The Limits of Human Energy Expenditure with Herman Pontzer PhD and Drew Best PhD | Koopcast Episode 157

Trail and ultra runners, what is going on? What's happening? Welcome to another episode of the KoopCast. As always, I'm your humble host, Coach Jason Koop. And this episode of the podcast focuses on the limits of human metabolism and how those limits might ultimately be the deciding factor on what the upper limit of ultramarathon performance actually is. On the podcast today to enlighten us is the dynamic duo of Herman Ponser and Andrew Best. Herman is a professor of evolutionary anthropology at Duke University, where he focuses on the evolution of human energy expenditure and metabolism. He is also the co-founder of the Human Evolutionary Ecology Lab, where he and his team study the effects of diet, physical activity, and modern environments on human health and disease. Herman's latest book, Burn, The Misunderstood Science of Metabolism, and a link to that will be in the show notes, is an incredibly intriguing read.

And in it, he explores the latest research on metabolism and challenges long-held beliefs about weight loss and metabolism, so much so that when reading that book and at times during this interview, you will be certain to have a head-scratcher or two, and if so inclined, like I am, head down the proverbial research rabbit hole. His work has been featured in numerous publications and media outlets, such as the New York Times, the Wall Street Journal, NPR, blah, blah, blah. You guys get the idea. But more important to our audience of ultramarathon athletes is how metabolic scope, or the amount of calories you can expend above your basal metabolic rate, might be the ultimate limiter of ultramarathon performance and influencer training. His colleague, Andrew Best, is a biological anthropologist and assistant professor of biology at the Massachusetts College of Liberal Arts. He's also a respectable endurance athlete in his own right, and Andrew is currently conducting a research project on ultramarathon and ultra-endurance athletes that further tests the limits of what this human metabolic scope might actually be.

This was a project that I just happened to be a subject in during my training and racing for the Cocodona 250 earlier this year, and so I decided to bring on Herman and Andrew to the podcast today to see what we can learn about their work and how it can inform our training and racing. All right, that's enough of me blabbing. I'm getting right out of the way. Here is my conversation with Herman Ponser and Andrew Best. Thanks, you guys, for coming on the podcast. I appreciate it. And especially for Herman, if you're going to be on sabbatical soon, we'll try to get this out of the way as quickly as possible so you can go and write your next book and start getting on. Are you into it already? Oh, yeah. Yeah, yeah, sure. Yeah, you can't, you know, they give you a, well, you know, the deadline we set is next year, next December. So I've got plenty of runaway, but that's kind of good and bad because if you have a deadline that's way far off, it feels like you have forever, you know, and you don't really. So, but I'm into it.

Is it going to be related to the last book? Like some, some sort of tangential topic? It's another, it's another book about how your body works only now, as I'm just looking at metabolism, and we're looking broadly across all the different systems in your body. But it's again, the sort of evolutionary lens on how the body functions. And the key piece of it is there's a lot, there's a few books out there that try to do that already, but this is how your body works relative to everybody else's. Like why we're all different, how sort of individual physiology happens, not just how your brain works, but why some people's brains were different than others. Well, so this is, this will be a good launch point. And I told you I'd deviate from the, from the outline at some point. So we'll kick it off with that. How did the, how did the first book come about? Because it was wildly successful, you know, and this is one of those things that you pitched to, that you pitched to a publisher. And I, you know, I know a little bit about this world.

You pitched to a publisher and sometimes they're like, man, I don't know, like sometimes these science topics like don't go over very well, but like, how did it all come about? Yeah. I mean, I've been working in metabolism for, you know, 15, 20 years now. So it's material that I've been kind of generating myself, you know, over the years with, with research and, um, the, some of the surprising results from that, you know, kind of spark people's interest. And I had people reach out to me about, Hey, well, you should write that up for, you know, for a broad audience, either as an article, you know, a magazine article or maybe as a book. And so I got thinking about that. Um, and that kind of just snowballed into this opportunity to write burn and that's how that went. Well, go congratulations. Because you, you, like I said, sometimes those science books, they either go one or two ways, either they're successful or they're just not. And they end up, you know, sitting on the Amazon shelves, collecting dust. So Herman, good job with that.

Drew, take a second to introduce yourself and how you got involved in, in the mix here. Yeah, I don't, I was trying to remember, um, how I first approached Herman because I'm sure it was me. It was probably two years ago or something, but, um, so I'm, I'm a late bloomer. Um, I taught high school biology for 15 or 16 years, um, and went back to, you know, become an anthropologist during that time. Um, so most of my background is teaching and the research really is new to me in the last, you know, seven or eight years. Um, so I guess the things I'm into, uh, evolution of sweating, um, a dissertation project was all about variation and sweat gland density. How many sweat glands do we have? Does it matter? Um, spoiler, I don't think it matters. That's a different topic. Um, and really all along the way I've been interested in the evolution of endurance physiology, you know, why are we built to move, you know, the Dan Lieberman stuff, the Herman Ponser stuff. Um, and so I think at some point, uh, I probably reached out to Herman via Twitter or something with some question. Um, and we chatted a few times, but then I think it was probably when Joe McConaughey approached me, um, a year or two ago, I met him in a race, um, you know, quick tangent, uh, Joe's a super nice guy. Um, he obviously beat me in that race because he's very good and I am less good. Uh, and I'm chatting with Joe and his now wife Katie after the race, and they're asking me all about my running. And of course I'm pontificating, Oh, I've done this and that. And he never even told me,

