representative of carbohydrates, glutamine, representative of amino acids. And then we can see that there's a very high correlation between this indirect methodology to look at mitochondrial function and the direct methodology, which is through a muscle biopsy and injecting the substrate and see how it's oxidized. So these two graphs are really powerful.

Peter Attia
Let's talk about what the first graph is showing us. So both of these graphs, it's important to note I have the same x axis. In other words, the independent variable here is the workload in watts. That's the metric that matters in cycling, which is, I think, the easiest way to do this test. And so you're increasing wattage.

This is a progressive increase in workload. And what you're plotting on the y axis, your dependent variable here in the first graph, figure one, is blood lactate. What stands out to me is a couple of things. So you have the triangles represent metabolic syndrome. The squares represent a modestly trained athlete, and then the little diamonds represent a professional athlete.

The first thing that stands out to me, and we're going to talk about this later, so I'll put a little pin in this, is that the people with metabolic syndrome have a resting lactate. That's almost two millimole. Yes, we see already this. I think that it's going to become more and more as a biomarker, like resting blood glucose levels. What is your resting lactate?

Inigo San-Milan
You can see already in patients with type two diabetes or profound metabolic syndrome that, yeah, as you say, perfectly resting levels are in the neighborhood of, like, a 1.81.5 to even three. So one of the metrics that we've discussed at length, and we'll revisit it, of course, is using this lactate level of about two millimole as being that threshold. So once lactate exceeds two millimole, the individual is now escaping out of zone two, and they're actually now into zone three. So when you look at these data here, you can see that the individual with metabolic syndrome is basically tapping out zone two initially. So any incremental workload that is placed on them takes them right out of zone two.

Peter Attia
For all intents and purposes, by the time they're at 100 watts, they're already at the threshold of their zone two. Now, conversely, when you look at that medium trained or reasonably well trained individual, I think it's referred to as moderately active, healthy individuals, they start out with a lactate of about one, and it's not really until they hit about 175 watts that they pass that inflection point. And then when you look at the professional athletes, the professional endurance athletes specifically, they're starting out at a lactate level of 0.5 mmol, and they stay relatively flat until they hit about 300 watts, is when they finally cross over that threshold. Now, what's not captured here is that as you move from left to right, the athletes are getting lighter. So this graph if I'm going to be critical of it.

In you go. I would say it should be done in watts per kilo. And that would show a much starker difference between these and in our patients, when we benchmark them, we benchmark them in watts per kilo for this reason. So that you normalize by weight. And I'm certain you're absolutely right, and that's how we do it.

Inigo San-Milan
Also, one of the reviewers didn't allow us to use watts per kilogram. Clearly that reviewer was an idiot. So that's. I won't hold it against you, because the idiot reviewer. You know how it is in review papers.

You want to show something and eventually it's changed. And it's not exactly sometimes what you want to show, because otherwise they don't allow you to publish it. But anyways. But what's amazing here is that person with metabolic syndrome is probably about one watt per kilo. Easily one to 1.3 watts per kilo is their zone too.

Peter Attia
When you look at the modestly trained individual, they're about two watts per kilo. They probably weigh maybe two to 2.12.2 watts per kilo. That professional endurance athlete probably weighs in the neighborhood of 70 kilos. So they're in the ballpark of four watts per kilo. For our patients, Inigo, we set the aspiration at three watts per kilo.

So again, our patients aren't professional athletes. But we think that three watts per kilo would be kind of the elite level that we would want to. To see people. And then, of course, we stratify from there. Let's look at the lower figure, figure two, just beneath this.

So here we're looking at the same group of individuals. We have the same independent variable, which is work. But now we're calculating fat oxidation as a function of that work. So now your dependent variable is fat oxidation, which again, very easy to calculate via indirect calorimetry. Two things stand out again.

The first is the obvious, which is the fitter the individual, the higher their absolute capacity for fat oxidation. But something else stands out to me. In you go. And I have now seen this repeatedly across multiple data sets. Which is a fit individual actually increases fat oxidation to a local maxima before beginning that decline.

Whereas most mortals begin at a maximum and decline from there. Can you explain why that's happening? I agree. I see this all the time. I think that on one hand is how you start the protocol.

Inigo San-Milan
In this case, we start like Arbani. We start about one to 1.5 watts per kilogram. And that, obviously, for an elite athlete, is below resting level. So this is why they're very low, and they don't need to use much fat for energy purposes until you push them more. And that's when you get to, like, two.

2.533.5 watts per kilogram. Right. And again, this protocol comes originally from the work that I've been doing for 20 years, the same protocol with elite athletes. When you do the same protocol with other populations, especially people with metabolic syndrome or not very fit, and you start at 1.5 watts per kilogram, that might be too much. And I'm sure you have observed that if you start at 0.5 watts per kilogram, you might see a higher fat oxidation, and then you might see the same phenomenon.

So on one hand, is that protocol, but on the other hand, yeah, sure. Like 0.5 watts per kilogram, it's like nothing. It's close to resting levels, so it will take you for a long time. But that being said, I think that one of the things that we're doing with populations, for more clinical populations, is really starting at a very low level, even up to 50 watts or 25 watts sometimes. So we can establish these points, because if you start at two watts per kilogram or 1.5 watts per kilogram with someone with a significant metabolic dysregulation, you're going to miss the fat max.

Peter Attia
Yeah, I agree with you. We have been struggling to tune our algorithm to exactly that. I actually think, and I had this discussion with our team a week ago, which was, the physiologists who are doing this with our patients, are probably overcooking the people who are not fit during the warm up. So they do a warm up, and the warmup is actually too stressful, and it overcooks them. And then we're missing the true max fat.

The next thing I want to point out here, and let's just look at the fittest person, but it's true for all of them. But it's easiest to see here, fat max. So fat max ox. Right? So maximum fat oxidation is occurring earlier than lactate is two.

And that's true for all of them except for the metcin person, because it's so low. If you look at the moderately fit person, they're hitting maximum fat oxidation at about 130 watts, but they're hitting lactate of two at 175 watts in the upper figure. And the professional athlete is hitting an absolute fat oxidation maxima at a little shy of 250 watts, but they're hitting lactate of two closer to 300 watts. So I guess the question then becomes, you've already answered part of the question, which is we're really defining zone two as the place where maximum fat oxidation occurs. But I guess this would suggest that using a lactate level of two is maybe overestimating where that is.

And should we be using a lower level of lactate, such as 1.5 or something like that? This is what I've been learning all these years, is that the blood lactate levels might change between different groups. And it's everything related to the lactate kinetics and lactate oxidation in the mitochondria. So, for example, elite athletes, this was part of my doctorate thesis, and some of this that I never published it 20 something years ago. But the same blood lactate concentration does not correspond in an elite athlete, does not correspond necessarily to the same lactate concentration in a recreational athlete.

Inigo San-Milan
The metabolic stress. So, for example, two millimoles, two millimolar lactate in these elite athletes might be a higher metabolic stress than two millimoles in a metabolic patient. So this is why it would be very difficult. For example, you can have, let's say, two and a half millimoles. You can have a metabolic syndrome.

Patient exercising for a couple hours without a big deal. You try to do that with a professional athlete and they're going to be hurting. And in fact, one of the things that I observe is, like, I used four millimole, or millimolar, which is kind of that gold standard has been forever, like the lactate threshold, etcetera. If you put a world class athlete at four millimoles at the intensity in power output, that elicits four millimoles, and you put a recreational athlete at the power output, elicits also four millimoles, and you say, now go see who lasts the most. Intuitively, we're going to say, obviously, it's going to be the professional athlete.

It's the opposite. And this is the data that I saw 20 something years ago, the recreational athletes at the same blood lactic concentration would go about 30% longer periods of time. And that's because, metabolically, it's not as tasking. And the main reason is that the lactate that we see in the blood, it reflects the mitochondrial oxidation. So someone who has, obviously, when we're talking about high power output, when you need a lot of glycolysis to produce energy, you're going to produce lactate.

Lactate is the mandatory, obligatory byproduct, not waste product, but byproduct of glycolysis. So the higher the glycolysis, the higher the lactate. Now, that lactate has two routes, mainly, one is going from the fast twitch muscle fibers to the slow twitch muscle fibers, is the lactate shuttle that George Bush discovered and is oxidizing the mitochondria of those slow twitch muscle fibers. If you have a very good lactic clearance capacity, you're going to be oxidizing it very, very well for fuel. Therefore, you're not going to incur in the second step, which is exporting it to the blood.

When you have a poorer mitochondrial function, it's going to get to a point that that capacity is going to get saturated at a lower power output, and therefore you're going to be forced to export that to the blood. So that's why looking at blood lactates might not mean the same. I'm not saying that these parties are huge, by no means, but as you very well said, those two millimoles might not correspond in a lead athlete with a fat max, but might be more maybe towards 1.5, whereas maybe in someone with a more recreational or metabolic syndrome, it might correspond there. I don't know if it makes sense. It completely makes sense.

Peter Attia
And this is definitely the level of nuance I don't think we captured in the first podcast. And I want to now ask a more telling question specifically for the middle person here. So, the one that's called the moderately active individual, where again, we have a disparity. So, based on these data, the moderately fit individual hits a lactate of two millimole at 175 watts, but hits a max fat oxidation at, gosh, 125 watts. So it's a 50 watt difference.

So now the question for you is, when that person comes to you and says, in you go, I want to improve my metabolic function, I want to improve my mitochondrial performance, I want to improve my fuel, partitioning, my flexibility. All the things we talk about, are you going to train them as a zone two of 125 watts or as a zone two of 175 watts, as represented by these deltas? Normally, I would try to do something in the middle. Normally it might not coincide perfectly, but normally they do quite well. And another parameter, if you allow me, I can show you in this paper, when decided, we see individually the lactates and then we see the fat oxidation, but they will.

Inigo San-Milan
I decided to cross them over. This is what we saw in this graph over here. So this is where you see the lactate versus the fat oxidation in the elite athlete. And the r is 0.97. This is through Bonferroni.

Equation. So this is an average of all of them. And this is where you see the same pattern, the same graph for the moderately active. And this is also what you see in the person with metabolic syndrome. The correlations are very, very strong.

They're almost perfect. So this is what normally fat oxidation and lactate, they go together. So for people who are going to be listening to this, in you go and not able to see what we're seeing, can you describe the differences between these graphs? These are obviously showing the same data that we discussed earlier, but now we're using two y axes. So let's even just talk about it as looking at the elite athletes.

Peter Attia
So youre basically plotting the decline in fat oxidation, or in their case, the initial increase in fat oxidation, followed by a decline in fat oxidation. And on the same graph, you're showing the increase in lactate production. Again, both plotted to the same x axis of power. Does the cross point here indicate any significance? So they're crossing at about 325 watts.

Is there anything about that that means anything? I mean, to me, I think it's an artifact of the graph because it's really just a function of how you scale it, correct? Yes, exactly. I mean, it shows to me that, yeah, the crossover point for blood lactate and fat oxidation, very high. Obviously in the elite athletes, very far to the right.

And then of course, in the moderately fit people, it looks like it's closer to 100, maybe 80 watts. And in the unfit individual, it's about 125 watts in person with metabolic syndrome. If you started, and I'm sure you have seen this, but if you started with the metabolic syndrome, for example, at 25 watts, even in the recreational athlete, even earlier, you might see a similar pattern as you would see in the elite athlete, but a much lower watts. Obviously, we just did the same protocol for everybody just to show the concept, both fat oxidation and lactate go together. Also, when we look into, and I'm sorry, I should have gone to this directly, when we look into fat oxidation and carbohydrate oxidation, we see the same concept.

