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Why Is This Happening? Examining energy and evolution with Herman Pontzer: podcast and transcript

Chris Hayes speaks with associate professor of evolutionary anthropology, Herman Pontzer, to shed light on how our bodies have evolved to use energy.

How does the human body take in and use energy? It is a simple question, but one that we still do not have a definitive answer to. This week associate professor of evolutionary anthropology, Herman Pontzer, joins to shed light on these evolutionary mysteries. How did our bodies get to be the way they are? And how do we keep ourselves happy and healthy in the modern world we have built?

Note: This is a rough transcript — please excuse any typos.

CHRIS HAYES: One thing that I got from your work that really blew my mind was the idea that okay, well I know that we have bigger brains than other animals and that’s our special thing, right? But you make the point that there had to be a kind of metabolic miracle. There had to be this jump in our energy processing systems to create essentially the extra brain energy budget necessary to become humans.

HERMAN PONTZER: Yeah, that’s right. So, to be able to fuel all these expensive traits—big brains, big babies, physically active lifestyles, right—

CHRIS HAYES: Big brains and big babies is an amazing way of describing homo sapiens.

Hello, and welcome to “Why Is This Happening?” with me, your host, Chris Hayes. Well, it's a beautiful day, it's a beautiful spring day in New York City and I'm vaccinated and a lot of people I know are vaccinated. Spring is always a time when we kind of emerge from winter quasi-hibernation, particularly in the parts of the country that get cold, like the Northeast where I live or the Midwest where I used to live. There's been a special hibernation that's happened with COVID, people have jokingly referred to the “COVID 19,” meaning the 19 pounds they packed on during their inactivity during COVID. But I think that it's fair to say that most of us were more sedentary than we'd normally been for a long period of time.

Gyms were closed, for one thing. There's a lot of people who get their exercise that way. That's the way that I tend to exercise is go to a gym. So gyms were closed. I know people who really, really missed that activity. And then particularly during the winter, when it's cold out, I would find myself, you got that little step tracker on your phone or if you have a Fitbit or whatever, it tells you how many steps you take. I'm a walker, I live in New York City and I love to walk and I do my editorial meeting every day just like walking around the park, particularly when it's nice out.

But during that COVID winter, it was really bleak. I would look at the end of the day and it was like, I took 3,000 steps all day, because what did I do? I sat in my apartment all day. I go to the office at night to do the show. You're not going out anywhere, you're not meeting people for things. I'm not even walking the kids to school because they're in Zoom school.

So the amount of physical activity that we all experienced I think declined, and I think it probably messed with our mental health a bit. I'm speaking personally, it definitely did for me. And that relates to another question, which is just about the nature of the sedentary lifestyles that we tend to live, or certain sets of people in the developed world do. Now I should be clear, there's lots of people who do extremely physically strenuous activity in the United States, which is one of the richest countries in the world. There are people who do construction, there are people who are on their feet all day. I waited tables and I know that's physically extremely strenuous. There's nursing assistants, home healthcare, on and on and on, farm workers.

But it is also the case that as an economy gets more developed, there's a shift in the kinds of labor and activity of folks. People tend to get cars more and there tends to be more essentially sedentary jobs because you have sort of more knowledge and knowledge work, as it's called. And when that happens, you start to see declines in activity, not just here in the U.S., but in other places as well. And there's a sort of interesting question that happens, which is about the ways in which our bodies adapt to that, and the fact that obesity, particularly in adults and childhood obesity, also tends to go up as a country gets richer. We see this in the U.S., this is something that has been written about a tremendous amount, but it's happened in other places, too. Mexico is a good example. We’ve seen, as the per capita GDP increases, you see a corresponding increase in obesity.

Now, there's a question there about what's happening with respect to that, why is that happening? And the way we tend to think about this is this sort of ledger, with diet on one side and exercise on the other. And you have heard diet and exercise, diet and exercise as a kind of health truism most of your life. What you put in your body, what you eat, and how much you move are two basic things that have a lot to do with our health, although are not determinative in any way. People have all kinds of different health conditions through their genetics or chronic conditions, et cetera.

But there's a really interesting sort of mystery at the core of this question of how does the body—simple question—how does the body take energy in, use it, and then what does it do with that energy? And it turns out, we don't have a definitive answer to that question. There are a lot of mysteries embedded within that. But there is some incredible work that's been done on the activity part of this. How does the body take energy and use it in our body? What does it use it for? How dynamically does it control it? What happens if you suddenly increase the amount of exercise you do? What does your body do with the fact that you have now more calorie expenditures? And it turns out, our bodies are miraculous evolutionary innovations on exactly this plane in the way that we use energy.

