Episode 71 - Dr. Eric Trexler Uncovers the Dynamic World of Energy Expenditure

Discover the intricate dance of energy expenditure as we unravel the myths with Dr. Eric Trexler, an authority in this field. Our conversation breaks down the complex interaction between physical activity and calorie burn, guiding you through the additive and constrained models of total daily energy expenditure. With Dr. Trexler's insights, we shed light on Herman Ponzer's eye-opening research with the Hadza tribe, which turns the tables on our understanding of energy usage in sedentary Western societies compared to their highly active counterparts.

Timeline:

00:20 – Dr. Trexler explains in simple terms the additive vs. constrained model of total daily energy expenditure (TDEE).

4:38 - Hadza tribes (modern-day Tanzania); Dr Trexler joined Herman Ponzer’s lab in 2023.  

7:00 – Some do up to 35,000 steps per day.  How much movement is that?

10:00 - Once you reach a certain amount of total physical activity, there appear to be compensatory adjustments vis a vis TDEE. 

12:24 - Maximal measured EE per day over months seems to be around a functional limit of 2.5 x a person’s basal metabolic rate.  It scales to body size in general. 

15:00 – For pregnant women in the 2nd or 3rd trimester we may see a 2.2 range of metabolic scope

17:00 – Metabolic scope values as high as 10 in the short run.

28:00 – Metabolic adaptation

31:14 – Additive vs. constrained models

36:40 – Our energy intake is driven by the hedonic value of a given meal, not necessarily related to the energy needs of the person.

39:59 – Quality of exercise is best served by choosing better foods; exercise is a behavior that affects so many other behaviors.

47:37 – Are there tissue-specific changes in energy expenditure with age?  Does this explain, in part, the drop in RMR after age 60?

48:00 – Liver, Brain, Heart and Kidneys are much more metabolically active than skeletal muscle – do these organs decrease in EE?

 

About our special guest:  Eric Trexler PhD 

Dr. Eric Trexler is a postdoctoral researcher in the Department of Evolutionary Anthropology of Duke University, where he conducts research on cardiometabolic health and energy expenditure regulation. He has a PhD in Human Movement Science from UNC Chapel Hill and has published dozens of peer-reviewed research papers related to exercise, nutrition, and metabolism.

About the Show

We cover all things related to sports science, nutrition, and performance. The Sports Science Dudes represent the opinions of the hosts and guests and are not the official opinions of the International Society of Sports Nutrition (ISSN), the Society for Sports Neuroscience, or Nova Southeastern University. The advice provided on this show should not be construed as medical advice and is purely an educational forum.

Hosted by Jose Antonio PhD

Dr. Antonio is the co-founder and CEO of the International Society of Sports Nutrition and the co-founder of the Society for Sports Neuroscience, www.issn.net. Dr. Antonio has over 120 peer-reviewed publications and 16 books. He is a Professor at Nova Southeastern University, Davie, Florida in the Department of Health and Human Performance.

X: @JoseAntonioPhD

Instagram: the_issn and supphd

Co-host Anthony Ricci EdD

Dr Ricci is an expert on Fight Sports and is currently an Assistant Professor at Nova Southeastern University in Davie Florida in the Department of Health and Human Performance.

Instagram: sportpsy_sci_doc and fightshape_ricci

Transcript

Speaker 1: 0:04

You've been mentioning and I want, for the benefit of the audience. You've used the terms constrained and the additive theory of total daily energy expenditure. Could you, in just very simple terms, tell the audience additive versus constrained?

Speaker 2: 0:19

Absolutely. Yeah, additive is that beautiful story we tell ourselves. That makes perfect sense, right? So the additive model basically says if I decided every day I'm going to do more exercise and I get out my ACSM book, I do the calculations and it says this should cost a hundred calories a day, the additive model says my total daily energy expenditure should go up by 100 calories a day because I just added 100 calories of exercise, right? So in a perfect world that would be true. We go to bed and we never worry about it again.

Speaker 2: 0:54

The constrained model suggests that when you are super sedentary and you are in neutral even positive energy balance and you add a little bit of exercise to your day, that's still true and I wouldn't argue that. However, when we start getting to much higher volumes of exercise where you know, say you're an elite athlete who's already putting in high volume and you're going to add an extra 200 calories worth of training to your daily routine, and let's say, maybe because you're doing so much exercise, you're actually under fueling and maybe you're in a small energy deficit what we find, you know, the additive model would say you're still going to have an increase of I think I said 200 calories a day from adding those 200 calories of exercise? The constrained model would say probably not. You know, your total daily energy expenditure may only go up by maybe half of that. And you might be wondering why we would bother putting together.

Speaker 2: 1:52

Not me, I didn't invent the model, but why would someone bother to put such a model together? And the reason is because we have seen enough of these particular instances where the additive model just doesn't seem to work, and weight loss trials are actually a good example of that. So if you look at a trial that says all we want to do here is add exercise to help people lose weight right, and the e-mechanic trial is one of those trials what you find is that people lose a fraction of the weight that you would calculate and their total daily energy expenditure only goes up by a fraction of what you would predict.

Speaker 1: 2:27

Welcome to the Sports Science Dudes. I am your host, dr Jose Antonio, with my co-host, dr Tony Ricci. You can find us on Spotify, apple Podcasts, rumble and YouTube. Our guest today is Dr Eric Trexler. He is a postdoc in the Department of Evolutionary Anthropology at Duke, where he conducts research on cardiometabolic health and energy expenditure regulation. He got his PhD in human movement science from University of North Carolina at Chapel Hill. He's published dozens of peer-reviewed papers related to exercise, nutrition and metabolism, and the reason.