you know, what his deal was. He had just set the record on the Appalachian trail. So I found that out later and I was like, Joe, how did we not talk about that? It's incredible. Uh, so he reached out and said, look, um, I want to get some, some data, you know, sorry, my dog's barking in the background. Uh, and, um, he said, uh, I don't know what data to get, but I'm doing these crazy things. Let's study it. And, um, I was thinking, well, I need a new research Avenue. Um, I was just about to take my current job, you know, my first faculty gig. Um, and it's, it's really teaching heavy. So I needed a research direction to go into, um, where I could collaborate with other people, do it mostly in the summers, do some writing, you know, during the semester, that's really all I have time for. So I said, well, Joe, I don't think I can do this stuff, but I know some people who can. So reached out to Herman and a few others. And here we are. Oh, sweet. So we're going to talk about the research project that, that, that I'm a subject in, and we can divulge into that data at some point, but why does ultra marathon and not, not just ultra marathon, but ultra endurance keep popping up in you guys's work? I mean, I know that it serves as a blueprint for a lot of what we can understand about the human body, but in your, like just in your words, why is this so important to look at it through this specific ultra endurance lens? Yeah, I'll, I'll, I'll kick that off. So,

you know, we study human evolution in my lab, human metabolism as well, because, you know, the way that our bodies burn energy is where the rubber hits the road in terms of evolutionary biology, right? Life is a game of turning energy into kids. And so, you know, that's, that's really the nexus of evolutionary biology is where it's all, it all happens. So if you want to understand anything about an organism at all, you know, understanding how it burns its calories is a key piece of information, you know, because everything your body does from movement, of course, to growth, to reproduction, brains, immune systems, it all takes calories, right? So when we burn, when we measure energy expenditures in my lab or for any kind of research project, we're getting the whole budget for somebody's body, right? How many calories came in and how many calories went out. And so I've been studying metabolism from that perspective, that evolutionary perspective for a long time. And we've had some really fun results that made us rethink what we thought we understood about how metabolism worked. One of the key things was about 12 years ago, with Dave Reikland and Brian Wood, a couple of good friends and collaborators, we went to measure energy expenditures, daily energy expenditures, how many calories your body burns every day, with a group of hunter gatherers, that's a community called the Hadza. They are in northern Tanzania, they don't have any domesticated crops or animals or machines or, you know, vehicles or electricity. They live in grass houses in the middle of Savannah, and they get more physical activity in a day than most Americans get in a week, right? And that's the

kind of lifestyle. I mean, we're all modern humans today. There's nobody who's sort of stuck in, you know, nobody's a time machine. But if you have if you have a culture that has those kind of elements to it, that you're hunting and gathering, that's a way to ask the question, what does hunting and gathering do to our bodies? How do our bodies behave work in that kind of an environment? Because that's the kind of environment we evolved in, right? So as an evolutionary biologist, human evolutionary anthropologist, you know, that's the kind of thing I'm interested in. And so we went there, we measured daily energy expenditures with this technique called doubly labeled water, which is this really accurate, reliable technique for measuring total calories burned over about a week long period. We knew going into it, we'd see really high expenditures because like I said, that these men and women are really physically active. It takes a lot of walking and other work to make a living in the Savannah, right? With literally hunting with bow and arrow or digging, you know, wild tubers out of the ground. These people work so hard.

They work for a living. They work for a living, literally. They work for a living, yeah. That's exactly right. Very few of us actually do. No, that's exactly right. And so, you know, and that's again, that was kind of for an evolution perspective, that's the data point you need. And the huge surprise was that their total of energy expenditures are the same as typical Americans, right? So super surprised by that. They're burning the same number of calories every day as folks in the U S Europe, Japan, other industrialized countries. And that tells us what the body is doing to the really phenomenal here that we hadn't appreciated before that lifestyle kind of doesn't push things around like we think it does that, you know, at least up to some point, up to some pretty high level of activity, your body can adjust, you know, the more active you are, it seems to change the way your body burns calories more than it does the number of calories you burn every day.

And of course that constrained view of energy expenditure is a big surprise. It changes the way we think about how exercise affects our bodies, affects our health and lifestyle affects metabolism, energy burned. Um, but then the obvious question is, well, are you telling me, right? This is the question I always, are you telling me that Michael Phelps, you know, swimming, God knows how many meters he swims a day or a week or whatever. Are you telling me an ultra marathon runner who's running a hundred miles a week or whatever it is, are you telling me really that they're burning the same number of calories every day as somebody sitting behind a computer? Uh, and so the answer is no, there must be some limit, right? There must be some limits on this constraint. There must be some metabolic ceiling or maybe there's a metabolic ceiling. Maybe you can push, maybe anything's possible. If you push hard enough, you know, we don't know. So like this question about what are the metabolic limits, what are the limits of endurance? How does it all fit together? Uh, that becomes the obvious set of questions to ask. And that's why I love this research so much because it's, it's kind of, for me, is this the obvious next thing to ask? Okay, well the body seems to adjust to lifestyle. What are the limits to that? How does it actually work out? And people who are really pushing the body to its extremes. And the, the ultra marathon crowd, the ultra endurance crowd happens just to be very good candidates for that. Um, and we're going to talk a little bit about the research project that Drew's, uh, involved in a second, but to set this up, since we are going to

talk about human energy expenditure, and we're going to have predominantly a lay audience here, let's give a freshman level overview of what the buckets are in terms of how we can choose, how, how we can choose or how we have to spend our daily calories as humans. So you've got 37 trillion cells and every one of them is a little microscopic factory. That's bringing stuff in, dealing with it and putting stuff out, right? It's every, every cell in your body is active every day, chugging along, burning calories. Um, and we can think about each system in your body then as sort of a department in this big business that we run, that's our body, right? The kind of thing about your body as a business resources come in, work gets done and all that, that process, that energy burn on that is, is what you call your metabolism.