And one of the people who's done some of the most incredible work on this is Associate Professor of Evolutionary Anthropology at Duke named Herman Pontzer. He's got a new book out called “Burn” that sort of goes through his work. But it caught my eye a while ago and I've been really fascinated by his discovery, so it's a great honor to have Herman on the program.

CHRIS HAYES: So can you tell me first I guess what your field is and what kind of work does one do in that field?

HERMAN PONTZER: I study human evolution. I want to know how the body got to be the way it is, the millions of years of evolution that shaped the way our bodies work. And I'm particularly interested in what all that means for today and how we keep ourselves healthy and happy today in our weird modern world that we build for ourselves. And that can mean a lot of different things, people who study human evolution can focus on a lot of different things. I focus on energy expenditure because that's one of the places where the rubber really hits the road in evolutionary biology, is getting energy from your environment and using it for all of life's essential tasks: growth, maintenance, reproduction, especially reproduction because, from an evolutionary point of view, life is a game of turning energy into kids.

CHRIS HAYES: I've heard you say that line before. It's worth pondering on that for a second. Life is a game of turning energy into kids. What does that mean?

HERMAN PONTZER: Evolution, natural selection, it favors strategies—that might be an anatomy or behavioral strategy or kind of physiology—that is better at consistently getting energy from your environment and using it for reproduction, because the scorekeeping in evolution is how many successful offspring do you have. People talk about survival of the fittest. Survival only really matters in evolution if you are surviving to be able to reproduce. It really comes down to how many kids you're having because if more of the kids in the next generation are your kids, look like you, have your genes, then, in the scorekeeping of natural selection, that puts you ahead.

CHRIS HAYES: My favorite example of this is the fact that the human move from hunter and gathering to stationary agriculture was basically a massive disaster for human flourishing, happiness and created mass misery. We basically were healthier and lived longer when we were hunter-gathering, but for essentially a kind of evolutionary reasons, we end up yoked to agriculture because it works for both for the seeds that we're planting and for us, which actually causes us to have more children because we're stationary and because people are dying so much, they need kids to take care of them. But it actually isn't a net increase in happiness.

HERMAN PONTZER: No, it isn't. So I get to work with some of the last groups of hunter gatherers on the planet right now, which is really a fun piece of my job. But if you ask them how happy they are, and people have studied this, they're actually happier, the hunter-gatherer group we work with, on average than most other populations around the globe. So there has been no net increase in happiness over the last couple million years, I wouldn't say. But there has been an increase in how many kids you can have if you go from hunting and gathering, where energy is scarce, to farming, where energy is more plentiful.

CHRIS HAYES: Right, and that's it. Evolution doesn't care about your happiness. Evolution cares about how many kids you have.

HERMAN PONTZER: That's right. That's exactly it.

CHRIS HAYES: So I want to talk about this idea of just energy and energy budgets in biology because I think in mechanical and technical spheres, in engineering spheres, we think about it all the time. It actually weighs on our mind all day because we have a phone battery and we're thinking all day about where's that phone battery and if you're ever out on the road or you're covering something in the field, you don't have the battery, you're stressed out by the fact that the battery's low. And we understand that a car, you’ve got to get the energy inputs, and then the output is driving, and it runs down. But that's true of every form of life on Earth. What are the contours of understanding the basic parameters of energy budgets and energy maintenance and usage in biological entities?

HERMAN PONTZER: There's a bunch of interesting kind of comparisons and analogies there. I think to start off, we have to realize that your body is spending energy on all sorts of tasks throughout the day. You've got 37 trillion cells, all of them like little microscopic factories chugging away, and all of them are using calories. And so, most of the energy that you burn every day isn't on the stuff that you're aware of, like movement. Most of it's on things like your brain and your liver and your kidneys and your immune system. And so, even if you're an active person, most of your energy is spent on these kind of unseen tasks. So you bring energy in, which is sort of recharging your battery, and then you spend the energy out on all these different tasks. And in that sense, we are kind of like a battery that you can recharge.

But what's really interesting about humans, and another animals, too, is that your phone can't kind of prioritize or decide to spend energy on one task versus another. It doesn't really have that kind of adaptive capability. But your body does. And so, that's the kind of big advance in this field of metabolism over the last decade or so, is just how adaptive and dynamic your body can be in how it spends its calories.