Inigo San-Milan
So we see as exercise intensity increases, you need to oxidize more carbohydrates. And then as exercise intensity increases, you might get to the fat max. And then in the moment you switch to the glycolytic fibers, you cannot use much fat for energy purposes. You see a sharp decline and eventually fat oxidation disappears. And it's all full glycolytic and the same pattern we see in the rest of populations with also very high statistical significance and correlations.

All these elements, fat oxidation, carbohydrates and lactate. They're very well connected. If we look in the other graph, this is the correlation between lactate and carbohydrates. We see that overall, the correlations are quite good, because lactate is the byproduct of glucose utilization. You may see that in the elite athletes, though the gap is wider here.

And this is for the same reason that we've seen earlier. They use a lot of glucose, they're. Using so much fat there as well, is really the point. So the bigger the gap between the blood lactate curve and the carbohydrate oxidation curve, the more efficient the individual is, the more they're able to oxidize fatty acid. Then they have to require glucose and clear lactate.

Yes, the mandatory byproduct of glucose oxidation is lactate. So here, the lactate doesn't show up in the blood, it stays in the muscle. It's hard to disentangle those two because you mentioned a good point that I omitted. This in part reflects the lactate shuttle. This in part reflects the ability for them to reuse lactate as a fuel, as opposed to just letting it get out there with hydrogen and start to poison sarcomeres.

Peter Attia
Let me see the other slide that you wanted to show that explains, I think, how the MCT transporters work. This is a little bit more of that bioenergetics of the cells of the main two substrates, which are fatty acids and pyruvate, and also lactate. Certainly, glucose goes through glycolysis and it ends up, this is the cytosol. This is the outside of the mitochondria, the inside of the cell and glucose. When it enters the cell, it's oxidized to pyruvate.

Inigo San-Milan
That pyruvate needs to enter the mitochondria through what's called the mitochondria pyruvate carrier, and it's oxidized to acetyl CoA, which enters the Krebs cycle. This is a complete oxidation of glucose through oxidative phosphorylation in the Krebs cycle and electron transport chain. Then fatty acids have the same mechanisms too. They also get converted to acetyl CoA through different mechanisms. Fatty acids are transported through CPT one and then cpt two go through beta oxidation, acetyl CoA, and enter the cell.

But every time that you use glucose, you produce pyruvate, and every single time, that pyruvate is going to be reduced to lactate always. And this is the key concept. So when you have a constant glycolytic flux. In one of the steps of glycolysis, you're going to utilize NAD and it's going to be transformed to Nad H plus hydrogen. So if you use this mechanism a lot, you're going to deplete NAD.

The only way that rescues NAD is the reduction of pyruvate to lactate, which replenishes NAD. Going back for glycolysis, and this is absolutely necessary for the continuation of glycolysis. But this lactate enters the mitochondria through a specific transporter, MCt one, and has a specific enzyme, LDH, that oxidize lactate, lactupyruvate, and going back to the Krebs cycle. So again, this is an extra fuel, but for that, you need to have these transporters very well developed. Let me try to explain this to people who aren't able to see the graph because this is such an important point.

Peter Attia
So you're showing a picture of the mitochondria. We're looking at the outer mitochondrial membrane. We're talking about three transporters, three things that let substrates from the outside to the inside, where they will undergo the most efficient form of ATP production. So the first is we have the fatty acids. They enter directly, then they undergo an oxidation where they get truncated into little two carbon chains, and they enter the krebs cycle.

We get that one, and we know why. That one's very good. What I think is very interesting here is when you contrast the two different fates of glucose byproduct. So the traditional way that we think about this glucose being reduced to pyruvate, pyruvate directly entering the cell through its own carrier, and then being converted to acetyl CoA, which follows the same fate as the fatty acid. Now, when energy demand increases, and we just looked at graph after graph that demonstrate that no matter how fit you are, at some point you have to produce more lactate.

So you now don't have sufficient cellular oxygen to go down that first route. So you start making lactate, but if you have enough MCT one transporters on the outer mitochondrial membrane, you can now bring that lactate in the cell and actually do the reverse of what just happened, turn that lactate back into pyruvate. Pyruvate becomes acetyl CoA, and everybody wins the game again. The game being won, of course, because now you're making 32 units of ATP instead of just the two units you would make converting pyruvate to lactate. So it begs a very important question, which is earlier, when you spoke about what makes Pogacar so remarkable physiologically.

One of those things is he must have a boatload of MCT one transporters on his outer mitochondria membrane. And that must explain in part why his lactate levels are so much lower than everybody else's at a comparable work level. How much of that is genetic and how much of that is a result of his training? Exactly. So you're right.

Inigo San-Milan
He has a much higher level to oxidize lactate. So there's a genetic component, no doubt about it. There's also an epigenetic component of. And as we know nowadays, the genes are not your fate necessarily. From the genes.

To be able to be transcribed and form a protein with biological action, the probability is less than 20%. Kind of what the science is showing. Roughly. This is the whole from genetics to transcriptomics, proteomics and metabolomics. It's about 20% chances that one gene is going to be ultimately expressed.

Obviously, we still try to understand all this. So these elite athletes, probably they have a much higher possibilities. But there's a long journey. And this is where epigenetics occur. It's like what you eat, how you rest, how you train.

And I think that the training is also an important component of this. This is, for example, why we train very, very specifically this energy system. And we try to dial in as much as we can specifically to try to stimulate this bioenergetics system and increase the MCt one s the transporters for lactate. As well as all the components in the Krebs cycle, which is the mitochondrial respiration. And also to increase also the mitochondrial pyruvate carrier.

Cause we might discuss later, this is already dysregulated in people or downregulated in people who are sedentary. But the thing is, if you see this next slide, you see it, okay, this is what makes the difference in these athletes. So this is a fast twitch muscle fiber and they use glucose. So this is when you're like a high exercise intensities, climbing or running at a high intensity, or swimming or whatever the activity you do, you need glucose. Because glucose is, as you said, very well.

It yields less ATP, but it does it much faster than the diesel gasoline, which is the. The fat. But when you use glucose, you're always going to produce pyruvate. The higher the intensity, the more glucose you need. More pyruvate you will need and the more lactate that you will produce.

So that lactate has, as I said earlier, two routes, one route is like it's exported through the MCT force, which is the transport of lack outside the fast twitch muscle fibers, something that also is strainable, the capacity to export lactate through high intensity exercise. And then it travels to the adjacent slow twitch muscle fibers. We blow up this mitochondria in the slow twitch muscle fibers. This is what will happen. The entrance of that lactate goes through another transporter.

MCT one is the same family, but instead of four, it's called MCT one. I mentioned earlier that lactate is converted to pyruvetin, acetyl coa, and goes into the Krebs cycle. So in these well trained athletes, like Borazar, for example, they have an amazing ability to oxidize the lactate inside mitochondria. At some point, every single human gets to a point that they cannot sustain the effort anymore. But what makes the difference is obvious, is like, these guys can do 400 watts for a long time versus a mermator who can not even do two strokes at 400 watts.

So what happens is, like, when you have a lot of the right MCT one and mitochondrial function, this lactate is going to increase and accumulate. And it's not lactate per se, but the hydrogen ions associated to lactate elicit an acidosis of the microenvironment of the muscle, which is something that we know, and we have learned also from cancer, the famous cancer microenvironment, which is very acidic. And that's going to interfere with different functions in the muscle, with both the contractile force and the velocity of the muscle fibers. I'm not saying that this is the cause of fatigue, by no means, because there are multiple theories and we still try to understand it's essential fatigue as well. And everything probably is interrelated, or it must be interrelated.

But the bottom line is, like, when this lactate cannot be oxidized, it is exported to the blood. And this is why you see that people with metabolic syndrome, for example, or type two diabetes, who are characterized by having a very poor mitochondrial function, they cannot, during exercise, oxidize this lactate. In the moment, they start using glucose, which is very fast. Also, because they don't have the slow twitch muscle fibers, mitochondria, to use fat, they need to rely on glucose. That's that metabolic reprogramming or partitioning they have.

They produce lactate, but they cannot oxidize the lactate. That's why this lactate chooses, mandatorily, the route of being exported to the blood. And in the blood, then it goes to any tissue in the body. So this is what I meant earlier about what is two millimoles versus one millimole. Whereas Pogacar, for example, he oxidizes a lot of this lactate.

So by the time that pogaciar saturates this transporter and this mitochondrial capacity to oxidize lactate, it's a tremendous, tremendous amount of power output and a tremendous amount of glucose that he puts out. So this is why that one millimole, 1.5 mmol and a world class athlete necessarily represent the same metabolic status of a 1.5 or two millimoles in the blood of a normal person. This is a fantastic tutorial in muscle physiology. And again, this very important distinction between lactate production at the local level and lactate that we measure at the global level, that's the challenge we have when we are measuring lactate. We cannot impute lactate clearance and lactate production.

Peter Attia
We can only impute the sum of those. It's originally thought, right, that these athletes, they don't use as much glucose. Well, in fact, that Richard shows, and Brooks and his team showed it, and others, too, that that well trained athletes, in fact, they use more glucose because they have to. You cannot do 400 watts with that massive amount of carbohydrate oxidation. And this is what we also see in the indirect colorimetry that you see people, recreationals, or people with metabolic syndrome, they have like 4 grams/minute at max carbohydrate oxidation, whereas elite athletes, they can get to six and a half grams per minute.

Inigo San-Milan
It's massive amount of glucose and they produce a lot more lactate. But the key it doesn't show up in the blood is the rate of appearance in the blood, because it's oxidized in the muscle. So it doesn't show up in the blood, is the balance of lactate production and lactate oxidation without getting to the blood. And this is what it correlates a lot, also with fat oxidation as well, and the graphs that I was showing earlier. So one of the things I want to ask you about here that is a bit of a confounder when we do this type of analysis, is the carbohydrate content within the diet.

Peter Attia
So I'll share with you my data, but I've now seen this with multiple people, including one individual who's remarkably fit. God, it's how many years now? Ten years ago, I was on a ketogenic diet for three years. And the very end of that three year period was when I kind of got back into cycling. At my fittest, as an adult cyclist, I was back eating a lot of carbohydrates, but there was about a six to twelve month period when I was still in ketosis, I was kind of getting back into cycling shape, and I do have one vo two max test from that window of time, probably six months after getting back to cycling and still on ketosis.

I've gone back and looked at the data and they're very interesting. What I would observe is maximum fat oxidation was 1.3 grams/minute and that occurred almost immediately and it sustained until. So at the time, my FTP was about 4.1 watts per kilo. This would have been sustained until about 3.5 watts per kilo. So at 3.5 watts per kilo, I was still oxidizing about 1.2 grams/minute and then that sort of fell off and glucose became then the dominant fuel source at the completion of the test.

When I was done, when I failed, I was obviously not oxidizing any fat and glucose oxidation was just under 6 grams/minute about 6 grams/minute about 24 kcal per minute. So I've also seen this with another athlete who's been in ketosis for seven years, is a very fit cyclist. Actually, he just sent me his data and it's comparable. In fact, he's much fitter than I was. So his 20 minutes FTP test is about 412 watts for 20 minutes.

And surprisingly, he has decent glycolytic power. So that's the other thing is I never really had good power at the low end because I only cared about time. So it didn't matter how many watts I could hold for two minutes or three minutes, I only cared about 1 hour. But this guy could still hold 1200 watts for 15 seconds, even for three minutes. He's north of 500 watts, 600 watts.

And again, fat oxidation is, you know, one, 1.5 grams/minute so it becomes a bit confusing because it would be very difficult to define zone two by maximum oxidation. So ketosis is an extreme example. But given how much RQ respiratory quotient, the ratio of vco two to vo two depends on baseline carbohydrate intake, how do we make the adjustment so that we understand and we're not being misled, because if you just looked at my data, you would dramatically overestimate my mitochondrial efficiency? Is that a situation where you say, well, actually the lactate. And unfortunately, I don't have lactate data from that test, so I can't tell you what my lactate levels were doing, but it might not be a problem in the peloton because you're not going to be in ketosis if you're trying to win the Tour de France.