And so every system in your body is burning calories, right? And so if you're at rest in the morning and you're just completely laying there flat, not stressed out or anything like that, your organs themselves are burning what we call your basal metabolism. That's like all your departments at their lowest level of energy expenditure. So your brain digestion, um, immune system, all that stuff at its lowest level of expenditure, all of that just background baseline stuff. Um, takes it, they use this up about 60% of your energy, 70, 60, let's say 60% of your energy every day for the typical American, um, is most of it spent on that. The rest of the energy you burn every day is a combination of things like movement, exercise, um, even muscle activity that you wouldn't think of in terms of like standing up, right? The postural muscles take energy. Um, and then things like thermal regulation, staying warm or cool, uh, stress has energy costs, right? Your organs themselves have a kind of circadian rhythm, like kind of like they're more active during the day than they are at night. And so there's, there's also the sort of less well understood component of, of fluctuating, circadian changes in, in cell activity. But those are the big buckets, your organs at rest, your muscle movement, and then some in between stuff that's, that's a little bit harder to get your hands on. And so what's the theory then, since you've been studying all of these extreme

populations, what's the theory in terms of how much energy expenditure can we either fluctuate or live by day to day? You can, you're probably going to be able to describe it better, better than I'm saying. Yeah. So, so the typical American burns, you know, between 2,400 and 3,000 kilocalories a day. Men burn about 3,000 kilocalories a day. Women burn about 2,400 kilocalories a day. There's variation around that. Most of it's based on size. You can be more physically active and it doesn't necessarily change that number. Right. And so what's happening? Well, if you're more active, it seems like you're, we're spending less energy on all the other systems that our bodies are active with. Right. All the other systems that our bodies burn calories on. And so we're, we're actually trying right now in my lab to figure out what all those sort of levers you can pull to, to take, take energy away from this system because you're using it on activity rather than on, let's say, immune system.

Here's what we know now. We know that if you are a runner or any kind of athlete, you're burning more energy on physical activity than if somebody was sedentary. And that's good for you. You should do it anyway, even if it doesn't change your total calories burned. But people who exercise regularly have lower levels of inflammation. So inflammation is immune system activity that your body doesn't really need to do. You know, chronic baseline inflammation as high as is bad for you. And that's your immune system sort of running unnecessarily. Those are calories you don't need to burn. People who exercise more don't respond as dramatically to stress. So their heart rate goes up less and it comes back sooner than someone who's, who doesn't exercise. So you're saving calories that way. We think reproductive hormones seem to be in a more, in a healthier place. And so like testosterone, estrogen levels are not, they're not, you can overtrain to the point that you can actually suppress them to an unhealthily low level. But you know, for people who exercise, they tend to be in a healthier range than the sort of higher ranges that you see in sedentary people. So that we can kind of see where the body is saving energy. We don't have the story sorted out yet. So this is sort of in process work. And there are going to be a lot of athletes out there that listen to this and say, wait a minute, you're telling me that whether I sit on the couch and watch Netflix all day, or I go do a 50 mile run, you're telling me that I don't need to eat it. I can't eat anymore,

because that's usually people's excuse to, you know, go out and run. And so they can have an extra, you know, helping of Thanksgiving turkey, since we're recording this just after the holidays. So explain that nuance to people, because that's what everybody's thinking right now. That's right. So the more physically active you are, the more you exercise every day. It doesn't seem to change the total calories you're burning very much. And so it really doesn't give you a lot of extra cushion to eat more, right? Or, and it won't affect the extra cushion that we're all carrying. That's the bigger issue, right? Exercise ends up being a terrible way to try to lose weight. Um, it's great to do anyway, but we've done this for a long, long time, not just my work, but we've done this for decades, that exercise isn't a great tool for weight loss. Um, and that's probably one of the reasons why is that you're, you know, there's other things that go on too, but one of the things that happens is your body adjusts to your new lifestyle and you're not burning as many calories as you expected to based on your exercise program.

So let's enter how we are actually trying to figure this out. Right. And, uh, we'll, we'll, we'll point to some more recent work that drew is kind of undertaking right now. Do you want to take a moment and just set up the study that you're looking at right now, based on this, like Genesis of talking to string being Joe and coming up with this idea that we're going to study ultra marathon runners? Yeah. Yeah. So to piggyback on a few things Herman said, um, so why ultra marathoners? Um, I guess one is because, uh, Herman and, um, I think it was a Caitlin Thurber paper, right? It's sort of the big paper that, um, for me at least has kind of laid the groundwork for, for what we're doing here. Um, so they found a pretty strong relationship between how long you're putting out some kind of metabolic effort, right? So that can be running say, and basically how many calories you're able to burn during that time. So the longer that you're going all out, um, you know, the slope goes down. So basically, uh, you can, so we call it metabolic scope. We should probably mention that at this point. Right. So Herman talked about your BMR, your, your basal metabolic rate. That's the total calories it takes to run your organs and, you know, stay alive. And the energy that you spend on physical activity is the top slice of that pie, right? So metabolic scope then is your total energy expenditure that you spend in a day.

So basal metabolic rate, the cost of digestion, uh, fidgeting, walking. And if you're a runner, all the running you're doing that total number divided by your basal metabolic rate. So it's a multiple of, of your basal metabolic rate. So it's, it's really a measure of how much extra physical, how much extra calorie burn you have over and above your basal metabolic rate. So what, uh, Herman and Thurber's research really pointed out is that there's this really strict relationship. It seems like between how long you're doing some kind of physiological effort and the calories you can burn or the metabolic scope you can sustain. So we're looking at ultra runners for one reason to get more data points for that regression, right. And to better elucidate that relationship between the event duration and, you know, metabolic scope, really the metabolic ceiling that you're, you're limited to. And the other reason is, you know, to start testing some of these to, to, I should say further test one of Herman's big questions, which is what are the limits of human energy expenditure? What is that sustainable metabolic ceiling? You know, um, how many calories can a person burn every day before they start to dig into, you know, their fast stores and, you know, breakdown muscle protein and stuff. And that becomes relevant to ultra runners.