Speaker 1: 3:02

I wanted you on here is because it really deals with one of the pressing questions in the world of exercise, although it seems that the people who are pushing this I believe Herman Ponser correct me if I'm wrong he's actually coming from an evolutionary biology perspective, not technically exercise science, correct, yeah, yeah, so I think this is. To me, this is one of the more fascinating topics in our field because it goes to the heart of okay well, tony and I we're a bit older than you. We do recall, you know, 1970s, there were very few obese Americans. It was, and in fact I remember in grade school there was always the one fat kid and then everyone else was normal, normal weight. Now it's the normal weight people are the ones who are the rarity, and now you have this abundance of overweight and obese kids.

Speaker 1: 3:58

So it's not like we've evolved to be different humans in like 30 or 40 years. So something weird is going on. So let's start with this. Let's go back to some of the work that Herman did with the Hadza hunter-gatherer tribes in what is now modern-day Tanzania and explain the data he came up with and why it was so surprising to really all of us in terms of wait a minute, so us sort of sedentary Westerners expend as much total daily energy as these people who seem to walk all day. Explain a little bit about that, because I think we need a lot of background.

Speaker 2: 4:38

Yeah, yeah, so to be clear, I joined Herman's Lab in 2023, which is kind of long after a lot of the original Hadza data were published. So I want to be clear that I wasn't, like you know, in the field with them or kind of involved in those original studies. But obviously, being in the lab, we're continuously building upon our prior work, testing new hypotheses that branch out from prior work, building upon our prior work, testing new hypotheses that branch out from prior work. So I am familiar with some of this kind of original data that have kind of brought us where we are now as a lab. So, yeah, I think you know we are in the Department of Evolutionary Anthropology over here at Duke and you know we part of the research we do is looking at a variety of what we would call rural populations and in the global context, that includes really a wide range of different populations and economic kind of structures within those populations, right? So we had a big workshop a couple months ago where we brought in colleagues and collaborators from all over the country who study rural populations in the global sense.

Speaker 2: 5:49

Now, some of us do study the rural United States, right? So basically, the census determines if a county is rural or not. So some folks study rural Americans but other folks study, you know, different populations that perhaps have an economy that's more like a hunter-gatherer type of economy, pastoralists who kind of tend their herds and maybe do some very small-scale farming. But there's really a diversity of kind of economic structures in these populations and in some of them there is a little bit of market integration where you can actually go to a store to purchase food.

Speaker 2: 6:28

But in many of them, talking to our colleagues, you know, like you were saying, to get a drink of water is no small task. You know it involves a daily going a fairly far distance to gather water for the day and bring it back. So, um, you know these, these are definitely populations where it's not unusual to see, uh, average step counts that are, you know, in America it's like you shoot for 10,000 a day and you're like pushing it, like can I get there? Um, it's not unusual to see average step counts in these different populations in the, you know, 20,000 a day range. It's not unusual at all and some individuals you'll see up around 35,000 steps a day.

Speaker 1: 7:09

Right, you put that in terms of minutes or hours. What would that be like? 20,000 steps?

Speaker 2: 7:14

Hmm, you know, I actually don't know the easy conversion off the top of my head in terms of time, but needless. So here's my best analogy when I was doing my dissertation, research, my study, I had to like run my blood samples back and forth and I would do these 16 hour data collection days. Each participant took four hours. I do like four or five a day, sometimes stagger them. I was running around like crazy all day, I mean, and never stopped, always moving. You know, usually on a clock I got to get back to the other lab, I got 90 seconds and those were the days where I hit like 25 to 28,000 steps a day. So I mean it is a lot.

Speaker 1: 7:55

You're doing work.

Speaker 2: 7:56

Oh, yeah, yeah, yeah, big time. So, yeah, I mean, we're talking about average values that are often, you know, three, four, five times what we see in the typical American in terms of step counts. So, anyway, I think the really interesting paper that kind of caught my eye out of Herman's lab was in 2016, where they kind of gathered and aggregated data from several different populations and combined it all to kind of it's kind of like the definitive paper that people point to when they talk about the constrained total energy expenditure model, and the idea is not necessarily that physical activity is unrelated to energy expenditure. I think most folks who study this topic and are familiar with it will acknowledge when you go from very inactive to moderately active, we do expect that your total energy expenditure will go up to some extent. But what's really interesting in this 2016 paper is they took data from, I think, five different populations with very different activity levels in terms of step counts or accelerometry metrics, and they plotted out in deciles total energy expenditure per day, adjusted for body composition, and they're using doubly labeled water, which is a fantastic method for daily energy expenditure in free living individuals, and what you see at the bottom portion of that distribution is what you'd expect.

Speaker 2: 9:26

More active people burn more calories per day, but what's really interesting is that when you get to the top level, the top half of that spectrum, things start to really flatten out. So it's not this perfectly linear additive relationship where every time you increase your activity level by X percent, you increase your total energy expenditure by Y percent. We find instead more of a curvilinear relationship where there's a bit of a plateau at higher energy expenditures and the working theory is that there is some constraint, not on the low end, but on the high end, where, once you reach a certain amount of total physical activity, perhaps there are, or there appear to be, some compensatory adjustments in some less essential elements of energy expenditure that work to keep your total energy expenditure within a particular range. Now, it's not foolproof, and what we're really looking at with the total energy expenditure model is the maximum sustainable energy expenditure over time, in long time courses, right? Because, jose, if I told you, hey, I'm going to give you a million dollars if you burn 7,000 calories tomorrow, you'll do it, you'll get on your paddleboard and you'll be happy as a clam paddling away.