But we do see a great degree of carbohydrate and fat variation in the diet amongst people that we're trying to test. How do you make that correction? My humble opinion, what we see in these cases, because I see them all the time too, is that there's an artifact in the metabolic heart. The metabolic heart measures gas exchange, and then through the equations it says, okay, this person must be burning fat or burning carbohydrates. The equations are calibrated on high carb diets, presumably?

Inigo San-Milan
Yeah. So the thing is like, as you exercise, no matter what fuel you're using, you keep increasing oxygen consumption, but if you don't have much carbohydrates, you're not going to produce much CO2. So that's going to tweak or mislead my stoichiometric equation, because the algorithm is going to think that, oh, whoa, he's using a lot of oxygen and not producing enough CO2, so he's got to be burning a lot of fat. That's when you see fats in north of 1 gram/minute those are fat oxidation. I think they're an artifact.

I see this because three days later, when you change the diet of that person, three days later, that person's fat oxidation might be 0.35. There's no way that the mitochondria adjusts. First, it reflects a very high fat oxidation capacity in someone who we know very well, who is not an elite athlete whose mitochondrial function is not incredibly high. To be able to oxidize so much fat and in three days reduces, like by three or four times. I attribute this to an artifact of the gas exchange.

And this is where, looking at lactate, it should give you those parameters. Normally, what I see in these individuals is that you see maximum lactates of two, three millimoles, because simply they don't have carbohydrates. Also, the thing when you see that, yeah, my maximum grams per minute of carbohydrates were in the six, but you're in ketosis, so how can you have enough glycogen or glycolytic capacity to elicit. Such a high carbohydrate production even when you're in ketosis? Remember, my blood glucose is still four to five millimole.

Peter Attia
I would really like to see this studied, because, again, even if you're only eating 50 grams of glucose, a day. Think of how much glycogen you're making from all the glycerol, from all the fat that's being converted to ketones. So, I mean, I think Jeff Volek and Steve Finney have looked at this, and when they put people into very, very strict ketosis, but do muscle biopsies, they're still seeing 60% of the glycogen content in the muscle that was there under high carb conditions. I mean, I think my capacity to oxidize five and a half to 6 grams of glucose per minute was still there. Just took a long time to get there, I think, is the difference.

So I guess the question is, if the vco two estimation is off because of the stoichiometric coefficients, do you think the vo two estimation is off also? No, I don't think so, because, as you said, very well, ketones are used for energy purposes. And then we have a third element which is absolutely key in bioenergetics, which is glutamine. Glutaminolysis, highly expressed and utilized. We have learned that from ICU patients.

Inigo San-Milan
ICU patients is a great model to study metabolism or stress metabolism. ICU patients, they utilize for wound healing about three times more glucose at rest than what we have. And it's part of the healing process. Glucose is instrumental for cell proliferation, wound healing, and part of this. Lactate too, as a byproduct, as a molecule.

But we see that, and this is a study that we published looking indirectly, a methodology to look at glycogen. It's a pilot study we did with ICU patients. They don't have glycogen. When you say they don't have glycogen, you mean liver glycogen, muscle glycogen, or depleted by how much? Depleted to what level?

Let's say that you have 500 grams of glycogen if you have a full, high carbohydrate diet. So that might not be the case of someone entering the ICU first, because they might not be elite athletes, or they might have maybe 300 grams, or they might not have that adaptation to hold more glycogen. So let's say they have 300 grams or so. By the time they get into that condition, the body uses about three times the glucose at rest. Now, an athlete used that same glucose, but a higher intensity, but only for a reduced amount of time, 2 hours, 3 hours, 4 hours, whereas the ICU patient is 24/7 so eventually the body is going to run out of glycogen in the muscle, or is going to be under huge stress.

The body has evolutionary mechanisms because it's a wonderful machine and it needs to continue. So it increases another route, which is glutaminolysis. So glutamine is an excellent source of fuel. It enters directly the mitochondria. We have seen in a publication that we're going to show when we publish it, is that when we inject mitochondria with glutamate, it's incredibly well oxidized.

Peter Attia
And what's the source of glutamate in these ICU patients? Are they breaking down muscle? This is where cachexia comes into place. We know that pretty much every single ICU patient becomes cachectic or suffers from muscle waste. And this is the syndrome, both sidesu muscle waste syndrome.

Inigo San-Milan
Why do they get cachactic or catabolic, and why they overexpress tremendously levels of glutamine? Because they need it for either enter the krebs cycle for energy, or for gluconeogenesis. So this is one of the things that we learned a lot from ICU. These ICU patients, they have hyperglycemia, yet they're not giving them, usually because they have hyperglycemia. It's true, too, that in the acute ICU phase, they also have insulin resistance.

But obviously, this hyperglycemia, and ICU doctors historically have seen this. It's like, whoa, this patient has hyperglycemia of the chart. So obviously, we're not going to give them iv's of glucose, we're going to give more protein and glucose, I mean, fatty acids. And in fact, glutamine has shown that increased survival rate in these patients. Where is this hyperglycemia coming from when you do not have glycogen?

It comes probably from proteolysis, where you break down protein from your muscles to release glutamine. We would only know that if we understood hepatic glucose stores, because regardless of how much glycogen is in the muscle, it's never going to make its way into circulation because the muscle can't fully dephosphorylate it. Do we have a sense of what the hepatic glycogen content is? Because I can't imagine the body would ever let anything compromise that, given that if the liver can't produce glucose continuously, the brain dies. So it might be that this is true, true and unrelated.

Peter Attia
Right. It could be that the muscles are depleting glycogen because of high utilization. But the liver, through gluconeogenesis, has plenty of glucose that's what's making it into the circulation because of hypercortisolemia, because of other acute phase reactants. And so we have hyperglycemia, but it's all being mediated by the liver, which has no trouble maintaining glycogen levels. And again, from an evolutionary perspective, you much rather err on the side of hyperglycemia than hypoglycemia under a period of stress.

Inigo San-Milan
Absolutely, necessarily. And that's, I think, what's the source of that gluconeogenesis? It's probably glutaminolysis coming from the muscle. So this is what my hypothesis, right, that those muscles, they eat themselves to feed themselves or to feed the rest of the body. So it would suggest that exercising ICU patients would be important, getting some load bearing resistance, even, of course, they're in a bed, but moving their extremities against a load supplementing with amino acids, could actually improve outcomes.

Absolutely. There's a lot of research in this area. My colleague Paul Wismeyer, who used to work here with me at the university, now he's in Duke, he's doing a lot of research and practical work with that, with this. It's like, yeah, this hyperglycemia probably comes from gluconeogenesis going back to where we started. Yeah, could be that there's a lot of glutamine released, you know, when you're also ketoacidosis state as well, especially in the first phases of that.

We know cortisol is very high at first. The same thing that we see in ICU patients, that two main parameters that are predictors of mortality at the ICU is a hypercorticular anemia, high cortisol levels and high lactate levels. They both are completely related. Anyways, I think this is fascinating. There's a great model to understand metabolism, stress metabolism of these patients and ICU patients.

And that's the other thing, too, once you exercise, and this is a very important concept for people with type two diabetes, with type one diabetes and hyperinsulinemia, is that you have insulin resistance and you have difficulty to translocate, therefore, to translocate the glut, four transporters to the surface of the muscle, the sarcolemma. And we know that probably the first tissue or organ where diabetes debuts starts is the skeletal muscle, because about 80% of the carbohydrates that we have, they're oxidized in skeletal muscle, and because we're at rest, should be oxidized within the mitochondria of skeletal muscle. That pyruvate this is what we research and seeing it clearly. But when you have insulin resistance, you cannot translocate those transporters. Now we have a second way to translocate those transporters that not many people know about, and that's muscle contraction.

Peter Attia
This is the insulin independent glucose uptake, which also seems to be heavily dependent on fitness. The fittest athletes here require virtually no insulin to translocate glucose into the muscle through the insulin independent pathway. I think we may have even discussed this, I don't know, over dinner one night. But you look at the type one diabetics who are highly, highly active, require very little insulin. Exactly.

Inigo San-Milan
This explains hypoglycemia in these patients. Shortly after they start exercising, they might have something to eat and they inject themselves with insulin and there's nothing you can do once you have insulin on board. So that insulin is going to translocate those transporters and it's going to start bringing insulin inside. I mean, sorry, glucose. In the moment you start exercising, you do the same function through contraction of exercise of the muscles.

So you have two mechanisms acting at the same time, pulling more glucose inside the cells, leading to hypoglycemia. So this is what we learned a lot with persons with people with type one diabetes and exercise, and then we can prevent them. So, for example, do not inject yourself before exercising, because exercise alone is going to take care of that glucose. But we can take these concepts also with people with type two diabetes that they have insulin resistance or pre type two diabetes. It's like, why not exercising right after you eat that carbohydrate you have?

You have insulin resistance already, but when you exercise, you're not going to need that insulin, and yet you can translocate those transporters and you bring glucose levels down. And I'm sure that you see this all the time with your glucose sensors. Yes. I've gone periods of time when I've done incredibly frequent lactate testing. So lactate testing every 30 minutes for a day or something insane like that, which is incredibly expensive and incredibly painful in your fingers, but you learn how much, for example, a meal impacts lactate.

Peter Attia
So when I wake up in the morning, my resting lactate level varies. I've been tracking this over a period of probably 40 days. So 40 days of tracking. What range do you think my morning resting lactate level has been over a 40 day period in the morning, first thing in the morning, I would say. Neighborhood of 0.8 to 1.21.3.

Pretty good guess. So, 0.3 to about 1.1. But that's a pretty big variation and probably median level of about 0.8. Yeah. In the neighborhood of wine, which is normally in the feed individual.

Inigo San-Milan
Yes. So then what I can do is I can eat a very high carb breakfast and go and do a zone two ride, or don't eat anything at all, and go into a zone two ride. Very different lactate performance curve. So the high carb meal raises lactate. So it becomes a bit of an artifact in a way which now gets me to.

Peter Attia
We've talked about this at the level of the most precision possible, the way in which I would measure it in a patient, you would measure it in a world class athlete, where we have the ability to do indirect calorimetry and lactate testing. But now I want to talk about it in the way that we train people, normal people. So we've talked about this, call it difference between the lactate level that you measure in the blood, which is now heavily influenced by production and clearance. And then we've talked about the gold standard, which would probably be fat oxidation, but even that can be confounded. But let's take off the table the people who are consuming a high fat, low carbohydrate diet, because that confuses things a bit.

If I have a patient and I'm looking at their biometrics, and we do a zone two test based on looking at their fat oxidation during an escalated test of part of a Vo two max test, and it comes back that their maximum fat oxidation, which is 0.3 grams/minute occurs at a wattage of 1.5 watts per kilo. That's a pretty average person, and I say I want that number higher. Both the absolute number of fat oxidation, but where it occurs on the graph now, I want you in a year to be 2.5 watts per kilo, let's talk about two things. One, how they should train, and that means duration, intensity, frequency, etcetera. And secondly, what we should use as the readout to know we're in the right training zone, given that they won't be able to train daily or weekly or whatever frequency with indirect calorimetry.

And by the way, let's assume that some people will want to use the point of care lactate meters and some people will not. Let's start with what's our surrogate for training zone, starting with what we knew. So we learned that 1.5 watts per kilo was maximum fat oxidation, but we want to increase that to 2.5. So what metric do you use to train them. Normally what I do is like starting with the metabolic test, I translate that information into whether it's watts or speed or heart rate.