Um, but we look at ultra runners because hopefully they're doing a big training volume, right? So these are people who are sort of dedicating their lives as you guys really do to the pursuit of really maximal energy expenditure. Um, so for the, for the same reasons that we need to be careful using modern athletes as a proxy for, you know, here's how humans evolved. I mean, we're fairly unusual, right? Uh, there's probably a self-selection going on. Um, you know, we, we tend to be from Western industrialized countries. We tend to have enough time and money to devote to training unlimited, you know, nutrition, all that stuff running way more miles than any early human ever would have. Those same reasons also make ultra runners kind of perfect for asking these questions. It's almost like a natural experiment where we've removed all these other variables that, that could be limiting energy expenditure. And these are people who might be butting up against whatever that absolute limit is, all other things sort of being removed. So that's why ultra runners, um, And it's elective too. That's the other thing. Like we're choosing to, we don't have to, because we don't have to dig tubers out of the ground. Herman, to your, uh, point earlier, we're choosing to do this like out of, you know, whatever I like doing it. I want the challenge or whatever. I guess my point is, is, is like, it's voluntary. Yeah. And it's just to jump on what Drew said there. So to put some numbers on this metabolic scope, this metabolic ceiling that we think we all live under, uh, if you run the Western States hundred, right. I think the fastest people

do that in 20 or 22 hours or something like that. And for that time, but that 20 to 22 hours, you can burn about eight to nine times your metabolic scope. I think it is the key is the number. Um, you come down to the toilet of France, which is 24, 28 days long. I think it's changed a little bit over the last couple, uh, last couple of decades. Anyway, for that long, right. About a month, you can do four and a half times your basal metabolic rate. Your metabolic scope is 4.5. And so if you go out further, we had people who ran from Los Angeles to Washington DC over five months, they were burning about three to three and a half times their basal metabolic rate for that amount of time. And the longest duration, highest expenditure thing we've ever measured is pregnancy, which isn't an ultramarathon event, but it kind of is way harder, way harder than we've got to give the ladies some credit since this is all dudes on this call here.

Absolutely. Absolutely. And so, you know, when I said this to my wife, we got, I've got two kids and I was like, guess what? Women in pregnancy are burning the sea. It's just as hard as a sort of France. And she was like, yeah, no, no kidding. It's like no shocker. Yeah. Uh, but you know, but for something like the tour de France to Drew's point, we know that at some, in some way that must be a limit because if you could burn, let's, I forget what the number is exactly from the tour de France city, but let's say it's 4.5. If you could do 4.6, you'd win the tour de France by three days. Right. Right. If you could do Western States at 12 times your basal metabolic rate instead of eight, you'd, you'd do in 15 hours. Right. So like, you know, from the people who are like yourselves, you're pushing it so hard on these ultra marathon events, they are the perfect test of, of this limit because it really does, you know, cause obviously people would love to put, to break that ceiling.

They'd love to be in the space that we haven't measured anybody yet. That's above the ceiling. So, so how are I just, yeah, yeah. Go ahead, Drew. I just wanted to pick actually something Herman said, I think might be really interesting to point out, and this might be contentious, but, um, so I feel like in, in, in endurance performance, especially the longer the distance, it's really a game of who can expend more calories, which we don't usually think of it that way, but I think differences in economy or efficiency between athletes, uh, are probably not sufficient to really explain differences in performance over a really, really long distance. And if any physiologists are listening and I'm totally wrong, write in and tell us, but so it's as, as Herman was saying, you know, the difference between a metabolic scope of 4.5 and the Tour de France and 4.6, that person who can maintain a 4.6, uh, that really would be the key that it really seems to be, that is, that is the limiting factor.

The longer you go, it's not, you know, um, muscle damage. It's not VO two max. It's not lactate threshold. It's nothing like that. It's actually about expending more calories. So a lot of the training you're doing isn't just to make yourself more efficient. It's actually really just to develop a bigger sort of metabolic engine, not in terms of oxygen consumption, but in terms of fuel substrate availability and the availability to just continue breaking down carbohydrates and fats. Uh, so it really is that metabolic ceiling. It really is about burning more calories, which is not a way we often think about it. Well, and once again, I'm coming at it from a coaching perspective, right? The looking at what the, an athlete's limiting factors are in any type of endurance endeavor is one of the, the very fundamental starting points of trying to analyze what you should actually do with that athlete. What kind of training should you do? Should you run long? Should you do sprints? Should you do this type of interval workout? Should you train five days a week or seven days a week or a hundred kilometers a week or 200 kilometers a week or whatever? All of those decision points come back to what are the athletes limiting factors and how do we prepare the athlete to overcome those limiting factors? So this is kind of the meat of why I wanted to get you guys on the podcast, because if, if you're coming at this from the perspective that the limiting factor is the, the amount of energy expenditure, we can tailor training and interventions around that very, I, at least I would think that we can

tailor training around that very, uh, very specifically. So with the, with the group of, let's set up the study that you're doing right now, right? So the, the one that, the one that I was, that I am a participant in, how are you getting to try to solve some of this problem? Why don't you walk the listeners through what you're actually looking at and what you found to date so far? Um, okay. So we started with Joe, um, Joe McConaughey ran the Arizona trail about 800 miles, uh, maybe a year and a half ago. Um, and so we gave him the doubly labeled water dose and we're able to, by, you know, collecting urine samples every day, um, throughout the course of that effort, uh, he and his crew packed those on ice, sent them to Herman's lab. Um, and we don't need to go into the details of doubly labeled water unless you want to, but basically, uh, able to sort of work backwards, um, from the levels of the different isotopes in that doubly labeled water in those urine samples to figure out how many calories, um, he was burning every day. So, and that worked really well. We got some numbers on Joe. Um, we got some baseline data from Joe just during a 10 day period of normal life and training. We can talk about what we use that for later. Um, and then we just expanded it a bit. You know, I talked to Herman and we said, um, okay, how much, how much money do we have to support this? Um, we decided we can probably get data on what, maybe 10 to 12 ultra runners, you know, over the next year or so. So, uh, this past summer, um, Joe actually helped us

recruit some of you guys who ran the Coca Donut 250. And I thought, man, what a perfect event as, as ultras get longer and longer and more extreme, um, you know, these are the people we really want to get. So we got all that data from five of you who ran Coca Donut. Um, you know, we got some baseline data. Uh, I think one person, we still need to get that. Um, we got race data. How many calories you folks were burning during the race? And I mean, going into it, I, I tempered my expectations and yours. I remember saying, okay, there's five of you. There's no way you're all going to finish this because even in a hundred miler, what, I mean, I don't know what the dropout rate is, but I wouldn't expect five people to finish, you know, Western States. Right. Let alone, you know, the Coca Donut 250. So I'm watching the tracker, you know, the live tracker. I'm like, these people are all still going. This is incredible. So all of you finished. So we have, you know, all the data from that. Um, and then we just added one more data point. You know, we're mostly kind of limited by my time. Honestly, that's, that's why it's moving a bit slowly.