Speaker 2: 10:47

I've seen your Instagram, right?

Speaker 1: 10:50

I'd be on that board all day.

Speaker 2: 10:51

Exactly. But you could do it right. You could do it and we have ample data from ultra marathoners right and say, yeah, if you really need to burn 9,000 calories today, you could do it. It's going to be not a fun day but it can be done.

Speaker 2: 11:07

But what's really interesting is that there is a steep drop off. If you look at the curve of kind of maximal measured energy expenditures on the Y axis, you know in calories per day, and then on the X axis you have the duration of the activity right, so it could be a single day event or maybe like a three day event or a two week, you know, like really prolonged staged race, there's this immense drop off in what we see as the maximal observed energy expenditure per day and when you start to extrapolate that out over months, what we start to see is what appears to be a functional limit and I can only speak for myself, but I know folks in our lab when we discuss it we don't necessarily speak of it yet as a true physiological limit, as if it's like a law of nature. But what we often acknowledge is that we haven't really found anyone where we see their energy expenditures above this curve when we kind of fit energy expenditure per day to the duration of activity and what we seem to find as a kind of prolonged, sustainable daily energy expenditure. The kind of ceiling that we've observed so far tends to be about 2.5 times an individual's basal metabolic rate. So it scales to body size, generally speaking, um and so you know, uh, we do these BMR units because it it kind of just works with the modeling.

Speaker 2: 12:40

But you know so if you're, if your BMR is 1500 calories per day, then you know two times that you're talking about. You know 3000, right, three times that you're talking, 4500. So we start to, when we look at two and a half times BMR, we start to see numbers for the maximum sustainable amount that actually do look pretty similar to what we see in doubly labeled water studies. When we look at, maybe, soccer players or basketball players or rugby players, we see those elevated expenditures. Right, it's not like the model suggests that a totally sedentary person and an Olympic soccer player have the same total daily energy expenditure, but the model argues that there's a constraint that seems to be observed when we try to sustain really high energy expenditures over time.

Speaker 1: 13:29

So I want to bring sort of a sports application here, so the Tour de France, where these cyclists are expending a lot of energy daily, but also consecutive days and, uh, I mean, aside from the use of performance enhancing drugs that sort of helped them get through the event. Um, explain how that would work in that population, cause they're, they're, they're the population of athletes, I think of where, holy shit, they're really burning a lot of calories every day.

Speaker 2: 14:01

Oh, yeah, yeah, so I'm actually looking. I think the best paper for this that kind of demonstrates this really steep drop off when we look at energy expenditure versus time there's a paper by Thurber and colleagues in 2019. I know Herman was a contributor to that paper. But when we talk about these BMR units, we call that metabolic scope. So, like I said, in the really long term, we see that it appears that a kind of natural limit seems to be about 2.5-ish times basal metabolic rate and I should acknowledge our lab.

Speaker 2: 14:37

It's not that we are working tirelessly to defend that as a limit.

Speaker 2: 14:42

We are trying to break it, and so we currently have research going on with pregnant women who are doing high volume running throughout the duration of their pregnancy, because what you find is a lot of pregnant women without any structured exercise. Just from the energy cost of growing a baby, especially like second and third trimester the energy cost of growing a baby, especially like second and third trimester we often see metabolic scope getting up into the like 2.2 range, and so it's not hard to imagine, okay, well, if we push a decent running volume on top of that, we should be able to break right through 2.5 and get up near 3.2 maybe. So we're trying to disprove it and so time will tell. That data collection's ongoing and should be presentable within the next six to 12 months, I would think. But anyway, I know Herman has done some research specifically on Tour de France energy expenditure values. But do you happen to know how long the Tour de France is in days, roughly, I'm not super familiar with I think it's about 28 days.

Speaker 1: 15:49

Tony, are you familiar?

Speaker 3: 15:51

I think it's a little shy of that, but not much.

Speaker 2: 15:57

Yeah, yeah, run that number by me again. What was that?

Speaker 1: 16:00

I think it's about 28 days.

Speaker 2: 16:02

Okay, okay, yeah. So 28 days, just eyeballing this curve, that that's near the like fairly vertical part of the curve. So in terms of metabolic scope values. So, for example, in single day events, it's not um unheard of to see values of like.

Speaker 1: 16:20

Eric, let me correct that. It's a 21, 21 day long stages over a 24 day period, about 3,500 kilometers total.

Speaker 2: 16:29

So yeah, yeah, so, um, I know that Herman's published data with tour de France athletes, um, but I don't have any numbers to dazzle you with off the top of my head. But I will say, um, in the paper by Thurber and colleagues, I think they have Tour de France data within this, but I'd have to double check that. I know they have cyclists, but they have cyclists Arctic trekking race across the USA, which is like daily marathons, and then individuals who are pregnant and lactating and what they find is, when you're talking about things in the shorter timeframe, it's not at all unusual to see metabolic scope values above 10, right, and we're talking about the long-term sustainable limit being around two and a half. Give or take the theory, as much as they show us an instance of energy expenditures that are possible in the short term but very unlikely to be sustained in the long term. Not that you would want to, right, I mean, like no one is, and I think that's what really interests me is I'd love to figure out more about.