CHRIS HAYES: So let's talk about the key concept here of metabolism. Metabolism is one of those concepts where I don't actually understand what it means. I obviously use it because it's in common usage to be like, “Oh, he has a high metabolism” or “I'm metabolizing.” But I don't know, what is a metabolism?

HERMAN PONTZER: Metabolism is all the work that all your cells do all day. So again, your cells are like little microscopic factories, they're bringing nutrients in, they're doing stuff with it, they're getting waste products out, they're signaling other cells. They're busy all day, all 37 trillion cells. And all of that work that they do takes energy, just like any kind of work takes energy. And so, we can either measure the work, we could actually measure the nutrients that are going in and the products that the cells make, and some people do that, they measure, when they talk about metabolism, some researchers are talking about looking at the actual products that the cells make.

But the other way you can do it is you can do what I do, which is measure the energy expenditure of those cells. And so, when people talk about your metabolism, they're talking about the energy that you burn every day, the calories that your body is burning off all day.

CHRIS HAYES: So, my understanding is, part of your work focuses on a kind of evolutionary leap that happens in the dynamism and/or efficiency of our metabolic systems compared to our primate ancestors and relatives. Is that right?

HERMAN PONTZER: Yeah. So, there has been a big change in human evolution, in the way that our bodies burn calories. We have ramped up our metabolic rates. Our cells are busier. We burn more calories every day than our ape relatives do. That's because of all these really expensive traits that we have, these big expensive brains. So your brain, Chris, your brain burns 300 kilocalories a day, which is the energy equivalent of running a 5K. And an ape, a chimpanzee, has a brain that's only a third of the size, so they're only burning a third of those calories. So, things like that, things like the fact that we are physically active, humans have big babies quite often compared to other apes. All those things take a lot of energy. So we've actually increased our energy expenditure as a species compared to other apes.

CHRIS HAYES: In an evolutionary sense, these traits are being selected for that are more and more energy intensive, and perhaps most importantly, is these brains that use a huge amount of our energy, right? And one thing that I got from your work that really blew my mind was the idea that okay, well, I know that we have bigger brains than other animals and that's our special thing. But you make the point that there had to be a kind of metabolic miracle. There had to be this jump in our energy processing systems to create essentially the extra brain energy budget necessary to become humans.

HERMAN PONTZER: Yeah, that's right. So, to be able to fuel all these expensive traits—big brains, big babies, really physically active lifestyles—

CHRIS HAYES: Big brains and big babies is an amazing way of describing homo sapiens.

HERMAN PONTZER: My first album is going to be “Big Brains and Big Babies,” that's what we're going to do. Yeah, that's it, that's human evolution in a nutshell. How do we do it? How do we get away with it? What's the forensic accounting on that? How do we afford it? And the answer is, we have changed the ways that our cells burn—we basically ramped up, we've turned the dial up to 11 so that we can burn energy faster and use energy faster than other apes do. And another piece of that is, that's great, you turn the engine up faster. Well, how do you get the energy in faster? And the way that we've done it is we've changed the way that we get our food. This has been the big-C Change, the big leap forward, like you said, in our evolution, is this behavioral change in how we get our food. We hunt and gather. All the other apes just gather. But we hunt and gather and we have this kind of mixed strategy.

What other species—forget primates, what other species of any animal in the world has half of the animals, half of the population goes out and gets one kind of food, half the population goes out and gets a completely different kind of food, and they have all these different kind of risk and reward, variables in these different kinds of foods, plants versus animals? And then they bring them back at the end of the day and they share them? That is a genius strategy and that was the kind of the killer app of hominid evolution was hunting and gathering. And that allowed us to ramp up our metabolic rates the way that we've needed to do it.

CHRIS HAYES: I see. So it's not that we're more efficient, it's actually just that we have bigger budgets and then we come up with strategies to feed the budget with more energy. We basically just like, we're adding lots of cool things to our abilities that just take a lot more fuel, but then we're coming up with ways to get a lot more fuel. And your point there is that hunting, that our primate ancestors or relatives, they just gather. They go around and they grab food where they find it, right?

HERMAN PONTZER: Yeah.

CHRIS HAYES: There's two key things that we do: a division of labor, some people go hunt, and some people will gather, that's the gender breakdown, usually, I think in hunter-gatherer societies. And then, pooling the resources and sharing them, and these are specific, evolutionarily adaptive strategies for increasing total amount of kilocalorie intake.