So I got one of my buddies, um, who set the record on the Appalachian trail for the state of Massachusetts, where I live. The trail actually pretty much passes right by my office out there. Um, and so we got his data from that effort. Um, and so that's, that's really the data set that we have at the moment. Um, hoping to add some more individuals this coming next, uh, summer. So that's what, that's what we have. Um, do you want to hear? I just interject because I want to kind of paint a picture of why we're going to this effort. Right. So, um, the, so we have basically from this, from the study that we did in 2019, we have this metabolic saline that we proposed is the limit of human ability that no human, this is, you know, this is the conjecture. This is hypothesis. No human can break this ceiling, right? You can do whatever you want, but your body will shut you down before you can spend more calories for a given amount of time than you're sort of permitted to by this metabolic ceiling.

Um, and we came about that idea by looking back to the literature and some of the data that we'd collected on a couple of, you know, this, this, uh, trans North American run. Um, and those data kind of cobbled together, right. From, from different studies over the last few decades, um, from the tour of France, from the Western States hundreds, from those kinds of events. And we, you know, we kind of piece this metabolic ceiling together, but as a scientist, you know, that if you, that's not the way you'd want to do it, right? What you'd want to do, if you really want to test this idea, there's a metabolic ceiling is to, rather than going back into literature and try to find old data and put it together, kind of cobble it together. What you want to do is design a study, you know, clear eyed looking forward and say, if this is the hypothesis, this is the ceiling we think really exists for humans, how can we punch through it? Or how can we test it and see, you know, prove ourselves wrong?

Cause that's what good science is where you're trying to prove yourself wrong. Um, and so that's why we're going to all this trouble because I'll, you know, if anybody can punch through that ceiling, it's you guys. So that's what we're trying to go and measure, uh, with all the folks you're recruiting for this study. And so what, what are you, what are you starting to find? Is that ceiling, uh, is that ceiling in fact a hard cap or are you starting to find outliers or anything that makes you question the previous hypothesis? I want to back up just for 30 seconds. That's okay. I should probably describe how we estimated long-term metabolic scope because we didn't measure that directly. Right. So first I'll answer your question just as a teaser and then I'll go back and explain. Yes. Uh, with our, with the limited data that we've added so far, you know, to Herman's ideas. Yeah, we are seeing a limit seems to be around two and a half times BMR. Uh, it's the same number that Herman's analysis found. And we're seeing that seems to be a limit still. So we're still, Herman doesn't have to rewrite his book yet. That's what, you don't have to make it, make it a, like a, you don't have to append it in any way so far.

It seems to be boring. You guys, you guys are disappointing me, you know, uh, science is more interesting when things don't work, but anyway, that's okay. Okay. Continue Drew. Sorry. Okay. Okay. So, so we, we have a couple of data points from each of these runners, right? We, we have how many calories they are burning, uh, really per mile for, for the Coca-Cola race and Joe's Arizona trail. And my friends, Appalachian trail, et cetera. And you know, the more data points we'll get, the better. And we have how many calories they're burning really per mile during their baseline training period. So I look back at their training logs and I say, okay, you were running, you know, this was your training volume during that time. This was your total daily energy burn. So we can establish this, this relationship between how many, you know, a person's total energy expenditure per day and how many miles they are running that day. Right. So we're making a simple regression equation.

And then looking back through their training logs, which was fun to see how you guys train. I basically, uh, am able to estimate using that regression equation, you know, cost per mile, what's the relationship between miles run and energy cost. Um, how many, how many calories you folks are burning for every month of a 12 month period that we looked at, you know, looking backwards based on your training logs. So from that, we get a metabolic scope for every month. And, you know, we can do this a bit differently. We could get a rolling metabolic scope and the results aren't that different. Um, so we find that the six people we're looking at so far, I think we have training records and all that from four or five of you so far, um, sustained metabolic scope averaged over a whole year as anywhere from 2.2 to 2.5 or 2.6. So even you guys who are doing this pretty intensive training, really intensive racing, you know, you're living a really high, high octane lifestyle, fully supported by, you know, ostensibly optimized nutrition, sleep training strategies.

Even you guys are not punching much above or at all above that 2.5 ish, uh, level. And how is there any relationship between where you can consistently kind of like live at, whether it's two or 2.2 or 2.5 times, uh, your, your basal metabolic rate and performance, meaning, is it advantageous to live closer to that ceiling or further away or undulate it? Have you found like any patterns with that? Or is that an open question so far? Open question. I would really hesitate to infer too much from this data set at this point. I mean, there've been a couple interesting things, but looking at only four or five people, you know, does not make a robust study yet. As far as those questions go, making comparisons between the people in this group. Right. But so we're sort of anecdotally with the small sample size we have so far, we're seeing that, um, the number of miles people are running in a given year, you guys doesn't really have any relationship to the metabolic scope that you're sustaining. So I know I'm not directly answering your question and we should come back to that, but so some people in our study so far seem to be running more miles at a lower metabolic scope. And a few of you are running more miles at a higher, at a lower metabolic scope and vice versa, whichever I didn't say. So basically some people are doing more with less, right? Some people are training more at a relatively lower energy burn.