Speaker 2: 17:40

You know, there are different theories about why this kind of purported metabolic ceiling exists. One of the theories is that there is a certain limit to the amount of uh nutritional energy that we can extract from our gut in a given day. Um, you know that that eventually it's just difficult to really extract that many calories efficiently. To really extract that many calories efficiently, um, and that basically, uh, if, if alimentary extraction maxes out at about, at about 2.5 times metabolic rate on average, then if you're trying to do more than that, like I said, for a certain period of time you can, but you will necessarily be in an energy deficit and the magnitude of that deficit will be scaled to how crazy you're going above that limit, right, and so the more you push it, the larger the deficit. That puts you in a position where not only are you doing a ton of exercise that's tremendously difficult to recover from, but now you're almost by default in a large caloric deficit when you're trying to recover from it, which is going to make your recovery even worse. When you're trying to recover from it, which is going to make your recovery even worse. And the more you're doing, the more you have to recover from the fewer resources you really have available from a nutritional perspective to recover from it.

Speaker 2: 18:53

And so part of me wonders to what extent is this relationship between maximal sustainable energy expenditure and time? To what extent is that physiological? And to what extent is it physiological and to what extent is it essentially a practical reality that if you try to maintain an untenable energy expenditure via exercise, that is putting you into a tremendous energy deficit, at what point is your body just going to break down? And you know, if you think of an endurance athlete who says, yeah, I'm going to run daily marathons and I'm going to try to do it for months on end and every day I'm going to be in a 2000 calorie deficit, I don't think any of us think they're really going to get, you know, very far doing that without some type of injury occurring or some other type of medical. You know roadblock to that goal, yeah, so I'm sorry that this is fascinating.

Speaker 3: 19:45

So to your point, and we would make an assertion on this do you think that, let's say, the 2.5 could be if there were ways to ingest more calories during those long training durations which actually limit the potential to do so? Maybe via liquid? Maybe ways to bring in carbohydrate through? You know other than hard foods to bring in carbohydrate through. You know other than hard foods? Might that impact it? Do you think, like, if we can get in an extra 1000 calories per day, let's say from what the previous high end point was? So you're essentially saying it's not even related to energy availability, because there's going to be a cap. But do you think if we could increase energy availability, that too might push us a little higher than the two five you know, because obviously we can't take, if you're training 10 hours a day, you're just limiting how much food you can consume as well, right?

Speaker 2: 20:36

Yeah, now I think, um, the, the purported ceiling and I'm going to keep saying purported because we don't have enough evidence yet yet to call it, you know, a true hard ceiling but that is based on the data so far. That suggests that the limit of kind of extraction from the gut, including food and beverage, usually tends to be about in the ballpark of 2.5 times basal metabolic rate. However, to your point, I would be really intrigued to see well-controlled study designs that use uh routes of caloric administration that you know like um. So if you're like hanging an IV and providing nutrition uh from from that type of um, uh type of route, I would be curious to see if there are other ways to kind of facilitate nutritional interventions and and maybe push beyond that Um, I, I'm a lowly bodybuilder turned researcher.

Speaker 2: 21:34

I don't know enough about uh. You know really creative forms of nutritional provision, um, but uh. But it would be something that uh, I think if you could. You know and, to be fair, you know, when we look at you know finding better ways to facilitate nutrient extraction. You know, maybe there are other ways, even with food that we could talk about, like a low residue diet with kind of minimal fiber and semi or non-digestible carbohydrate. Maybe we're being really meticulous about sources of protein and carbohydrate utilizing a combination of carbohydrate transporters in the gut. Who's to say that you can't really dig into the nuances there and get a touch above that and at the level of high-performance sport that could theoretically yield an advantage if you're able to do so. So that's where it comes into. You know you might wonder, well, why haven't you guys done that study yet? And that's where I would kind of tap the sign and say, hey, evolutionary anthropology.

Speaker 2: 22:42

So, going back to Jose's you know initial question, a lot of what got us here is these curiously low energy expenditure values in hunter-gatherer populations for ago, where they found that when you are providing plenty of fuel and you are not basically out exercising your limit of energy consumption, the additive model of energy expenditure actually does pretty well. So the more that you increase your activity, the more your energy expenditure goes up. But what they did was they separated their analysis into people who were in positive energy balance, neutral energy balance and negative energy balance, and what they found was that the constrained model really seems to shine and really seems to be much more appropriate when people are specifically in negative energy balance. And I think that's probably one of the most misunderstood elements of this model or theory is the fact that it really helps us better understand why most athletes are able to have much higher energy expenditures than your typical sedentary individual, which is because they're exercising plenty, but not 9,000 calories of expenditure a day on their normal training and they're able to replace those calories really effectively, and so we're seeing that they're not really in a tremendous energy deficit during those training periods.

Speaker 2: 24:20

I think something that helps me make more sense of these surprisingly low expenditure values in hunter-gatherer communities.

Speaker 2: 24:31

Where it's not unusual to see tremendously high step counts is when you consider the nutritional resources and the typical energy intake within that population.

Speaker 2: 24:41

You kind of see this interplay between activity, energy expenditure and the, the way that calories are going up or down in relation to that activity, and so if you're in an environment with limited nutritional resources you're in a much more likely scenario that the constraint model will apply as activity levels get higher.

Speaker 2: 25:03

It's almost like, if you know, if we were working with cross country athletes but we told them, instead of eating your normal 3600 calories per day, we're going to go ahead and hold you to 2000. I think you would see that, where the additive model used to work out pretty well, now we're looking at something where a constrained model seems a lot more appropriate. So I do think that the interplay between activity level and energy balance energy availability, nutritional resources. In that specific you know the like ugly looking proof PDF just went up a few days ago, but it's from the e-mechanic trial that they did down at the Pennington Biomedical Research Center and it's really fascinating because it's really opening my eyes and kind of helping me helping me better, I think, better understand the relationship between exercise, energy compensation or the constrained energy expenditure model, and one of my hobby horses from back in the day, which is metabolic adaptation, and so the first thing I ever published was in the ISSN journal about metabolic adaptation.