Inigo San-Milan
All of them. Normally they correlate quite well and you can individualize it. There are people that don't have a power meter. You can do heart rate, for example, or people that just obviously they run or they walk can do speed or heart rate as well. Very good surrogate.

So that's the first metric, the surrogate, then it's about, at least from my experience, the three main principles that I've learned over the years on how to apply this. So first is frequency. Before we go to the frequency and the duration, I do want to go back and ask you another question. We have some patients who don't want to use a lactate meter, either because it's cumbersome or somewhat intimidating. We also add another metric, which is relative perceived exertion.

Peter Attia
RPe, I'll tell you what my rule of thumb is, but I'd like you to sharpen it, refine it, throw it out, make it better, whatever I tell patients based on my experience. So I don't know how extrapolatable that is when I'm in zone two, as confirmed by lactate levels. So call it 1.7 to 1.9 millimole, which is what I target. I can carry out a conversation because I do most of mine on a wahoo kicker. I put my bike on a wahoo kicker.

I can spend the entire 45 minutes on a phone call, but it's not as comfortable as this discussion here. I'm a little more strained, but if I can't talk, if I feel like I can't talk, I'm too high in the intensity. Do you think that that's a reasonable surrogate for people to use across the spectrum of. Not particularly fit all the way up to Pogotchar 1000%. And I use a cmetrix also with people who you mentioned they don't want to do a hardware lactate meter or they don't have access.

Inigo San-Milan
I get hundreds of emails about where can I do this test or is there anything that I can do? And I agree 100% with everything that we know at the granular cellular level. By injecting fuels and substrates directly into the mitochondria, we cannot get more cellular level and scientific than that. The surrogate or the percific exertion, it works beautifully. I know that people are coming out with different algorithms based on Hari variability or DFA, one alpha, etcetera, but honestly, I agree 100% with you.

I always tell people, if you can exercise, whatever the exercise you do and maintain a conversation like you and I are doing, you're way too easy. You're probably zone one. If you can talk, but it's some form of strain, you can talk for 2 hours, but we're talking a little bit like that. You're just at that threshold. Put it this way.

Peter Attia
Litmus test, I tell people, is the person on the other end will know you are exercising. Exactly. You will not be able to mask from them that you are exercising. Exactly. And in fact, I have many conference calls with people that I know to be respectful, but I do it on the bike.

Inigo San-Milan
They call me, and I'm on the bike, either outside or in the trainer, and they tell you you're exercising right, because you can feel it. But yet I can maintain a full hour meeting on the bike without bothering the other person because they can understand me. But he said, if you cross to the point where you cannot maintain that conversation, you need to breathe much faster because you're producing more CO2. And that's probably because you're already transitioning from the slow twitch muscle fibers to the fast twitch muscle fibers. More glycolytic, more lactate, more CO2, more buffering capacity.

It seems old school, but it works beautifully. Agreed. And the other thing I do because I really like people to triangulate and give them a starting point. So if someone has not done a metabolic test yet, and that's usually the case, by the way, is that we're starting with just a zone two training protocol. I also give them some ranges on heart rate.

Peter Attia
Now, here I have found much more variability. So the first thing I say is to do this, you do need to know your maximum heart rate. Not your predicted maximum heart rate, but your actual achieved maximum heart rate. In my experience, personally, my zone two is actually at about 78% to 81% of my maximum heart rate, but I know that for less trained people, it's lower. So I tell people a broad range of 70% to 80% of your realized maximum heart rate is a good place to start and then make adjustments based on relative perceived exertion.

Inigo San-Milan
I agree. What do you know about heart rate? I would agree that I usually also say the same thing, somewhere between 70 to 80. That being said, right, if you want to be very. That's a big range.

It's a big range, exactly. So you can be at 70, let's say, at 1.7 millimoles, and then at 80, you can be at five millimoles, you're completely away from one zone. But as you said, it's a good starting point. And as you very well said, and I agree 100% with you, is like, yeah, then you tweak it with your perceived exertion. The other thing too, with the heart rate, and this is where the heart rate variability, there are different interpretations.

So the modern interpretation, the heart rate variability is the differences between bit to beat. And that's where there are different algorithms. For me, the heart rate variability, it's more at a broader spectrum, and it's more on the adrenergic activation that you have. So, for example, your fatigue today, first of all, normally you're going to wake up with your resting heart rate a little bit higher than normally. If you're a normal heart rate, let's say it's 50 and you're being fatigued, you might wake up with 65.

So that alone is a heart rate variability concept. It varies from the norm to one day. So that's our red flag. That you might be tired a day, might not be super sensitive, but it is very sensitive for elite athletes, without a doubt. Of the second aspect is like when you go out there and exercise, as you might see, there are days that you are like 130 beats per minute, whatever you think your zone two is, 100 3138, for example.

But some days, it's really hard to get that heart rate. You're already struggling at 110 bits per minute or 115 bits per minute, where that's not the norm. That's another deviation. That's a variability of the heart. So this is what I've been historically used for, heart rate variability, which tells me a lot more information.

This is what all the athletes also tell you, like, man, my heart rate doesn't get up today. You see, on training peaks, you see when someone is fatigued, they do an interval and they know they always 100 8185, let's say they lactate threshold. And today they cannot get up until more than 170. You see, in the competition the first week of the Tour de France, their maximal heart rate, let's say it's 195 last week, the maximum heart rate is a 170. That's what I interpret by heart rate variability.

And I know that a lot of people might criticize me because all that has nothing to do. Well, no, I think it's macro versus micro. I agree. I read it as macro versus micro. I'll share with you an interesting self experiment I've done a couple of times.

Peter Attia
It's not pleasant, but it's interesting. If I take a huge dose of a beta blocker and the only beta blocker you can do this with. If you have low blood pressure, as I do, you have to be careful. But propranolol is fine because it really. It disproportionately lowers heart rate, but not blood pressure.

But I've done this experiment a few times to test an idea, which is would taking all of the gas out of my heart rate allow me to push harder and generate a higher zone too? And it turns out it does. So my zone two is just under three watts per kilo. I really want to talk with you about getting over three watts per kilo. I'm still furious because in July, remember, I was at 2.95, I was just kissing on the door of three.

I've come back, you know, I'm now at about 2.75 to 2.85. So I've lost a bit aging too. We're going to talk about training in a moment, so. And for me, I'm at that upper end of maximum heart rate. So I'm going to be doing that at about 80, 81% of maximum heart rate.

But if I took propranolol, 60 milligrams of a time release propranolol, I will be able to get over three watts per kilo and I'll do it at a heart rate of 68% of maximum. But it feels horrible. I feel like I'm going to die. It is the worst feeling in the world. And it's not pain.

I don't know how to explain it, other than it feels like what it feels like when you're overtrained. It feels like you just can't get moving. It's like an engine that's being taken from 9000 revolutions per minute to 6000 revolutions per minute, but yet somehow is able to generate the horsepower. But it just doesn't feel right. So that's my drug cheating way to get over three watts per kilo.

But more to illustrate the point, right, which is when you put the governor on, on heart rate, you can get there at a lower heart rate. Subjectively, it's a miserable feeling. Yeah. And this is kind of, in a way, what happens when you're fatigued, when you don't have enough fuel. Again, going back to, like, my heart doesn't get up today and I'm struggling.

Inigo San-Milan
If you were taking some beta blocker. But the thing is that it has to do a lot with fuel, for example. And I experiment this a lot too. I try to understand how this works. So I do.

Maybe intermittent fasting for a few days, and I go out there and good at adjusting at that, and I cannot do that. I know others can do it, and I admire that, but I can see my heart rate right away. When you don't have enough glycogen storages, it's very possible that adrenergic activity is decreased. You need to break down glycogen, and we know that what takes to break down glycogen is phosphorylase in the muscle, and that's directly regulated by catecholamines. So when there's a decrease in glycogen, this is my hypothesis, when there's a decrease in glycogen storages, because of the evolutionary mechanisms that humans have, the brain is the boss.

The brain says, like, I don't care about your legs, but don't use up all the glycogen, because you have to give me, and the liver has to give me glycogen as well. So I'm not going to shut you down completely of breaking down glycogen, but I'm going to slow you down. So I'm going to release less catecholamine so that you break down less glycogen. The collateral effect of that is the heart, because the heart contractility is regulated by catecholamines as well. So this is why using that, my version of heart rate variability, it's quite useful.

I've been using it incredibly successfully for 25 years with my athletes, where I see that, hey, your heart rate is not going up today. Usually it's 185, 190. For example, when you do a lactic threshold, for example, in today it was 170. So tomorrow, take it easy or pile up on glycogen. I mean, on carbohydrates, or take an easy day, and you see how you're going to be very responsive the next day, the following day.

And in fact, that's what happens. I would say ten out of ten times, but let's say nine out of ten times, right. But I do that with myself as well. And I see is also I work a lot with the head. You think a lot, and the brain uses about 100 to 125 grams of glucose daily when you go.

And I don't know that fact. When you work a lot of hours and thinking and thinking and thinking and stressed, the brain might need a lot more glucose. So that's draining your glycogen storage from the brain, probably, and even from the muscles, because the muscle can release glucose to be utilized as well. Yes. The muscle has phosphorylase and can be degraded to glycogen and that glucose can go to the circulation as well to feed other organs.

Peter Attia
I didn't realize that we had glucose one phosphatase in the muscle. I thought the muscle glycogen's fate was sealed in the muscle. It's possible. There are a few studies. I'm happy to send them to you.

Inigo San-Milan
I cannot refer them out of memory, but the muscles can also release glucose and export glucose. I assume this is a relatively small amount compared to what the liver is doing. Yeah, absolutely. Exactly. But it's possible too.

Those days where I'm thinking a lot and I'm very stressed and I'm not dieting or anything, I just go out there and I'm dead. And I'm sure that many people listening to this feel the same way, like, what the hell is going on today? I don't have energy at all today. And you will see that your heart rate doesn't get up those days. And you can get to that by just training 5 hours a week or 7 hours a week.

And sometimes people say like, look, I cannot be overtrained because I only train 5 hours a week. Yeah, but you're overworked. That's a big artifact with your training. That's what most of us are aspired to, pre retire before 60 so we can have more time to exercise and less time to work. But yeah, that's what I do this, I take a day off completely, I sleep more, I increase my carbohydrate intake, and the following day I can even break my pr on a climb or something.

I feel like a million dollars. So resting recovery is key for that. I think this is a very important point and it's actually something I've only been able to pay attention to in the last year, which is I used to judge my performance by training load. I used to use training peaks when I was training. I don't anymore.

Peter Attia
But the concepts of acute and chronic training balance any day that was suboptimal could be explained by training volume in some capacity. But now my training volume is relatively low. It's 10 hours a week of total training. That's both cardio and strength. This is not a lot of training.

And yet when I'm under stress, work wise, I'm just doing too much. I don't even use the word stress. It has a real negative connotation to it. I just mean when I'm overworked, when I'm doing too much, my performance, I have to either adjust my parameters for what I deem successful, or I just have to cut back on the actual training a little bit of to make time for more sleep or more relaxation. So I think that's a very important point that is easily lost.

So we've got a very good handle on the metrics we're going to be using. So now let's talk about two scenarios. The first is the person who is new to this type of training, so they've listened to this podcast or they're one of my patients and I've made the case convincingly to them that you really need to do this type of training. I want to come back, by the way, to a justification for that. So let's explain why high intensity training is not sufficient, but we'll park that for a moment.