Um, now what we're not measuring are the, you know, we have a BMR estimated with a really good equation from Herman at all. Uh, but we're not measuring sort of non-exercise energy expenditures during these people's day. So it's possible. I mean, I asked all of you, you know, is this the bulk of the physical activity you're doing, but maybe one of you is, you know, kayaking an hour a day. You didn't tell me, you know, I mean, trust me as a coach that happens, that happens all the time. People like never update their training logs a hundred percent. They always like hide a few miles and a few activities in the background and don't sync their watch. So yeah, you're, you're for sure getting that. So that's why it's important to get a bigger data set, right? Yeah. I would say, you know, uh, that's exactly what I would, well, so we're too early to have, you know, good training advice or anything to tell you guys that you don't already know working with these athletes day in and day out. Uh, but here's what I think is really exciting about this research in terms of the way that that will, this could go. Um, you know, why is it if this 2.5, 2.6, whatever it is, if that 2.5 ish ceiling is there on how many calories you can burn every day, uh, what happens as you get, as you get closer to it? Well, one possibility we think is that if you go past it, right. And you go past it for a long time, you're in overtraining world, right? And this is, this is reds and this is overtraining syndrome or whatever we want to call it now. Uh, and you

know, the symptoms you would predict. So remember we started off saying, it seems like your body can adjust. If you're more physically active, you spend less on other stuff, right? Well, what happens when you take it to the extreme? What happens when, you know, not only are you not having inflammation anymore, but you've actually cut down your immune system activity so much that it's bad for you. And you aren't recovering from a cold or you aren't recovering from whatever, right? What happens when your reproductive hormones don't just get kind of turned down a little bit in probably a healthy way, but actually get turned down so much that, you know, you get hypogonetic, uh, training, overtraining syndrome like Anthony Hackney's worked on. You get the classic female triad, women stop cycling. And, you know, so there are obviously, you know, kind of pathological consequences of, of spending so many of your calories on training that your body doesn't have enough calories to spend on all the other stuff it needs to do. Uh, and so, you know, we're kind of, I think, I hope the, you know, the utility of this work is we're going to be able to figure out where that is and help maybe help people understand it better, maybe be able to, to sort of structure their training better around that.

I think that that's the, probably the most relevant point for athletes to take home is that there is a ceiling, a long-term ceiling, and at times you can eclipse it. Like you just mentioned, the Western States, 100 tour de France, you're going on a normal, you know, training run and things like that. But when you look at things over a long-term perspective, months and years, this hard cap is something that needs to be adhered to. Otherwise there are a myriad of deleterious things that can, that, that can happen. And it's just not sustainable from any aspect, right? And you're coming at it from kind of the most fundamental evolutionary aspect. Let's, I want to dig into that a little bit more, but before we do so, I think we need to bring this into terms, like, like almost a really practical, relevant experience in terms of what does that look like on a day-to-day training perspective?

If somebody just goes out and does a training activity, what is that going to be to bring them to 2.5 to 2, to 2.6 times their basal metabolic rate? Just to make it practical. And I'm not saying nobody should ever eclipse that, but I just want to, it's like, it's for a lay audience, getting that in their head is going to be very, very difficult. So what, what kind of training activity does that look like? Sure, sure. So, um, this is going to vary across body types across, you know, with your cycling on a road bike versus if you're running, you know, miles. So this is going to be specific to you, but to put some kind of cartoon numbers on it, just to kind of ballpark that we're talking about here. Um, a typical adult males, uh, basal metabolic rate, let's say it's about 1800 calories a day.

Okay. So what's two and a half times that is, uh, 36 is about 4,500 calories a day. So if I have that right. So that's, that's the ceiling that you could burn pretty sustainably. Let's say as a kind of a ballpark, 4,500 calories a day. Well, if you already burn at 1800 calories a day at just to rest, you know, just as your baseline, plus, you know, if you are eating 4,500 calories a day to stay in energy balance, you're going to be burning 450 of those calories just on digestion, right? So now we're at, Oh, 2200 calories a day as, as just minimal survival stuff. Now you need to, uh, you know, you need to wake up in the morning, get out of bed, go, you know, it's walk around, have your normal sort of daily life. You don't just jump out of bed and run. Right. So there's other, there's other baseline stuff. Let's say you've got about 2000 calories in that scenario ish to play with. And that's a lot of training, right? I mean, a mile of running is something like a hundred calories and they're like, let me be just more. That's what I was. That's I just got my calculator out. So I was, I was doing the math for you. Yeah. So you can still, that's still a pretty high volume. Um, and you know, what I think what actually is that that's missing is that I think that extra energy just to kind of walk around and have a daily, your daily life is probably too low. Uh, probably imagine that remember that a typical guy in the U S burns 3000

calories a day doing almost nothing. Right. So maybe, maybe the limit on, on your, on your exercise volume above that is more like 1500 calories a day. Um, but that's a lot of volume. It's still a lot of volume, but a lot of it to, to kind of put a number on it and I'm going to, I'm going to back of the napkin in a little bit. It's anywhere between 40 and about 55 kilometers of flat level running for a normal adult size male. And when, when people, when people hear that they are going to know people who train more than that on a daily basis. And this is where it becomes quite interesting because it, because it gets to the sustainability aspect of it. Right.

What is enabling those people that we know have super high training volumes because they're there, those stories are out there. I trained 200 miles a week. I trained 300 kilometers a week, kind of every week for, you know, a decade. What could be enabling those people to actually do that? And they would be your best research subjects right there. Because in theory, at least if you were to run simple math on it, they're eclipsing that ceiling. Yeah. So I'll give you the physiology answer. Then Drew will give you the more informed ultra marathon or answer. Uh, the physiology answer is that they really aren't breaking the ceiling. And yeah, so I work in a lot of my work kind of bleeds over into the obesity field, right? You can imagine a lot of the work we do with metabolism and energy. A lot of this has, is relevant there.