Speaker 2: 26:26

It was a review paper back in 2014. And we were looking just at from a dietary perspective, you know, in people who exercise. But we were looking at, you know, for people who are really restricting their diet and trying to train hard. What are these? You know, kind of broad adaptations and energy expenditure that start at the hypothalamus, largely dictated by the hormone leptin, and then the hypothalamus integrates this leptin signal and has all these downstream effects on our energy expenditure and particularly the efficiency, the energy efficiency of our movement. Right, because when you look at where metabolic adaptation really makes an impact on energy expenditure, it's not necessarily resting metabolic rate, it's really non-exercise activity thermogenesis. And I've made the mistake over the years of getting too caught up in thinking that non-exercise activity thermogenesis is equivalent to non-exercise physical activity. Activity thermogenesis is equivalent to non-exercise physical activity and they're they're they're distinct. You know, non-exercise activity thermogenesis can go down, even if you're keeping up the same step count and the same same amount of mechanical work, if you're doing that work with more efficiency from an energetic perspective.

Speaker 2: 27:45

And there are there's a series of two incredible studies, uh, out of Columbia. Uh, it was Rosenbaum and Liebel. Um, who they? They did some of the I think some of the best work that's ever been done on metabolic adaptation. And what they did was they took people at their baseline weight and after a 10% weight reduction so a long effective weight loss trial. Um, they got these measurements at baseline and after 10% weight reduction so a long, effective weight loss trial.

Speaker 2: 28:09

They got these measurements at baseline and after 10% weight reduction and they were looking at the energy cost of exercise and they really went all out in terms of controlling everything. They even went so far as they used DEXA. They were measuring energy expenditure while cycling. They used DEXA to look at the weight of their legs and actually used little weights to replace the leg mass that was lost during the weight loss portion of the trial, because they really wanted to hone in on the mechanical efficiency with which they were doing work with their musculature.

Speaker 2: 28:46

So they have them redo the cycling protocol after the weight reduction and what they found was a pretty substantial increase in the energetic efficiency of muscular work, specifically at very low intensities. So we're talking about 10 watt cycling, 25 watt cycling so that's on the metabolic adaptation side of things. 25-watt cycling so that's on the metabolic adaptation side of things. This newest paper that I mentioned that was published a few days ago, when they were looking specifically at the folks in this e-mechanic trial who had the highest magnitude of exercise energy compensation, these compensatory mechanisms that essentially make the constrained energy expenditure model work and make it relevant. These folks didn't really have depressed resting metabolic rates, and so I am increasingly and this is me interpreting papers that just hit the presses, so I'm speaking only for myself here- but I mean yes, exactly.

Speaker 2: 29:46

So yeah, if I was wearing a Duke t-shirt, I'd take it off right now.

Speaker 2: 29:50

I'm not speaking for anyone but me, but I'm increasingly starting to think that exercise energy compensation probably has more in common with metabolic adaptation than we've previously assumed.

Speaker 2: 30:04

And I'm starting to think that when you look at how the energy deficit plays such a key role in some of these large magnitudes of exercise energy compensation, I'm thinking that after five, 10 more years of research, we're going to end up tracing this all back to the hypothalamus, and I wouldn't be shocked if leptin is ultimately kind of the key to both uh, to both sides of this coin here.

Speaker 2: 30:28

So all of that is to say, um, when you think, like we see these folks, these hunter, gatherer folks who are walking 20,000 steps a day and why is their energy expenditure not scaling linearly? I think a little clue that we can get from metabolic adaptation is that when you're doing low, low intensity activity, we've seen with metabolic adaptation is that when you're doing low, low intensity activity, we've seen with metabolic adaptation that the same steps cost fewer calories if some of these hypothalamic adaptations are in place to conserve energy. So there's a completely analogous adaptation with dietary restriction, and I'm trying to convince myself that it wouldn't apply to exercise, but I can't. Maybe I will someday, but for now I'm thinking that these two instances kind of map onto each other pretty well.

Speaker 1: 31:15

You've been mentioning and I want, for the benefit of the audience. You've used the terms constrained and the additive theory of total daily energy expenditure. Could you, in just very simple terms, tell the audience additive versus constrained?

Speaker 2: 31:30

Absolutely. Yeah, additive is that beautiful story we tell ourselves. That makes perfect sense, right? So the additive model basically says if I decided every day I'm going to do more exercise and I get out my ACSM book, I do the calculations and it says this should cost 100 calories a day, the additive model says my total daily energy expenditure should go up by 100 calories a day because I just added 100 calories of exercise, right? So in a perfect world that would be true. We go to bed and we never worry about it again.

Speaker 2: 32:04

The constrained model suggests that when you are super sedentary and you are in neutral even positive energy balance and you add a little bit of exercise to your day, that's still true and I wouldn't argue that. However, when we start getting to much higher volumes of exercise where you know, say, you're an elite athlete who's already putting in high volume and you're going to add an extra 200 calories worth of training to your daily routine, and let's say, maybe because you're doing so much exercise, you're actually under fueling and maybe you're in a small energy deficit what we find, you know, the additive model would say you're still going to have an increase of I think I said 200 calories a day from adding those 200 calories of exercise? The constrained model would say probably not. You know, your total daily energy expenditure may only go up by maybe half of that. And you might be wondering why we would bother putting together.