HERMAN PONTZER: Yeah, that's right, because you think about what you're doing when you diversify your food portfolio like that. You've got some folks, and usually it is gendered. Not always, but often it's gendered. And often, it's women who are going out and getting plant foods. And the great thing about plant foods is they don't run away, there's a bunch of them on the landscape, they're dependable. And you're going to come home every day with a ton of calories from plants.

And then you have other folks, which often is, but not always, is men who go out and hunt. That's a kind of a risky strategy because you might come home empty-handed. In fact, we work with a hunting and gathering population called the Hadza in Northern Tanzania. Men there, they hunt with bow and arrow in this savanna habitat. They're hunting zebra and giraffe and kudu and big antelope. They get big game about once every 30 days of hunting. They get smaller game much more often, but big game that you could bring home and really feed the camp with, only once every 30 days or so.

And so you're often coming home empty-handed. Well. But there's lots of fat and protein and nutrition in those animals. And so, if you combine those two strategies, you get to take the big risks, think about this in the economics world, you get to take the big risk because you can come home every day to at least the sure thing of the plants, but you also get the big reward when you hit on a zebra or a giraffe.

CHRIS HAYES: It's really wild. I had never thought of it this way, but it's like a stocks and bonds portfolio, right?

HERMAN PONTZER: Yup, absolutely. It's a 60-40.

CHRIS HAYES: Yes. So bonds are fixed income. They're fairly dependable. They're fairly low risk and low reward. And equities, stocks, are higher risk and high reward. You combine them in the portfolio so that you have some baseline stability with lower reward, and then you have more risky stuff, and hopefully, when those come together—and what you're saying is the hunting gathering is the stock bond 60-40 portfolio of, essentially, human development.

HERMAN PONTZER: Yeah, that's it. And it's such a world beater that it is—I mean, it's the reason that we're the dominant primate, the dominant species on the planet. You can't beat it, actually. And what's crazy is, you were talking about how we have these expensive traits and we needed to find a way to fund them. Actually, it's the reverse. So the behavior has to come first. Evolution doesn't work like Wall Street because you can't leverage your future. There's no mortgaging going on. You have to pay for it today.

CHRIS HAYES: Of course, of course. So behavior is what happens, the behavior change.

HERMAN PONTZER: Yeah. The behavior changes and everything follows along.

CHRIS HAYES: I see. So we figure out the hunting-gathering and that facilitates the physical traits?

HERMAN PONTZER: Yep, absolutely. And think about this: we're the only primate that shares the way that we do. You and I, back when we used to go to work, you might share a lunch. Back when my kids were allowed to share lunch at school, they might have shared lunch at school. But you've got birthdays and barbecues and it always involves sharing food. And why is that? Well, because that's what humans do. We think it's normal, it's crazy. No other species shares food with people they're not related to, but we do it as a rule and we've been doing it for two million years since we started hunting and gathering.

CHRIS HAYES: And one of the parts of that, too, is that the reason hunting is kind of a strange thing to do for our species is that if you're a human and you kill an antelope, you can't eat that antelope. You need to share it. And there's a relationship between the fact that we're hunting this big game, and then occasionally hitting on it, but then you’ve got to share it then, right?

HERMAN PONTZER: Yeah. Nobody can eat a zebra by themselves or even a big antelope. So that's exactly right. The big game hunting goes along with this. So many pieces of what we kind of think of as normal, or traditional, or ancestral, these are all, they all revolve around how you get your food, how you get your energy, how you spend that energy, which again, this is why I'm so excited about this stuff, as somebody who studies human evolution, because this is where all the action is.

CHRIS HAYES: So, this hunter-gathering innovation, which is behavioral innovation, enables a durable and sustainable level of energy intake that then facilitates the evolution of highly expensive, in energy terms, traits that we have, right?

HERMAN PONTZER: Yep.

CHRIS HAYES: Okay. So, let's talk a little bit about some of the work you've done with the folks you work with, the hunter-gatherer tribe. And can you just tell us a little bit of who they are, where they are, what their life is like and what your scholarship with them has been like?

HERMAN PONTZER: Sure. The group that I work with that are called the Hadza and they are a hunting and gathering population in northern Tanzania. They’re one of the last hunter-gatherer populations left on the planet. So by hunting and gathering, what we're talking about here is no crops, no domesticated animals, no guns, no machines, no electricity, no plumbing. They live in grass huts in the middle of the savanna in small camps. Every morning, they wake up in the morning and they get food that day. That's kind of the rhythm of their life is up in the morning with the sun, women go out to gather plant foods, which can be berries, or they might dig for wild tubers, wild root vegetables.