We do a lot of studies that are in that space. And what you learn is that people aren't very good at keeping track of what they do every day. Yeah, that's true. Right. So, you know, they don't keep, they can't keep track of what they eat. They can't keep track of what they do and not through any sort of malicious fault of their own. They just, people just bad at it. I'm sure I'm bad at it too. I'm sure we're all typical. Right. Um, and so I would, my first, my knee-jerk reaction to what you just said is they're not really doing the training point because they can't, because they can't, or they're doing it, you know, six months of the year, but they're kind of conveniently forgetting the fact that, Oh, for the other four or five months, it wasn't really that high. They couldn't do that. You know what I mean? For whatever reason, Oh, well I had that week. I couldn't do this or that. Sure. Well, exactly. Um, anyway, that's, that's my cynical physiology answer and Drew might have a better, uh, real answer. I am far less cynical, although I think something you just said makes sense. Uh, I mean, it is possible that, you know, maybe they're going into serious debt, burning fat and muscle stores for a month or two at a time. And then they're repaying that debt by reducing training volume later so that, you know, over say a year metabolic scope isn't much over 2.5 or so.

Um, but I anecdotally believe that there are people that train this much and this is who I want to target for the next round of data collections. And I'm not sure I even want to limit it to ultra runners. I mean, um, some of the shorter distance runners, cyclists, a couple of mountain bikers I know are putting in massive volume. So Jason's question, you know, this is really the question that I'm already taking from this. What is enabling some people to perform at a higher level in terms of volume in terms of training volume? Um, are they actually adhering to this limit? Is the limit for them higher or are they doing more with less? Right. So I think there's really three possible answers. Well, there's four possible answers. One is Hermann's, which is that actually people are not training this much, that if you pan out far enough, you're seeing where they're repaying those, those deaths. Right. Um, I, I think people, some people are doing that. Um, and even if they're just total freaks, what is freaky about them? Right. So number one, one thing that could explain how some people are doing more with less or less with more, maybe there's a lot of variation in the economy of movement, you know, but I mean, running economy, well, that can vary what, like 30%, but that's mostly about running, running faster at a given oxygen consumption, right? Not necessarily running farther, you know? So I don't think, I don't think that variation explains it. Maybe there's a very, one thing we haven't mentioned, Hermann's work suggests that the ultimate limit, you know,

that actually sets the metabolic ceiling is your ability to digest and assimilate calories that it's really, you know, how, how good are your intestines at absorbing macronutrients and how good is your, you know, liver and muscles at, at packing and glycogen? How good are you at storing, you know, subcutaneous fat that's actually, you know, accessible during, during activity. So digestion and assimilation. So if that's the limit, maybe there's a lot of variation between people in how many calories they can absorb. And, you know, off the back of my, off the top of my head, I can think of some gross ways of potentially measuring this. I mean, you know, uh, is there a way to measure basically energy extraction from food? I mean, can you, I don't know, can you put a feces and like a calorimeter or something and measure how much energy is left in the stool, right? I don't want to do that research. If I ever have a lab with graduate students, maybe that would be, maybe that would be something they would do. I already deal with sweat and pee. I'm not dealing with poop too. Um, so that maybe there's a lot of variation in, in this capacity of digestion, maybe, you know, uh, I love to keep quoting the Anne Tracen quote, right? Ultra running is an eating event with some running thrown in, right? Uh, maybe it really is all other things being equal. If you've handled, you know, your blisters, if you've developed your aerobic capacity, if you know, you have good maximal fat oxidation, whatever the things are, uh, if you're able to really butt up against that limit, the metabolic limit, maybe the difference is,

you know, runner a can digest and assimilate more calories than runner B. So maybe that's it. And I think the third possibility is that there's variation in metabolic compensation. And this is an exciting direction that I can see, I can see us going in. I mean, um, maybe there is a real metabolic ceiling, which we are seeing. And maybe the reason that some can, can do more with less is they're able to pull back more calories from other expenditures with or without side effects. I mean, maybe the people who can run 150 miles a week are those who are able to really suppress, you know, reproductive investment in terms of sex hormones. Um, they're really suppressing, I don't know, immune function. You'd think there'd be side effects to all that stuff, but maybe there are people out there who can metabolically compensate, um, way better than others and maintain, you know, healthy physiology while they do it.

And I don't think we've tested any of those things. I mean, Herman's work looking at metabolic compensation is really recent. What last like five or 10 years. So a lot of questions still to look at there, but Jason, your point, how are some people doing so much and are they breaking through that, that ceiling? That's the biggest question. And I just want to add, Jason, can I mention your data or no? Yeah, no, yeah, please do. Okay. In our small sample size, I'm just looking now, you have the highest sustained metabolic scope of 2.6. So just over the edge. Yeah. Maybe I was just over training for a whole year. Was that the, is that the whole year? I mean, this is May, 2021 through April, 2022, based on the training records that you provided me, you're burning on average, 4,900 calories a day for 365 days. Uh, your metabolic scope is 2.6. Um, your training volume was pretty big, but not the biggest, the guy with the biggest training volume here, he ran four and a half thousand miles in that year or something like that had the second lowest metabolic scope.