Speaker 2: 33:03

Not me, I didn't invent the model, but why would someone bother to put such a model together? And the reason is because we have seen enough of these particular instances where the additive model just doesn't seem to work, and weight loss trials are actually a good example of that. So if you look at a trial that says all we want to do here is add exercise to help people lose weight right, and the e-mechanic trial is one of those trials what you find is that people lose a fraction of the weight that you would calculate and their total daily energy expenditure only goes up by a fraction of what you would predict.

Speaker 1: 33:39

Yeah, no, this is fascinating because as exercise scientists and I'm familiar with that data where it's weight you get very minimal to moderate weight loss with just exercise.

Speaker 2: 33:51

Yeah.

Speaker 1: 33:51

However, you know we are, you know we like to recognize patterns, and the pattern I've seen in my life is that while people exercise a lot, maintain pretty good body composition throughout their life. So there's something going on with exercise and weight management and body composition, that there's something else there besides just energy expenditure, because people who are lean they work out a lot.

Speaker 2: 34:16

Yeah, oh, absolutely, and I would point to two things. First of all, a huge misconception is that when you go to the Ponser lab, everyone thinks you hate exercise and you think it's dumb. That's not true, okay, no, if you ask Kermit what is the single best thing you could do for your health, exercise is at the top of the list, right? Yeah, so there are tremendous health benefits of exercise and, when it comes to body composition, obviously even cardio in certain populations, uh is going to actually contribute to better body composition, addition of lean mass and, uh, you know, an offset of fat mass, uh, at a given body weight, right? So there's the body composition element of exercise, where, where you are loading muscles and that certainly helps with retention of greater and accretion of fat free mass, and then add in resistance training and that's even better in terms of body composition. The other element that I think is lesser known is that there's a really fascinating review paper by someone with a French last name that I can't remember off the top of my head I'll have to look it up and send it to you. My head, I'll have to look it up and send it to you. But they are reviewing a small body of literature, but a really fascinating body of literature which shows it hints at an appetite regulating effect of physical activity.

Speaker 2: 35:39

And so what they argue in this model, with empirical data to back it up, is that there are basically competing regulation systems controlling how much we are inclined to consume. You know appetite regulation, and not just appetite but also desire to eat, which is technically a little bit different. So what they argue is that at very low levels of physical activity, in very, very sedentary people, our energy intake patterns are primarily regulated by hedonic factors. Right, so we don't eat. If we're super sedentary, we don't say it's time for dinner, because I burned 2,800 calories today and I've only consumed 1,600 so far. So I need to make up that difference. We eat dinner because it's dinner time and we are likely to gravitate towards something that tastes nice. And usually our energy intake is not being scaled to any kind of physiological titrated energy balance equation. It's being driven by the hedonic value of consuming another meal and some of those neurophysiological rewards that we uh, that we experience when we consume another meal. And usually what that does is, for the typical American, for example, put us in a slight energy surplus, and it doesn't have to be huge. If you maintain a 150 calorie surplus per day for 50 years, uh, eventually you've gained a considerable amount of weight.

Speaker 2: 37:07

Now, obviously, at a certain point you know there's other appetite regulatory factors that come into play as body fat changes and things like that. But you get the idea. So the idea is, when you're very, very sedentary, usually the hedonic system is kind of regulating your appetite and your food consumption habits. But as you start to increase and go to being moderately active or even highly active, that hedonic control system kind of fades into the background and the actual physiological system dictating, you know, the pressure to achieve neutral energy balance starts to really take over in terms of the key appetite regulating system or mechanism. So the idea is, when individuals go from being super sedentary to moderately active or highly active instead of eating because of hedonic drivers, there's a much more titrated appetite regulating response.

Speaker 2: 38:00

That kind of takes over, and so that could very well feed into what what you're referring to, which is the fact that people who maintain a high level activity throughout their lifespan I wouldn't question that they do tend to be considerably leaner, while the tricky thing is, on the other hand, when we tell someone who is 45 and they're enrolling in a study that's only open to people with a BMI over 30, and we say, hey, exercise five days a week and we'll see how much weight you lose. Am I over 30? And we say, hey, exercise five days a week and we'll see how much weight you lose. It's like a kilogram and a half after 24 weeks, right, and so it's difficult to hold both of those truths, uh, in each of your hands, but they're both reliably observed.

Speaker 1: 38:37

Yeah, and that's, you know, that's interesting, it's, uh, and I think part of the the reason those of us in the exercise science field and I actually include you in there, Eric- You're still an exercise scientist.

Speaker 1: 38:53

The idea that a lot of people, it seems that they go to the gym purely on I need to burn calories, because I'm eating calories, when in fact, as you mentioned, it affects other behaviors. It's not just calories in. Therefore, if I eat a donut, I need to be on that stair stepper for 30 minutes. I mean, what a shitty way to live. I couldn't imagine that. You know so, but. But I think what's really cool about this and I'll use layman's terms it sounds like I guess good behaviors tend to cluster, meaning, if I'm exercising six days a week, you know, one to one hour to 90 minutes a day, I need to make sure I'm eating the right food so that I can exercise the next day, versus, you know, I think I'll eat saltine crackers, maybe have a donut and there's a bag of Doritos and I'll watch TV, and then I feel like shit the next day. So maybe I don't know if humans sort of they they figure out this pattern, maybe when they're young. It's like holy shit. I should probably eat better because I need to recover.

Speaker 1: 39:52

But, that's my non-scientific explanation. It's like well, I need good behaviors to cluster to be better at exercising.