Men are up and they usually go out alone. Women tend to go out foraging in groups, but men like to go out by themselves to hunt with bow and arrow. And like I said, they'll hunt anything from zebra to giraffe to smaller antelope and smaller animals. Men also gather honey. There's a lot of potential to get honey out there. Wild bees will make their hives in the hollows of these tree branches. And so, they'll go up and chop into the branches and get out quarts of honey at a time. 15 percent of the Hadza diet in terms of calories can be honey in any given week or month.

CHRIS HAYES: That's extremely calorically rich, right? That's like gold.

HERMAN PONTZER: Absolutely. That's exactly right. And they've been doing this for millennia, for as long as anybody's been paying attention, and we think back probably thousands and thousands of years.

CHRIS HAYES: What is the rhythm of that day like? This is a naïve and ignorant question, but I'm just going to ask it: is it like a work day? Is it broken up into different shifts, is it the same time every day?

HERMAN PONTZER: There's no electricity and you're on the equator. So the sun comes up at six and goes down at six every day—6:30, let's say. And it gets hot in the middle of the day. As soon as the sun's up, you're up. You get started on your day before it gets too darn hot. And women are often back in camp by sort of noon or so with whatever plants they've gotten. They'll start preparing that food and sharing it with the kids and whoever else is in camp. Men will spend the day out hunting, the whole day out. Sometimes, they spend a day in camp to kind of recuperate or build arrows or build bows, that kind of thing. There's not shifts. I will say this, it's egalitarian, so there's nobody in charge of anybody else. Men can't tell women what to do or vice versa. There's no chief, there's no police. There would be nobody to enforce a shift structure. Everyday kind of feels very similar, day after day.

CHRIS HAYES: This sounds like a fairly physically strenuous day for everyone involved.

HERMAN PONTZER: Incredibly so. We've measured this now. We use accelerometers, which are basically like step counters. We've also done it with heart rate monitoring. And the punchline is that they get more activity in a day than most Americans get in a week.

CHRIS HAYES: Really?

HERMAN PONTZER: Yes. Yes. It's five to 10 times more activity, depending on time of year and that kind of thing, but yeah, that's basically it.

CHRIS HAYES: Wow. And how many calories a day are they eating?

HERMAN PONTZER: Well, we know this because we've measured how many calories are burning when they’re weight-stable. And so if you know how many calories they're burning when they're weight-stable, you know how many calories must be coming in. And this is the crazy part—

CHRIS HAYES: I want to stop before we get here. Let's take a commercial break. This is, I’m a professional here. Take a commercial break. I want you, during the commercial, think of, okay, if an American with an office job burns, what, 2,000 calories a day, somewhere like that?

HERMAN PONTZER: It's more like 2,500 a day.

CHRIS HAYES: 2,500 a day. Say an American with an office job burns 2,500 calories a day. I want you to take a guess during this commercial break of how many calories a day these hunter-gatherers who are getting five to 10 times as much activity a day are burning a day. We'll be right back.

Okay, so, they're walking miles and miles and miles. They have hugely strenuous, physically demanding lifestyles because they are literally expending, they're basically expending all their energy to get the food that they then recoup. It's an elemental equation. And so you start to study them. Before we get to it, what was your hypothesis about how many calories they were burning?

HERMAN PONTZER: Oh, I knew what we'd find. I knew it. I knew that they'd be burning tons more calories than we do because there's so much more physically active. In fact, before we did this project, nobody had measured energy expenditures in hunter-gatherers, had never been done. And it's because you need to use this technique which was only kind of recently developed, this isotope-based technique called doubly labeled water, and I won't bore you on the details, I'm happy to go into it if you like. It's the gold standard way to truly measure calories expended in people who are outside of a laboratory in their normal daily life. And nobody had ever done this measurement in hunter-gatherers before.

And so, a couple of my colleagues and I—Dave Raichlen, Brian Wood and I—decided we're going to go and do this. We're going to get these first measurements because I love to think about energy budgets and I want to know what the energy budget really looks like for a hunter-gatherer.

CHRIS HAYES: Give me the 60-second amateur version of how this doubly labeled water isotope thing works.

HERMAN PONTZER: Sure. All water is H2O, correct?

CHRIS HAYES: Yes. I agree. That I know.