So there's something happening here. There's some variation here that needs to be explained. And when it is, it'll have applications to, you know, Herman's ideas about the evolution of human metabolism and what constrains it, but also ultra runners. I mean, in a couple of years, I think we'll be able to hopefully actually have some insight into what is this variation? Um, how can you tweak it? How can you train to it? Maybe, maybe I'm getting a little ahead of myself, but. Well, once again, I mean, if I think about it from a training intervention standpoint, I look, I look at this research through a really broad and long lens that tells me that there is an upper limit to how much training volume somebody can sustain over the course of one or two or four years. And I just, I happen to be very privileged that most of the athletes that I work with, I have relationships with for many, many, many years. And having that scope, having a metabolic scope, if they've only got so much budget that they can work with over those long timeframes, yes, you can spend a little bit more than you're taking in for certain amounts of time, but you have to repay that in some organized fashion and training architecture. And in, in, in, in my observation and in my philosophy, training architecture should revolve around part or should partially revolve around that cornerstone of how

much energy that you, you want to expend to maximize the adaptation for certain periods of time. And then when those periods of time aren't as important, you can come back and you can repay that debt, so to speak. So this is why this is kind of like fascinating to me. And yes, it's a little bit esoteric right now. I was trying to pin some numbers down and it's still, you know, very, very, very fuzzy. But to me, it's extremely enlightening because it comes back to this overall philosophy of, yes, you can, yes, you can, you know, you know, burn it at two ends, but you're going to have to repay it at some point. And when you broaden the lens out far enough, you can see those undulations and people's training and how to make it the most effective possible. Yeah. Yeah.

Is there, I think that's a great way to leave it. Is there anything else that you guys want to leave the listeners with? Can they participate in the studies or any pieces of, of advice on how to look, how to look at this in order to inform their own training? I'll jump in right now. We're doing a study in sort of parallel to the one that Drew's leading. My lab is working on what these energy limits look like in women. So women athletes who are putting in high training volumes, we're focused specifically on runners because that's a well-known mechanically and energetically understood exercise. So if you're a female athlete, you are putting in lots of training through a pregnancy, right? We're focused on the pregnancy aspect of this. And you're planning on, we're not asking anybody to do anything that they're not already planning to do, but if you're going, if you're planning to maintain a high level of running through pregnancy, then let us know because we are recruiting for that study right now.

We've already had about 10 athletes through who've had successful pregnancies and we've measured their energy expenditures through, you know, all three trimesters. And it's, to watch that data come in is exciting and I'm not going to, I can't spoil it now. I don't know, we don't know, have enough to say anything yet, but it's been going really well. And it's another way to kind of test this limit. And it has obvious implications too, for, you know, half of the world out there who's, you know, needs to be active and wants to stay active potentially through a pregnancy that we, it's an area we don't know much about in reproductive health is, you know, if you're a high volume athlete going through pregnancy, how do you manage that? What does that do to your body? So it's got theoretical applications, the kind of stuff we're curious about. It's got, I think, really real world health applications to women who are, you know, women athletes working about pregnancy. So if you are, if that's you, send me an email and we'll get you involved in that study.

And if you are just, you know, a typical ultramarathon runner who isn't going to go through pregnancy like that, you know, get ahold of Drew and yeah, we'll recruit right now. I'll leave that link in the show notes for anybody who's interested. Drew, do you want to tack onto that at all? I mean, the only thing I would tack on and Herman and I haven't explicitly discussed it, but I would like to look, you know, with the remaining funding we have for this coming summer, maybe five more people, I want to find really high volume athletes. So I think I've already, I ran with him yesterday. I think I've maybe pegged down one of my buddies. So that would, that would be four. If you're doing like well over a hundred miles a week, pretty consistently, if you're a cyclist and you're putting in, you know, 20 plus hours a week, you are the people that I want to see now. I don't care how fast you are. It might even be great if we had a spectrum of faster and slower performers, but if you're putting in really huge volume, I want to see why I want to see if you're able to bust through that ceiling. And if not, why not? So be in touch.

And I'll leave that link to the, in the, in the show, in the show notes as well, you're going to have some people that listen to this podcast that are running over a hundred miles a week that are, that are going to want to test it. Because if we know anything about ultra marathoners and ultra endurance athletes, they want to, they want to see, and they want to know if they are the anomaly. If, if for no other reason, just to be the anomaly is part of the attraction of the sport. People always, you know, since that paper in 2019 came out where we sort of proposed this metabolic ceiling, um, I've had so many people reach out and either they want to be, they want to test to see if they can break through the stadium, which is awesome. Let's do that. Or people say, aren't you going to be so disappointed? You know, how are you going to feel when somebody breaks your pretty little hypothesis, you know? And, uh, I'm like, man, you don't get it. That would make me so happy. That would be awesome. Uh, so please come destroy this beautiful idea because that's how science moves forward.

Challenge accepted and gauntlet throw down. I hope that you guys get, uh, any number of inquiries from this podcast. Thank you guys for being on. I really appreciate it. Like, like I said, to the listeners, everybody out there right now, give these two a follow. Uh, if you are interested in the research that they're doing, hit it up in the show notes. Those of you on the YouTube version, go see Herman's book burn. It's a fascinating book. It's very intriguing and we'll definitely get your, uh, uh, definitely get you thinking. I'll leave a link to, uh, Herman's book in the show notes as well. Thank you guys for coming on the podcast. I appreciate it a lot. Thank you. Thank you, Jason. Thank you. All right, folks. There you have it. There you go. Much thanks to Herman and Andrew for coming on the podcast today. And more importantly, for the research and the work that you do in the field, and especially challenging some of our notions about human metabolism and how we got to where we got.

I certainly have thought a lot differently about this subject since first encountering Herman's work. And I've come to appreciate how difficult some of this research actually is to conduct by being a subject in Andrew's research project that we discussed during the podcast. So thank you to the both, both of you. If you want to get involved in either of their works or just learn a little bit more about them, there are a ton of links in the show notes. Y'all go and please check those out. Thank you to each and every one of you that are listening to this podcast. As always, this podcast is coming to you unsponsored. I don't have anything to show you. I'm not going to sell you any affiliate codes or athletic greens or aura rings or whoop straps for 20% off or anything like that. And I don't do that in order to make the content within this podcast as unadulterated and unfiltered as possible, because I believe that serves you the end user the best. If I do not have those restraints so you can help this podcast out tremendously simply by sharing it with your friends and your training partners and helping to get the word out about all of the incredible content that this podcast brings to you week in and week out. That is it for today, folks.

As always, we will see you out on the trails. Bye.