But they really don't have much of a background in this type of training. Maybe they do some high intensity training, they do some weights, they play some tennis, but they really don't do the sort of steady state sustained cardio that we're talking about. How would you structure a training program in dose, duration, frequency for that individual and tell me a little bit about the choices that you would make if they're agnostic to running, walking, cycling, rowing, swimming. I have my biases there, but I want to kind of hear what you have to say about it. I want to apologize to many of your audience because I get a lot of emails asking me about these questions and it's hard to keep up.

Well, that's why we're doing the podcast, so you don't have to apologize. It's easier to do it this way. I appreciate it this way, but still I get emails. And before I used to see people here at the university, but now at the university don't have these services trying to convince them that the services are important to offer to population. But anyways, I want to apologize because I cannot answer to everybody.

Inigo San-Milan
I have the three main rules or parameters that I have learned over the years. So one is the duration. We have in mind sometimes that this is like endurance training, long days, like I only have 6 hours a week or 7 hours a week at most to do this type of training or less. There's no way I can do that. It's usually less because they might have 6 hours a week for total exercise and we're going to take half of that for strength training.

Exactly, which is very important. As you know, it's where I fail because I should do more of that. And I try to get a little bit more of time to do that. It's not easy, but I aspire really to dial that in. But yeah, you're right, they might have less than 6 hours and they might think like, well, I'm not an endurance athlete, so you need to do 4 hours to accomplish this.

So therefore I'm just going to move to do just high intensity and just get out of the way. That's not completely true. You can accomplish very important mitochondrial adaptations and very important metabolic adaptations by exercising 1 hour. Let's start by the duration. If you try to do that 1 hour to 1 hour and a half range, you're on target.

Peter Attia
Is that total or one setting? Meaning is it one to one and a half hours per week or does that need to be in one continuous exercise bout? So the frequency that I see is that this type of training ideally needs to be done between three to four days a week, ideally. And how can I know this? I know this because I've seen in the laboratory everything.

Inigo San-Milan
The person who trains one day at this zones, or two days or three days or four days, or high intensity, low intensity. And I see the adaptations. How do I see the adaptations? Again, looking at fat oxidation, lactic cleanse capacity, all surrogates of mitochondrial function, I've been identifying the dose of that training. So if you train once a week, there chances are that you're going to deteriorate over time and especially as we age.

Something that I see, for example, in high intensity exercisers and bodybuilders, they have a very poor mitochondrial function compared to people who do more. A little bit of everything. So one day a week is not going to work. Two days a week it might maintain what you have, but if you are new to an exercise program, might not be enough. Three days a week.

Now we're starting to see for sure four days a week. Now we're talking ideally five days a week or six, but not everybody has obviously six days a week to train. I think that you are a very busy guy. I'm very busy guy. Try to squeeze four or five days a week, maybe six in the summer.

But four to five days, it's achievable for most individuals and put aside an hour to an hour and a half. So I would say that four days a week is ideal. That's the first principle. The second principle is the duration. Going back to what I was saying with 1 hour, maybe pulazar needs 4 hours, 5 hours to keep increasing those huge mitochondria for a long time.

But a mere mortal, especially someone who might be pre diabetic or might be out of fitness or hasn't exercised in a long time, or someone who coming from a disease or a mother who just had a baby and has been out of shape for a while. 1 hour. If you walk or if you run might be very, very good for you. 1 hour walk or run, you might have to bring it up part of the plan, too. You cannot start off the bat with 1 hour.

You might start by 20 minutes, 30 minutes, 40 minutes, increasing it, maybe about an hour. And if you bike, for example, about an hour, 20 minutes, hour and a half. That's what I see, that if you do that for four days a week, things are starting to move. Even if you bike on a trainer, where you can be much more efficient and you can really get straight to the wattage and stay there. We tell patients again, it depends where they are in their cycle, but if they're starting out, I mean, we'd be happy if they give us 30 minutes, three to four times a week of dedicated exercise.

Peter Attia
I can't do zone two on the road. I can really only do it on the trainer. I just can't stay at a constant level on the road with starting and stopping and wind and hills and stuff like that. That's a very good point. That's why an hour and a half on the bike, it might actually be 1 hour or so because you have all these artifacts.

Inigo San-Milan
But you're right, when you're on the trainer, you isolate everything completely. And what I also recommend is about an hour, if you can get there. But again, you know, like, yeah, sure, you might. To me it's. It feels like a torture sometimes to be an hour on the trainer.

I hate it. I like to be outside, but we have how to do it. I do it. I watch a movie or just catch up on work. I have one of those special desks where I can type or read articles or answers and emails.

Low key activity, because again, you're not very sharp to think very intellectually. But yeah, 1 hour might do the trick. What I've seen is like, yeah, in those people who haven't done much at all, even 30 minutes, 20 minutes, might start moving the needle, but eventually it's not enough dose. The body needs more. If you can get to a goal, about an hour to an hour and a half, that should really work, in my modest opinion, in my experience.

So that's the duration. And the third is always the frequency, which we have talked about, which is usually the zone two. That being said, I think that it's also important to stimulate other energy systems like the glycolytic system. And again, continue with the model that we do with elite athletes. People think that elite athletes, whatever the sport are, all they do is high intensity all the time, and intervals, intervals.

And it's the exact opposite. If you look at the workload of an elite athlete, whether that elite athlete is, especially in individual sports, it's easier to see this. Whether it's a triathlete or a cyclist or a marathon runner or a swimmer, 100 meters swimmer is under a minute, maximal exercise. If you look at the workload, it's very similar. The majority of the sessions are in the lower intensity.

They're not intervals, intervals, intervals. And I always say, we cannot be so naive to think that the best coaches and athletes in the world haven't figured this out when they're always trying new things and they want to try the cut and edge things. Obviously they have said, oh, our sport is swimming under a minute. All we need to do is like intervals, intervals, intervals, intervals. Well, if you look at what swimmers do, they train.

And if you ask Michael Phelps, hours and hours and hours and hours and hours. Because if you can travel through the competition in that under a minute with a slightly better function to clear lactate, even if it's one millimole or less, the muscle contraction force might be improved. So all the hours and hours and hours might be that, just to improve a fraction of a second. But anyway, so this is what I'm seeing, that these concepts of glycolytic capacity and high intensity training, they're necessary, but they're not what the elite athletes do. The elite athletes have the best metabolic function of any humans.

Why not try to imitate their philosophy of exercise? And so, just to come back to the frequency duration question, I think the answer to the following question is going to be the more frequent training sessions. But if you compared four training regimens that were 4 hours a week, each one of them would be 460 minutes sessions, one of them would be 380 minutes sessions, one of them would be two two hour sessions, and then one of them would be one four hour session. So it's the same total volume. And notwithstanding the brain damage of one four hour session, is it safe to say that the 460 minutes sessions, because it's a higher frequency, would be the optimal one there?

I would say so. I think from my experience that it might be better, is the frequency. It's like if you take a medication, if you take a medication twice the dose and only three days a week, might not work as well as if you take the right dose every day. Because at the end of day, we're talking about the whole exercise as medicine, right? How do we prescribe that?

What's the dose? What's the frequency? I'm assuming that you will have to take it as many days as possible. I would say that it's better to do that. That being said, obviously, if you have the weekend and you have the possibility, which I don't have to do 3 hours, go ahead.

And another thing I wanted to point out is that for many people, they need that adrenaline for training. So other people don't care. Other people say, whoa, I love this. I don't like to kill myself into high intensity. But I think you need to do some high intensity at some point.

Peter Attia
I want to talk about that. So how do we bring in the other energy systems of the four pillars of exercise in my world? Stability, strength, low end aerobic, which I describe really as. Talk about it as kind of mitochondrial efficiency. And then high end aerobic, which is peak aerobic capacity, anaerobic performance.

So anaerobic power, peak aerobic, low end, aerobic. Mitochondrial efficiency, strengthen stability. Of those four, I, for some reason struggle to make the time for the peak aerobic, in part because, one, it's the least enjoyable. If we're going to be brutally honest, if you're doing it right, it hurts the most. It's also no longer as relevant because I don't compete at anything.

I actually really enjoyed that type of training when I competed. Because you have to spend time in that energy system. And you see the rewards of 60 minutes of repeating two minute intervals or something like that. So if we're really talking about this from the lens of health maximizing health, the data are unambiguous that vo two max is highly correlated with longevity. There are not many variables that are more strongly correlated, but the levels don't have to be that high.

Pogotcher's Vo two max is probably 85. It's probably in the eighties, at least in terms of milliliters per minute per kilogram. But someone my age to be considered absolutely elite, which means the top 2.5 to 2.7% of the population, which carries with it a five fold reduction in risk to the bottom 25% of the population. My Vo two max requirement is about 52 53. So the question is, can I use that as the gauge for how much high intensity training I need to do?

Basically just enough to make sure I maintain that vo two max? Or do you think about it in a different way. Well, I think about it more by energetics, energy systems ultimately. And we know that longevity is also high related with mitochondrial function and metabolic health. I think that more and more, this is what you see in so many fields in medicine nowadays, everybody's stumbling upon mitochondria.

Inigo San-Milan
So there's an aging process where we lose mitochondrial function, and there's like a sedentary component where we lose mitochondrial function. I wish that we could have a medication or pill. You could take it and increase the mitochondrial function because it would increase metabolic health and longevity. But the only medication that we know is exercise. Within exercise, the dose that we see that improves the most and also is sustainable in the long term, which is another important concept.

Very high intensity training is not sustainable. Very extreme diets are not sustainable. If you combine both, it's even worse. And this is what a lot of people are doing together. But you need to have some sustainability.

But this is important to improve that mitochondrial function. But going back to high intensity, I think, is necessary because we also lose glycolytic capacity as we age, and it's important to stimulate it, as you very well said. For all of us who are not competing, I couldn't care less about being super high intensity. I'm not competing. But that said, I want to have also my adrenaline rush, but how much.

Peter Attia
Does it feed into it? So, for example, if, and I've often thought about this now as I just want to make sure my zone two is above three watts per kilo, would I be better off taking that extra training? If I have one additional training session per week, should I make it an additional zone two workout? I do four. Now, should I be doing a fifth one, or should I be taking that fifth one and doing a vo two max protocol?

And that's what we'll typically prescribe to our patients, is a four by four protocol of highest intensity sustained for four minutes, followed by four minutes of recovery, and then repeat that four, five, six times. When you put a warm up and cool down on either end of that, that's a little over an hour. Would you spend that hour doing that in an effort to make your zone two even better, or would you just do an extra hour of zone two? I agree that if you have a fifth day, you can convert it into any type of high intensity session structured. What I can tell people, hey, you're a cyclist or a runner and you want to go with your friends.

That's your group ride. The group ride, go ahead and boom, go at it. Or if you don't have that possibility. This is my situation, for example, where I don't have the time to train more than an hour and a half, usually 2 hours max. So what I do almost on every session, I do my zone two, so it's clean.

Inigo San-Milan
And at the end, that's when I do a very high intensity interval. Tell me the duration. So if you did an hour of zone two. Yeah, so I do usually, let's say an hour and a half. So you'll do an hour and a half of zone two three or four times a week?

I shoot for four or five. Not all the time is easy, but, yeah, I shoot four or five. And I try to be strict on that, but. And unfortunately, that where I live, I live more in a Thailand area. So you have to go up.

So the last part, I just go at it. Sometimes you find another cyclist and you just compete, you know, to see who's the fastest in that short climb. But I try to do like a good five minute interval, roughly. I arrive home like, man, I kicked my ass today. This kicked my ass today.

Or sometimes you try it and you don't have the energy, as I mentioned earlier. Oh, my gosh, I can barely move the pedals today. I just quit and go home. But when I feel fresh, I stimulate that glycolytic system. What we know well, too, is that increases the mitochondrial function.