Speaker 2: 39:58

Yeah Well, and especially like if you're someone who actually values the quality of your exercise, if you're going to exercise because you either enjoy it or you're pursuing some performance oriented goal, you know it's not going to cut it to just say I need to hold onto the treadmill for dear life and survive for 40 minutes. Right, you want to go and actually perform the next day.

Speaker 2: 40:18

And like you're saying, I mean the number of behaviors that that impacts. You have to be fueling effectively, you have to be hydrating effectively. If you exercise more, there's ample evidence that you will tend to sleep better. So now you're actually impacting your sleep habits as well, and you have to get to bed because you got to work out in the morning and you better not be hung over for it, right, and you better not have a bunch of tar in your lungs.

Speaker 2: 40:40

So, like, yeah, the number of health promoting behaviors that compound just from having that single thing of I enjoy exercise and want to do it well, I mean it's it's incredible to see the branching effects of how that reaches into almost every, almost every adaptable health behavior that we can choose to engage with. You know, like, if we think about the things that we can really control you know your genetics you get what you get. But when we talk about all those other habits that we can actually modulate and manipulate to benefit our own health, if you wake up in the morning and try to exercise effectively that day, like you said, you're probably going to be having downstream effects on a lot of those different behaviors without even really caring about them. To be honest, in isolation.

Speaker 1: 41:28

Okay, I want to ask a fun question. Oh, Tony, do you have one Cause?

Speaker 3: 41:30

I have well you could. It backs us up a little bit. But and, joey, this could go to you, eric, because you're so good in skeletal muscle plasticity, so inherent in you know, obviously, this large training volumes, they have to be somewhat endurance based, right, You're active, and active Are there? Can there be immediate changes? And I know, eric, you referred to a 2A guy and over the course of two, three, four weeks at a time, there's immediate adaptation decrease in skeletal muscle size, maybe increase in mitochondrial number and both efficiency, increase in myoglobin. Could that possibly be one of the contributing factors that leads to that efficiency over that duration? Or is that too short of a window? I guess that's what I'm asking.

Speaker 2: 42:27

So in a practical sense I would say yes, but in a methodological sense, in terms of this body of research, I would say no, Okay. And the reason I say that is, you know, if you start work so like when we talk about energy efficiency over time with an athlete a great example is me swimming I can't swim. I failed out of swim lessons. They told me to stop coming. As a kid, they're like it's not going to happen, right? So if I try to swim across a pool, it's going to be ugly. I'm going to burn untold numbers of calories as I fight for my life, right, Eventually I will build up more efficiency. There will be, you know, just from improvements in my, my, you know, my, my motor patterns of swimming. Yeah, and if you go from a somewhat good runner to an elite runner, there will be greater mechanical efficiency there. So if we zoom out in the broadest sense, those types of things do contribute. And the same thing, that longer term training response of perhaps becoming enhancing your aerobic capacity, having less glycolytic reliance, that stuff will come into play in the broadest sense. But the reason I don't think it necessarily applies directly to the exercise energy compensation literature is because I told you.

Speaker 2: 43:37

Those Columbia studies on metabolic adaptation were incredible.

Speaker 2: 43:41

One of them, in addition to accounting for the loss of actual leg mass and accounting for that, they also accounted for the aerobic fitness level of participants.

Speaker 2: 43:52

They basically trained them just enough to ensure that they did not become more or less aerobically fit throughout the duration of that trial, and what they still found was that after a 10% weight reduction there was a shift in substrate utilization. And so what they think is and it's not that they improved their capacity for lipid metabolism with intramuscular, but it seems like there was a clear shift where they were less likely to do glycolytic metabolism for energy production after this loss of body weight and this metabolic adaptation occurred. So they argued that there was probably a hormonally mediated shift to prefer the utilization of lipid to conserve carbohydrate and utilizing lipid for ATP is just more economical in terms of generating that energy. So long-winded answer, but there does seem to be, within these kind of hypothalamic mediated kind of neuroendocrine adaptations, it does seem like there's a shift in substrate that is probably not directly related to changes in muscle morphology or aerobic training adaptations.

Speaker 3: 45:05

Great. Thank you, that's fascinating Wow.

Speaker 2: 45:07

I can't believe I had an answer for that. It was a good one.

Speaker 1: 45:11

No, this is a, this is one is uh um, it's relevant to us old guys Um, it was a paper by Zampino at all, looking at longitudinal changes in resting metabolic rate, and I remember when this paper came out, people in the exercise and fitness community would say we're saying see, I told you, your resting metabolic rate doesn't change, doesn't start to drop off until and I'm looking at the figure now it looks like age 60, it's pretty flat ish, and then by age 60, it starts to drop. So so, tony, Not happening.

Speaker 3: 45:48

Better than ever.

Speaker 1: 45:48

Joey, I hope you're right. I hope you're right. So my question is why? What is it about age 60 versus age 40 or 50? Because, anecdotally, you know, I remember when I was in college a long time ago.

Speaker 2: 46:03

It's like, oh yeah, when you hit age 30, or metabolism suck, and definitely at age doubly labeled water database that's maintained by the International Agency for Atomic Energy, and so they had all this doubly labeled water data from individuals who are literally weeks old, all the way up to people in their, I think, late 90s. So they looked at total expenditure over the lifespan and they also found that total energy expenditure right around 60-ish is where it starts to tail off a little bit. And I think I know in that paper they speculate about the mechanisms behind that, and so it's very possible that I'm leaving some out. Almost certainly I'm going to leave some out. But of course reduced activity is part of it, and that affects your total energy expenditure in two different ways, right? So first of all, you're not as active, so that immediate expenditure is going down. Second of all, you're probably not loading your skeleton as much, and so you might be losing some fat-free mass, which of course, is the kind of primary predictor of resting metabolic rates. It's not a perfect predictor, but it explains more than anything else. So there's the reduction in activity that also impacts some body composition characteristics.