It takes months or years. Increasing the glycolytic system, it takes much, much less amount of time. You can do that in weeks or months if you stimulate on a regular basis two days a week or three days a week. At the end of that zone two, that's where you can target both energy systems, the oxidative mitochondrial system and the glycolytic energy system. We don't blunt the benefit we had from the zone two.

Peter Attia
If we immediately follow it with the zone five. No, because that's done. What I see is if you do things in the middle, but you don't. Want to do the reverse order, you don't want to start with the high intensity. Exactly.

Inigo San-Milan
One of the things, because you start having all these hormonal response. And also, you see you have high lactate levels in the blood. And what we know very well is that lactate inhibits lipolysis. So if you have a high interval in the middle or the beginning and you don't clear lactate very well, you might have high lactate levels for a while, and it's going to inhibit lipolysis. Also, another study we have under review, lactate at the autocrine level decreases the activity of CPT one and CPT two, so it interferes with the transport of fatty acids as well.

That's where, if you do all these, you might change things. You have high cortisol. Cortisol anemia as well. I'm glad you raised that, because I explained this to patients when they say, I went out and did a two hour ride today, and it showed me that I spent 45 of those minutes. 45 of those 120 minutes were in zone two.

Peter Attia
So I did 45 minutes of zone two, and I said, no, you didn't really do it, because you were going up and down and up and down and up and down. And so that's not the same as spending 45 minutes in the dedicated energy system. Right. I mean, when I look at the training peaks, you see the elite athletes. They're like, more power output and heart rate.

Inigo San-Milan
This is, like. Goes together incredible. Whereas, yeah, you're right up and down. The average might be zone two, but actually, you're between oscillating zone one, zone three, zone four all the time. So if you don't mind sharing in watts per kilo, what is your zone two in Colorado, where you're at altitude?

I don't look so much into this. I have done so many tests in my life since I was 15 years old. I was using a heart rate monitor, talking about 1986, when the first heart rate monitors came out. What you're getting at is you don't like to have a lot of data when you're doing it. You're going off RPE, and you're not looking at your power meter or a heart rate monitor, and you're not poking your finger when you're done.

I do it here and there because I still want to look at this, and I do metabolic testing here and there. But I've done so much on me since I was 15 years old, and I was obsessed by this. I got to a point that I know my body quite well. I can just go by the sensations. But here and there, I double check.

Peter Attia
But it's hard for you to then get at what I've observed. The few times I've tried to do my zone to at altitude, like in Colorado, it's an enormous discount. I feel like it's a 20% discount at altitude. Yeah, mine's around 2.52.8, something like that. Watts per kilogram.

Inigo San-Milan
When I do it at sea level. You'D be over three, probably, based on what I experienced, it going in the reverse direction. Yeah, I would say roughly. And one thing that I'm very proud of is that I have been doing, because I do sporadically, this testing, and I know my prs, because that's another thing, we have climbs here, and one day I go for this climb, and I go full out on that climb. Right?

I'm 50 now. I have the same metabolic parameters that when I was 40, to me, I'm very proud of this. And when you say parameters, you don't mean times up the climbs. Which parameters are the same? Lactating power output.

Vo two. I look at time as well, the pr that I had, it was similar. What's your Vo two max now? So my Vo two max now is four liters per minute. So that's about 51, 52.

Peter Attia
You could easily raise that if you lost three kilos, which you could probably do. Yeah, yeah, yeah. And the thing is, because I've obviously, when I was a cyclist, I was 141, 143 pounds. So my v two was. And you were probably.

Your Vo two was five and a half liters or something. It was 76.7. Let me see. It was 4.5, I believe it was about 4.8, something like that. 30 years later, I have decreased only about 0.50.7, which.

Inigo San-Milan
Whoa. I'm really happy about that, because I'm not training like I did, but this is one of the parameters. But in a decade, I haven't decreased my parameters. So this is, to me, it's a proving point to myself at least, that doing this routine, it helps to maintain that metabolic health that you had a decade ago. Now, can you do this ten more years?

And when I turn 60, I don't know. But what I know is that from others, I'm seeing it. So I see, typical person who just retired, as I discussed early, aspire to pre retire at the age of 60, or a little bit before. And these are like people like us, we are struggling to squeeze in time. Do 5 hours here, 6 hours a week here, or tend to, but then they have the whole time in the world sleeping.

They're not overworked, they can exercise. It's unbelievable and super inspiring how much they improve in their sixties. I've seen people in their seventies with the metabolic parameters of people active, morally active, in their thirties, world champion in the cycling, who's a 81, in the category of 80 to 85. Believe me, there's a category of that metabolic parameters were those of someone in their thirties, healthy, active. So this is incredibly inspiring.

Then I think that we're rewriting what's been taught to us in the books. Was that person an elite athlete. Were they a professional athlete in their twenties and thirties? Never. And this is what struck me.

He was a smoker, hypertensive, and he started cycling because he needed to change his lifestyle in his forties, because that's the same question, like, whoa, you must be doing this all your life. Like, no, I started riding my bike when I was in my forties. I was a smoker. I was heavy, I was hypertensive. Like, what?

So it's incredible 40 years later, what. I take away from that as well is the benefits and the importance of compounding. You see, you alluded to it earlier, and I think the listener could be forgiven if they missed this point. You can make relatively quick changes in your glycolytic efficiency. You can take an untrained person with a vo two max of 20 mil per kilogram per minute, and you could take them from 20 to 30 in a period of months.

Peter Attia
With the right amount of training, a 50% improvement in a few months. It's very difficult to see a 50% improvement in mitochondrial function in a few months. You've already made this point. But I just want to restate it because it's important to set expectations, and it speaks to why this level of training should be thought of in the same way that you think of accumulating wealth. It's day in and day out, day in and day out.

Small compounded gains over years and years and years is why a 40 year old overweight smoker can become a world champion at 80, because he probably never once again got out of shape in that 40 years. Absolutely. And this is incredibly inspiring. When I see these people in their sixties, just retired, and they come to do their first test, and one year later they come back. It gives me the goosebumps, because it is like, oh, my gosh, I'm 64.

Inigo San-Milan
I feel strong as when I was in my thirties. And, like. And of course, no medications. Really good state of mind, which is absolutely key for longevity. They eat in moderation, but they can have a little bit of everything, which is also, in my modest opinion, is part of the enjoyment of life, eating what you like in moderation as well.

So it's incredibly inspiring in a way. We're rewriting what we've been being thought for years, that once you turn 40, everything is going down. You can really, really change. And again, you own your own body, and you can really take ownership of that and improve it at any age. You mentioned drugs.

Peter Attia
I want to talk about one drug in particular, and maybe some supplements. You and I have spoken so much about this. And myself and another person are committed to funding a study that we're going to be doing once we get through kind of the backlog of COVID issues at the university. The question really arises around the use of metformin. Metformin and whether or not there's a true impairment of mitochondrial function, or whether the elevated lactate levels we see in patients taking metformin is an artifact of the drug itself, but says nothing of the mitochondrial function.

Do you have any more insight into this question that we struggle with greatly because we have some patients who take metformin who receive much benefit from taking metformin, but it makes it confusing to interpret their zone two data. And it makes me ask the question in those patients, it's maybe less relevant, but now it becomes relevant when we think about using metformin as a giro protective agent, an agent to enhance longevity. We need a lot research on that, I think, to understand this better. Definitely. It seems to work in many patients.

Inigo San-Milan
Obviously, for those ones in the pre diabetic first stage diabetes, it's a very good medication that's been used for a long time with good results. But how about the long term results? We know that metformin inhibits complex one, which is key for mitochondrial function in the electron transport chain. We don't know the long term effects of metformin in longevity. This is where I think that we need more information as well.

We see someone showing up with lactate of 3.5 millimoles at rest. And the first thing I ask is like, are you going to metformin? And many times, yes. And I'm sure you see the same thing. Right.

Wow. It's definitely an artifact. And why do you see at rest 3.5 millimoles or three millimoles of lactate? They're fat oxidation, commensurately suppressed, because when you metabolically test them on the cart, do you see in that individual a very, very low fat oxidation? If not, it might suggest that that lactate level of two or three millimole is an artifact, but doesn't really speak to what's happening in the mitochondria.

Peter Attia
Right. I haven't seen people taking metformin as medication, you know, for longevity, for example, or for health. What I see, people on metformin are. Already clinical patients, so of course they're low. Yeah.

Inigo San-Milan
So they're taking metformin in the first place because of their clinical condition, which is driven by a mitochondrial impairment or dysfunction is difficult to discern. But, I mean, I'm sure, you have more experience of people taking metformin. We do. But that's why this study that we're eventually going to get around to doing is going to be so important, because it will answer this question directly. We can do the muscle biopsies, and as you say, does it really mess up with the whole mitochondrial function or even like the mitochondrial function overall, override that inhibition of complex one and override other pathways?

I don't think we know the answer to that. Do you have an insight into any other supplements? No shortage of supplements that are out there that are touted as longevity boosting agents and mitochondrial health agents. So the most talked about of all of these, I think, is the precursors to NAD. The most common of these would be NR or NMN, both of which are pretty clear that they are precursors to NAD.

Peter Attia
There's certainly some debate about how clinically relevant it is. Do you have a point of view on whether or not taking a supplement that boosts NAD, at least in the plasma? I still don't know how well it's boosting NAd in the cell. But do you have a sense of if that is beneficial to the mitochondria, both theoretically, but more importantly, experimentally? I don't think we have the answer, but I think we need to be cautious about how we interpret this data.

Inigo San-Milan
It's definitely been shown multiple times that NAD levels, the cellular level or an even mitochondrial level are decreased with aging. Therefore the whole thing. Well, if it's low, let's take it. But it's not only NAD. If you look at so many metabolites at the cellular level and mitochondrial level, they're down regulated with aging.

The question is why are they down regulated? Is because mitochondria, per set to start out with, is down regulated, so it doesn't need so much nAd because cannot take it or other supplements or other metabolites. This is at least how I think of NAD, as we mentioned earlier, is very important in glycolysis and redox status to maintain redox. And it's very important in the visceral three phosphate, two, two, three biphosphoglycerate phosphate, where NAD is utilized to convert glycerol three phosphate to two, three phosphoglycerate, but is depleted. And this is why the only thing that rescues that is lactate.

Right, as we mentioned now, taking nad, is that going to increase longevity? I don't think so. That's my opinion. Because longevity is not just one supplement or two or three or four or five it's a compendium on an incredible amount of things that happen at the cellular level. And I don't think that one supplement, I remember those days where resveratrol was the thing for longevity, and everybody was.

Not everybody, a lot of people were buying resveratrol. And there are studies with mice showing that increased 50% longevity in mice, or therefore, let's do it in humans. Well, as you probably know, a lot of people started to take in resveratrol when they were 50, and they're dead now. It doesn't increase longevity in humans. The data in the mice, we can debate the merits of that.

Peter Attia
I want to ask you about a theoretical risk, though you kind of alluded to it. Isn't there a scenario under which too much NAD could be harmful? I don't know if this study's been done, but if you took cancer patients or patients who had tumors that were undiagnosed and gave them, if you doubled their NAD levels, wouldn't you actually favor the tumor's metabolism? Well, in fact, we have done that pilot study with mice. The whole thing is like looking at, in my area of research in cancer, is cancer metabolism.

Inigo San-Milan
And we know that glycolysis is key for cancer, and NAD is absolutely indispensable to feed that glycolysis. The question is, like, as you said, would nad increase that glycolytic rate, or glycolytic flux, therefore, would be favoring more cancer phenotype. So what we did, we haven't published that. It's a pilot study. We just were curious about it.

And we had two mice. We have NNF, eight mice, four and four. So what we did is we transfected tumors, triple negative breast cancer. It's very aggressive, and it grows very, very fast. One group, we give them just water, and the other group, nicotine namida riboside, which is the NAD precursor, because NAD, obviously, as you know, you cannot take it, you need to take the precursor.

And we observe the tumor growth over 23 days. After that, the IRB at the university, because you cannot have animals with high tumors. So it was a flank tumor, and you need to harvest them. We were measuring every five days the tumor growth, and we saw in these animals that there was about 15% increase in tumor growth. In the NAD group, you saw that.

Peter Attia
Difference with only four mice in each group. It's four and four, but all consistent. We have statistical significance even with a small four. I mean, there was no cross results. All the four mice, they grew cancer at a higher rate in the NAD than the control group.

Inigo San-Milan
Again, that's where, like, obviously, this is not like a publishable. Is that a study you'll repeat at a sufficiently powered size? I would love to. This is why we just did this pilot study we had, because we have many mice and say, hey, let's give it a shot and let's see. Because there's a lot of hype over naddemen, and we saw this.

Love to do it at a much higher level, because my question, which might be a disruptive question, is, like, what if you have a small tumor that you're unaware of, like, in the pancreas or in the colon or in the lung? Could nad over time, day after day after day, could favor that glycolytic flux to that tumor and increase the growth? I've never looked because it just kind of occurred to me. When you had that slide up earlier. Earlier, and you showed the mitochondrial slide, occurred to me that you have that lactate escape from the tumor.

Peter Attia
Hey, this would feed it. But has anybody in the literature examined this question? It seems like a very reasonable question to ask. There are a couple studies I think once I review is more at the conceptual level. And this is what got me thinking, like, yeah, this is something that, for us, working in cancer metabolism, we look into this.

Inigo San-Milan
Obviously, one of the things that we have shown is that lactate is an oncometabolite. Lactate, we have shown, have a first paper, and we have like a good six, seven papers more to come. Working hard for three years looking into this. But we saw that lactate regulates genetic expression of the most important genes in breast cancer. We're seeing the same thing now with lung cancer.

And lactate, as we keep talking about this, is the mandatory byproduct of glycolysis. And as war saw in 1923, the characteristic of cancer cells, or most cancer cells, is the high glycolytic flux. But what struck Warburg was not the glucose itself, it was the lactate production. So anyways, we are showing that it's an oncometabolite. So if you have a high glycolytic rate in a cell, you're going to produce a lot of lactate.

You cannot clear that lactate, it's going to drive cell growth and proliferation, as we're seeing. And in fact, we're now blocking lactate production, both through genetic engineering as well as DCA, for example. And we're seeing that cancer growth and proliferation completely stops within hours. Now, that poses an interesting dilemma, which is exercise would increase your capacity for clearing lactate in the long term, but in the short term raises lactate. So it begs the question in a cancer patient specifically, what's the net impact of exercise?

This is what we're working on. The hypothesis with my colleague George Brooks, he's shown that acute response to lactate, it increases overexpressions, about 600 something genes. I forgot right now, all these genes are involved in cellular homeostasis and in the benefits of exercise. We know very, very well through his work that lactate is a signaling molecule. Now, the question is like we know this at an acute exposure, which is exercise, you do exercise, boom, boom, boom, you're out.

But cancer doesn't do that. Cancer accumulates lactate and it keeps accumulating. This is the main responsible for the tumor microenvironment, which is acidic. And the more acidic the tumor microenvironment, the more metastatic the cancer is and the more aggressive, like the more glycolytic a tumor is, and this is very well documented, the more glycolytic the tumor is, the more aggressive it is, and the more lactogenic that is, more lactate the tumor produces, the more aggressive it is. Now, why is that lactate accumulating?

That's what we need to try to find out. But we know that that is not acute anymore. It's chronic exposure to lactate can exercise, counteract that? When we see that exercise might be beneficial for many patients, but again, going back to the right intensity, we know particles which are exosomes, there are microvesicles in the body. They are mainly responsible for metastasis.

We have seen that. And this is another publication we're going to have in breast cancer cells and lung cancer cells. We are looking at the protein content and the micro rna of those exosomes released by these cancer cells. The information that they have. If you were to genetically engineer a molecule that can inject it into a tissue and transform into cancer, you would replicate an exosome.

It has all the components needed. On the other side, muscles also release exosomes. And this could be one of the benefits of exercise as an organ and the crosstalk between skeletal muscle in many organs. We know that if you have very good muscle health, your health, overall metabolic health is going to be good. Could you be releasing great exosomes?

They're very pro oxidative, which counteract the glycolated phenotype of cancer. And could those exosomes travel directly to the cancer cells and counteract that and penetrate into inside the cancer cells and transform the glycolytic phenotype of the cancer cells into more oxidative phenotype and keep cancer at bay. We don't know yet. We're suspecting that we're scratching the surface of something that potentially could be very interesting thing to understand better the effects of exercise as well as novel therapeutics. The deeper I go in the rabbit hole into all things that relate to longevity, the more convinced I am that if you're going to rank order things, if you were forced to rank order things, there's nothing that ranks above exercise as the single most potent tool or agent we have to impact longevity.

Peter Attia
And yet, paradoxically, in the acute setting, exercise seems to do everything incorrectly. In the very short, acute setting, if you look at it in that narrow context, exercise does not appear to be giro protective. But of course, when you look at the chronic impacts exercise and what's taking place after the bouts of exercise, the data seem undeniable. I want to kind of pivot from exercise a bit into a subset of that, which is something you published this year in long COVID patients. So we'll link to the study so people can see it.

But you demonstrated that in people with long Covid, even previously healthy people, they basically, from a mitochondrial standpoint, end up looking like people with type two diabetes when they're done in terms of fat oxidation, lactate production. So first question for you is, what fraction of patients recovering from COVID do you believe are susceptible to that phenotype? Everything is started by National Jewish Hospital is probably not always with Mayo Clinic competing for the top one pulmonology hospital in the country. You have these people with long Covid who are struggling. They go up the stairs and they can't breathe.

Inigo San-Milan
So the first thing they do is they go to different doctors and they end up going to this top hospital. So they do a pulmonary function test and it's completely normal. Then they, okay, the next species is because Covid also affects the cardiac muscles. Let's look at the cardio function. It's completely normal.

They're very good at this hospital where they do metabolic testing, they do CPET testing. That's how I call it, medically, right? Physiological testing. And they even do lactate. I've been interacting with them a few times.

So they do lactate as well. They contacted me and said, inigo, look, we're seeing these patients. We have 50, 25 of them. They had previously underlying conditions. The other 25, they were normal people.

And in fact, most of them, they were morally active. Some of them, they were doing marathons, triathlons, the average is 50, so they're not very old either. But their pulmonary function is completely normal and cardio function is completely normal. So we suspect that there's some metabolic issue here. So they send me all the information, the raw information, and I applied the methodology that we've been discussing, looking at fat oxidation and lactate production as a surrogate for metabolic function and metabolic flexibility and mitochondrial function.

And I was shocked because they were significantly worse than people with type two diabetes and metabolic syndrome, which could explain why these people cannot go up the stairs and where before they were doing marathons. Now, what are the mechanisms? We know that viruses, multiple viruses, are known to hijack mitochondria, their own benefit for reproduction. Could Covid do the same thing? We are suspecting it and we're trying to understand that at a more cellular level.

Now, unfortunately, the majority of this long Covid, because, as you know, there are people with long Covid syndromes that within weeks, months, they improve, they go back to normal. But there are a handful of people that I am assuming they're going to be growing that after one year they haven't improved a bit. This is the concern. Like, can we use exercise as a therapeutic way to stimulate mitochondrial function if in fact there's a mitochondrial dysfunction, which is severe, because if that's the situation, it's going to expose these patients to multiple diseases. So this is an area of concern.

Peter Attia
And this isn't talked about as much as what I think people initially spoke about here, which is basically myocarditis. Now, of course, we know that the risk of myocarditis is actually much higher in young males through the Moderna vaccine than it's ever going to be with COVID But the rate with COVID is not zero. It's. I believe it's 2.3 cases per. It's going to be a big difference.

I think it's 2.3 cases per hundred thousand of people with COVID are getting myocarditis. Most of those are transient. They recover. Not all of them are. So a subset or not, but this mechanism would be distinct from just myocarditis.

Myocarditis, of course, speaks to the inflammation of the cardiac muscle. That would explain depressed ejection fraction. But what you're describing is a far more diffuse problem, is a global insult on the mitochondria in the skeletal muscle. Correct? That's what we suspect from this data, which, again, is indirect, from the indirect colorimetry in the lactate that it points out towards mitochondrial dysfunction.

Inigo San-Milan
So that's what we need to do now, biopsies to understand this at a better detail. What the heck is going on? Could be at the micro perfusion level, too. It might not be at the muscle per se, might be at the microfusion in the blood, in the capillaries, meaning. Something like microthromboses that are preventing perfusion and raising lactate that way.

Could be. Could be. That's what we need to find out. But we know from other viruses that they hijack mitochondria. They interfere, especially with the fission and fusion processes.

Some causes increase fission, some other causes increase fusion, some other causes increase elongation. So we know there's a wealth of studies out there from virology showing that, yeah, many viruses and bacteria, they hijack mitochondria. They disrupted significantly, but most of the times, like myocarditis, it subsides, it's restored shortly after the symptoms are gone. Why this virus is different? That's what we are trying to understand, why people after one year.

By the way, you know, most of these people, they had just normal, mild course of COVID They were not hospitalized, they were not in the ICU. Any evidence or inkling that if people go back to exercising too intensely following recovery, it could exacerbate this problem? And do you have a sense of which strains this was? Your work would have been predominantly alpha and not delta and obviously not Omicron, correct? Yeah.

Even a mixture between the original variant and delta. So not Omicron. So in this population, which, again, is presumably mostly alpha, maybe some delta, what was the distribution of male and female? Female? We have 35 females and 15 males.

Peter Attia
More female predominant, which, again, maybe is too small a sample to know. That could be more an indication of who's seeking out. And again, we don't really know the denominator. We don't know what this represents. Is this one in a hundred thousand?

It could be one in a million. If this was everybody that's reporting it at the time, our guess is this. The rare event can last that long. But we're talking about millions of people infected, right? If it's one in a million, we're talking about a population that is going to need help.

I want to go back to just a few other questions that we didn't get to, so not necessarily in any thematic order. What's the relationship between, or how predictable, I should say, is the relationship between zone two, as defined by maximum fat oxidation and Vo two max. So if you run somebody through a cpethe and you figure out that their Vo two max is at four liters. How predictably can you say at x percent of that, you will be at maximum fat oxidation. There's another study that we're preparing, the manuscript with 225 subjects, where we look at fat oxidation, Vo two, and the relationships going back to the same thing we tend.

Inigo San-Milan
And historically, the research studies with exercise have been done based on vo two max. That's been the parameter to prescribe exercise. How many times we read x amount of subjects, they were exercising for six months at 60% of Vo two max or whatever. Now, that's another thing that I've been thinking of years. And by the way, when they say that, do they mean 60% of the heart rate that produced Vo two max, or 60% of the power that is their max power at vo two max?

Peter Attia
Yeah. I mean, there's so many different ways you can do this that I've always found it. You have to get into the methodology very closely. I agree. I agree 100%.

Inigo San-Milan
And this is where I think we need to dial in things in better, because, yeah, 60% of the power output, the intensity might be translated into power output. 60% of v two max. And then you translate into power output, or you translate into heart rate. Or is it 60% of the vo two? So, for example, if somebody's four liters, vo two, and then they hit that at 300 watts, would 60% be 2.4 liters, which, of course, is not a very helpful way outside of a laboratory to prescribe exercise to somebody.