Speaker 2: 47:35

One other thing that they mentioned, I believe, was the possibility that at the age of 60 and beyond we start to actually see some tissue specific changes in energy expenditure. So, for example, um, you know we always talk about how skeletal muscle is this really? You know, um, you know this, this tissue that just churning through calories has this high metabolic rate. And if you want to increase your metabolic rate, put on muscle, but muscle is, I think it's what 13 calories per kilogram per day, it's resting metabolic rate. Put on muscle, but muscle is, I think it's what 13 calories per kilogram per day, it's resting metabolic rate. Heart and kidneys is 400, right, I mean, it's just in a completely different, completely different level. Now you're not going to have, you know, tens upon tens of kilograms worth of heart and kidney tissue. I hope you don't. That won't be good.

Speaker 2: 48:22

But nonetheless, I think one of the proposed mechanisms in that paper is that perhaps as we age we start to see some age-related changes in the metabolic activity of perhaps some of those organs which really do have a huge impact on our total daily energy expenditure. I mean, if you just look at liver, brain, heart, kidneys, even a small age-related decline in the metabolic activity of those organs would really have a measurable, detectable effect that would impact not only total energy expenditure but basal expenditure as well. So that could be something that links the findings of those two papers. So I think it's multifactorial and, as someone who I like to think of myself as being pragmatic, my question is always what are you going to do about it? Right, and so so, when people say, oh, I'm approaching 60 and things are going to get rough, I said, well, we still have the same levers to pull that we've had all along, which is, you know, all these different health behaviors we've alluded to previously, and the?

Speaker 2: 49:23

And the reality is, um, if you are lucky enough to live into your sixth, seventh, eighth decade of life, yes, your fitness goals start to become more about keeping what you have rather than gaining what you've never had. Um, but I I prefer to view that as a privilege of living, to see the day that that that you're, you know, fighting a different fight in terms of your fitness level, and it's still a noble fight to, to, to embark on.

Speaker 1: 49:51

Yeah, I think. I mean obviously age always wins.

Speaker 1: 49:55

This is really more of an academic discussion. Tony and I are still going to be working out like crazy, hopefully slowing down some of these processes, but at the end of the day, you know, I'm looking at this figure and there's a few people who are close to 100. And I'm thinking, hey, if I can get close to 100 and be active and, you know, functional, hey, I'll be happy. But you know, it's like my primary, you know, exercise training is paddling, you know, and one day I'll get Tony out there, but he might sink to the bottom if he falls off. But the one thing that I like about it is that I know, from a purely physiologic standpoint, I'm not going to get better. However, from a skill standpoint, I can get better.

Speaker 1: 50:37

So I think, it's just like if I was a distance run, it's like you know what, I'll just be slower every year. But at least with this, the skill component and Tony knows, even the skill component is good for maintaining cognitive function. When you, when you challenge your brain with a, you know, with an exercise that's fairly difficult, you know, I'm like, okay, I'm glad I picked this, because if it was some other, less skilled type exercise, it would just be, it would be age 60, 61, 62. And I'm like this low decline, it's like, oh my God, that's gotta be depressing. Yeah, I think I think about it.

Speaker 2: 51:11

Yeah, I mean, I think about aging all the time. I mean, as I'm, you know, getting into my, my thirties and you know I'm like, okay, well, I see where it's going, uh, if I'm lucky, Right. And I think, okay, well, I see where it's going if I'm lucky. When I think about aging successfully and enjoying the aging process, I think about how am I going to change the way I engage with exercise, Like you said, picking new skill-based forms of exercise, that kind of check those boxes for physiological demands?

Speaker 2: 51:42

That's a great way to do it. Another way something I think is great about different strength sports is that they typically have masters categories. You know, masters one, masters two, and so even then you're saying, okay, I'm not going to set the PRs that I, I'm not going to break the PRs that I set when I was 28 and lifting three hours a day, and, you know, not a care in the world. But if I'm able to maintain my strength better than everyone else in the 70 plus category, I'm still winning right and I still have that bar to shoot for.

Speaker 1: 52:12

Eric, you're going to laugh at the age category I compete in. Just get ready for this. I compete in the 60 to 100 age group category. Broad range, yeah, you know, like holy shit, I'm competing against 90 year olds. This is great yeah.

Speaker 3: 52:30

That's half a century in a category.

Speaker 2: 52:34

That's right, I think. I think you need to grow the sport. Get some more and more people to enter into the master's races. They'll start chopping that up a little bit.

Speaker 1: 52:42

I think so. I think so. Um, the masters races they'll start chopping that up a little bit, I think so. I think so. Um, hey, we want to be respectful of your time, tony, if you have any final questions or comments for eric, because this has been just to really thank you, eric.

Speaker 3: 52:51

This is fascinating. I look forward to sharing it with my students the work you're doing, and I just think it just shows the the incredible adaptive capacity of the human body. It adapts to things in ways we still don't understand and it adapts to things we never, thought it could. It's really pretty amazing what a great discipline in science and really happy to have your work available to all of us. It's great.

Speaker 2: 53:16

I appreciate that.

Speaker 1: 53:17

Yeah, thank you, dr Eric Trexler, duke University postdoc. It's been a pleasure, so enjoy the rest of your days. Thank you, appreciate it. Thank you, yeah.