Peter Attia
Or would it be 180 watts, which is 60% of the 300 watts? Yeah, exactly. I think that normally, these studies, they look at, where do you hit 60% of the two max? How many watts is this? Or what's your heart rate?

What's the wattage that corresponds to 60% of your max? Vo two. And in our study, what we are seeing, and this is what. Because I've been curious about this, because we look at the cardio respiratory adaptations to exercise and we look at the cellular adaptations to exercise, do they really correspond? We know very well with athletes, you can improve tremendously at the cellular level, but not at all at the cardiorespiratory level, at least based on Vo two max, which is the representative of the cardiorespiratory adaptations to exercise.

Inigo San-Milan
One example that I always give when I give talks, an athlete who used to be an average professional, the VUE two max, was 72.3 or something like that, and then two years later, he is a very good professional. The VUe two max is the same, but the lactate levels were incredibly better. I forgot a five watts per kilogram. He was at five millimoles, and now it's at 1.7. This is where the magic happened to this specific athlete.

It was at the cellular level. We see this across the board. Right. CO2 max at the elite level does not come close to predicting performance, not at all. This is why we're putting together this study with all this population of different from people with metabolic syndrome all the way to the France athletes.

So longitudinally, we see that, yeah, sure. Vo two Max corresponds with fitness in the same manner that watts corresponds with fitness. So we can also imply that instead of doing a Vo two max to look at longevity and fitness, we can also do a power test or a speed test and a treadmill, because we're going to see the same thing. Those ones who are very poorly active, they have a very poor fitness. They're going to have a lower Vo two max, they're going to have a lower power output.

They have a lower speed, lower lactic cleanse capacity. Vo two max has been forever a great surrogate for fitness, cardio respiratory fitness and longevity. But we wanted to see if, in fact, it's really that specific. So in our study, we see that people in different categories are the same Vo two max. They might be in different metabolic states.

So some people at the same Vo two max might be oxidizing a lot more fat or a lot more carbohydrates. So that means that does not correspond to the same metabolic status. I would have thought that most people, by the time they're at vo two max, they would be disproportionately carbohydrate. So really, you're just saying how much fat oxidation still remains there is really what you're saying. And I'm assuming a very untrained person has zero fat oxidation by the time they reach vo two max, whereas a more highly trained person would still have some amount, they might still be at 0.2 or 0.3 grams/minute yeah.

For example, we see that, like a sedentary individual, at 75% of the vo two max might be around three millimoles, whereas a world class athlete at the same percentage of vo two max is about one and a half. So metabolically, they're different, yet the vo two max is the same. So if we prescribe exercise based on vo two max, we might not do things correctly. And the same thing with carbohydrate at a 75% of a vo two max, like a sedentary individual oxidizes about 2 grams/minute where an elite athlete oxidizes about 3 grams/minute so that's a significant difference. And we also see it at 50% already.

So this is why longitudinally they correspond quite well. And same thing as fat oxidation. Fat oxidation at a 50% of vo two max is about 75% of CO2 max. 0.23 in sedentary, it's 0.6 in an elite athlete. We look at the different intensities, for example, that an athlete that can have one millimole of lactate within the same group, not just comparing group, but we can see that someone within the very same group, whatever the category they are, the lactate and the vue two max don't correlate.

The correlations are sometimes using 0.2 or 0.1 or 0.3. That's the r squared, you're saying? Yes, no correlation, very poor correlation. When we talk about individual groups, when we look at specific one parameter, which is lactate with the vo two max, it doesn't really correspond. So anyways, this is what I think that we have learned a lot over these last decades, where we can really pinpoint more at the cellular level to improve metabolism more than at the cardio respiratory function, which is very important.

Absolutely, they both are going to improve, but I think that if we want to prescribed exercise, it's going to be more specific. If we look at cellular surrogates like lactate, like fat oxidation, for example, then looking at vo two max or mets, I mean, don't get me into there. That's very prehistoric in my modest opinion. I don't want to offend anybody, but the whole Met concept used for exercise prescription. It's hard to swallow in today's times.

Peter Attia
Yeah, I was just about to say. I mean, it served its purpose in the 1950s. When we think about some of the muscle biopsy data again, this term of mitochondrial function, it's such an important part of longevity because it is one of the hallmarks of aging, is declining mitochondrial function. I used to explain to patients that the type of physiologic exercise that we're prescribing this zone two exercise, is the way to measure mitochondrial function. It's both the treatment and the test, but I'm guessing on the cellular level there's even more that we can talk about.

The last thing I really want to talk about today, because I know we've been going for a while, you've been generous with your time. When you get into the omics, when you start to biopsy the muscles. When you start to look at the mitochondria in a way that we can't do it in a regular clinical setting, what else are you seeing that's differentiating the healthy from the unhealthy mitochondria or the high functioning from the low functioning mitochondria? Again, I keep talking about papers. I wouldn't publish it, but we've been working for three years quite hard, and now we cannot continue doing this.

Inigo San-Milan
We need to start writing the papers, right? You need more postdocs, more graduate students in postdocs to help with the writing. But we have completed a pretty cool study and they're writing the manuscript now. Looking between sedentary and active, we know already there are a bunch of research showing at the cellular level the difference between people with type two diabetes or metabolic syndrome and active individuals, or even sedentary. We want to see also, or want to show that people who are sedentary, they already have problems, and we wanted to compare them with moderately active people who should be kind of how we should be as humans.

We looked into the mitochondria into mitochondria. We looked at their significant dysregulation at the mitochondrial level. Everywhere you look in the mitochondria, in sedentary individuals, you see a decreased capacity to oxidize, to burn glucose in terms of pyruvate, fatty acids, amino acids. You see a significantly decrease in electron transport chain as well all the complexes, and you see also a significantly decreased capacity in the transporters of different substrates. One thing that really caught our attention, and we think that this is something that we really want to emphasize and hopefully others in the future, is that we have identified that there is the mitochondrial pyruvate carrier, which is, as I discussed earlier, that's the transport of pyruvate into the mitochondria, which is dysregulated already significantly down regulated in sedentary individuals compared to active individuals.

Then we are matching it with the pyruvate flux, the oxidation itself. So both the transporter and the flux are significantly dysregulated. What does this mean? That's going to shuttle pyruvate to the other way. It's going to get in the cell, which is through lactate.

Exactly. Exactly. What are the implications of this? So again, these people don't have diabetes or prediabetes. This could be a healthy person who's not active.

And this is what, unfortunately, this being the model in most research papers out there, comparing the unhealthy with a sedentary health individual. I've been pushing for years that the model should not be the healthy sedentary individual because that is the intervention. As humans, we are meant to walk or to exercise, so we need to look at perfection, to understanding perfection. The intervention of human evolution has been becoming sedentary. And in fact, I had a hard time to get IRB to start this study.

I have a hard time with the committee to convince them that using active people as the gold standard to understand imperfection, that's the way to go. But anyways, what we see is that these people already, they don't have clinic, but, yeah, they have a significant downregulation. They don't have clinical signs. Clinical symptoms, sorry, they're not clinical symptoms, they're the healthy sedentary individuals. They don't have insulin resistance and they.

Peter Attia
Don'T have down regulation of glut four transporters, even hyperinsulinemia. Are they hyperinsulinemic when challenged with the glucose tolerance test? These people, they have no symptoms, they haven't reported any glucose tolerance tests. Normal people. And then they have a significant disruption in this mitochondrial pyruvate carrier, which might mean that the first door that might be jammed is that entrance of pyruvate inside mitochondria.

Inigo San-Milan
Most of the research in diabetes has done more at the peripheral level, if you will, glucose levels, more at the surface levels of the cell, the glut four, the insulin resistance, the pancreas release of insulin beta cells, et cetera. But what's the fate of glucose once it enters the cell? And this is what we're looking to this. And the fate is pyruvate. But what's the fate of pyruvate, as you said, very well.

Does it enter the mitochondria or is shuttle to or reduced to lactate? So I think that this is important to see because it could be a marker down the road, because, again, these people don't have clinical symptoms yet. They have a significant dysregulation in their glucose metabolism. So could this be 1015 years ahead of clinical symptoms and insulin resistance? This is more reason also to consider sedentary individuals to see, hey, they have a metabolic dysregulation already.

Same thing we're doing at the fat oxidation level, the CPT one and CPT two, the transporters of fat, they're significantly down regulated as well. So that means they're not going to be able to transport fat very well, which also matches to the fat oxidation itself. When we inject fatty acids into the mitochondria that are not oxidized well, so they all match as well. So they have this regulation already that is significant compared to motor active individuals at the glucose metabolism and fat metabolism. Then we see that many of these people, I mean, who have diabetes or metabolic syndrome, they have what's called intramuscular triglycerates, the fat droplet, and it's adjacent, right by the mitochondria in elite athletes.

It's also there, that fat droplet, but it's very active because about 25% to 30% of the fat oxidation comes from that fat droplet adjusting to mitochondria, which it could probably isn't an evolutionary mechanism to not rely on the adipose tissue, which might take time and have something right away there. So when you say it's metabolically active, the difference between the intramuscular fat of the athlete and the intramuscular fat of the person with type two diabetes, is it the flux, then, in the person with type two diabetes? It's a static source of fat. In the athlete. It's constantly turning over and being oxidized and replenished.

Exactly, whereas in this population, it continues to grow. My colleague Brian Bergman from the university is working a lot into the content of what's inside these fat droplets. But one thing that we know is they're very high in ceramides, and diglycerides, and especially ceramides, are key in the atherosclerotic process. Atherosclerosis, it's a hallmark of cardiovascular disease. Ceramides are key for this process.

Historically, it's been thought, and it's been shown that ceramides come from the liver. They're released. But we're seeing that these intramuscular triglycerides are high in ceramides. So could this be a connection between also cardiovascular disease and type two diabetes. In the high turnover, high flux?

Peter Attia
One, you're not accumulating them as much. Yes. People who end up having type two diabetes, they accumulate fat droplet athletes as well. That's the athletes paradox. But athletes, as you said, they keep turning around, and it's very active, whereas people with type two diabetes or obesity, it keeps growing, it releases pre inflammatory mediators, and it also is high in ceramides, which are key in atherosclerosis.

Inigo San-Milan
So this is where we're trying to establish the connections between type two diabetes and cardiovascular disease at the mitochondrial level as a nexus, because we know that about 80% of people with type two diabetes, they also have cardiovascular disease, and vice versa, which is what we call cardiometabolic disease. So could the nexus of all that mitochondrial impairment. That's what we believe. Well, what I take away from this is we're probably gonna have to do a third podcast in a couple of years because there's going to be a lot of data that's going to be published then that isn't published now. There's going to be a lot more questions that we're going to have answered.

Peter Attia
Again, I'm still really yearning to understand the effect of metformin in terms of pure mitochondrial function and performance in a trained individual. So, as always, I can't thank you enough for your generosity of insight and look forward to talking tomorrow when we have a call about some other nerdy stuff we're going to get into. Thank you so much, Inigo. And also, congratulations on the remarkable success of your team and Pugachar, who's an amazing cyclist to watch. He's got everybody very excited about the Tour de France again.

Inigo San-Milan
Well, thank you very much, Peter. All the listeners, I really appreciate what you do. The first time I met you, we're two and a half hours talking about mitochondria. And at first I thought like, this guy's crazy. There's nobody out there who's going to be interested in listening to two and a half hours about my mitochondria and metabolic health.

You showed me. Yeah, the concepts are out there, and I was in a moment where I was not many people seems interested in this, and you were already an inspiration for me to continue doing this. And the remarkable work that you're doing to educate people and inspire people, it's transformational. So I really appreciate the invitation, which is an honor. Thanks for being with us today.

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Peter Attia
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