HERMAN PONTZER: You agree. So you drink some water that has isotopically tagged H’s and O's. We can watch the H's and O's flow through your body. And the H's flow through your body with water, water that comes and water that you excrete as urine or sweat. The O's take that same track because there's O's in your urine in your sweat as well, but the O's are also lost in the CO2 that you breathe out, the carbon dioxide that you breathe out. If you drink this isotopically tagged water and then we collect urine samples over the course of about a week, we can watch those two isotopes flow through your body and the O's are lost faster. The amount by which they're lost faster tells us how much CO2 you're making.

CHRIS HAYES: There you go. The CO2 is the engine exhaust of the energy conversion.

HERMAN PONTZER: Exactly. You cannot burn calories without making CO2, you cannot make CO2 without burning calories.

CHRIS HAYES: Gotcha. So that must give you a fairly precise reading.

HERMAN PONTZER: Incredibly precise. This is the gold standard. If you were to go down to Mount Sinai Hospital or any other of the leading nutrition metabolism centers in the world, and they want to know how many calories you're burning in your normal daily life, this is what they would do for you.

CHRIS HAYES: And so, what was the answer?

HERMAN PONTZER: The answer is Hadza men and women burn exactly the same amount of energy that we burn in the U.S.

CHRIS HAYES: It's a nonsensical finding.

HERMAN PONTZER: It's completely nonsensical. We were shocked. It gets even crazier because they're a bit shorter than us. On average, it's a short-statured population, and so, it's actually even less. Women are burning 1,800 calories a day, men burn like 2,400 calories a day, whereas women in the U.S. burn about 2,400 calories a day, men burn about 3,000. Anyways, if you account for body size, because big people burn more calories than small people, okay, you account for body size, account for gender, account for age, account for fat percentage, all that stuff, does not matter. They're burning exactly the same number of calories every day as you and me.

CHRIS HAYES: Okay. When I first encountered this finding in the research in your writing, it seemed like it violated the second law of thermodynamics. You know what I mean? Energy, it's got to come from somewhere. It seems like they're defying the laws of the universe. How can it be the case that if they are doing five to 10 times as much activity and they are out at dawn hunting game, slugging it back, and I'm sitting here at my dumb ass computer, scrolling through Twitter, how can it possibly be?

HERMAN PONTZER: I'm with you, man. When we first got those results back, I remember looking at my computer screen and just shaking my head and being like, what the heck is going on? I looked at it every which way I could, I was sure I was doing something wrong.

CHRIS HAYES: Right. You must have said, “We screwed up the isotope thing.”

HERMAN PONTZER: Absolutely. So now we do these analyses in our own lab, but at the time, I was collaborating with one of the best labs in the world, Bill Wong’s lab at Baylor. And I emailed Bill and I said, “Bill, are you sure? Are you really sure? Is there something that we messed up?” And he said, “No, these are really strong data.” He said, “These look better than most of the data that we get in the lab here at Baylor.” And I can tell you why. That's because we had really great participants who were happy to be part of the study, which was, it's a testament to how cool the Hadza are.

Anyway, we were really sure that we messed up, so we did a few things. First of all, we used a completely different method to double check. And so, like I was telling you before, we have heart rate monitoring that we do with these guys. They wear like a chest strap, like a jogger heart rate monitor that people wear if they go out and run a lot, they might track their heart rate that way. We had those, we had heart rate-based measures of energy expenditure. hey gave us the same answer. We have since done this in other populations: two populations in the Amazonian rainforest, other populations, we have a new group that we're working with in northern Kenya. Same answers again. People who are really physically active are not doing what they're supposed to be doing and are not burning more calories than you and me.

CHRIS HAYES: So, how? How?

HERMAN PONTZER: So, that has been my research career for the last decade since we got these results because, as a scientist, that's what you hope for. You hope to get surprised, you know? There's nothing better than that, because if you're just getting the results you expect all the time, then that's nice and it feels good, but you're not learning anything. And so, what these results said is we have something really kind of fundamental to learn here about how the body works. And so, we've spent the last 10 years tracking it down and here's what we know so far. First of all, it's not just the Hadza. Other human groups are like this, too. Second of all, it's not just humans. And so, we see this in lab experiments, in mice, in rats. We see this with other primates, for that matter. If you have one group of mice that are really active and one group of mice that are sedentary, same energy expenditures. If you have primates, monkeys in the zoo versus monkeys in the wild, same energy expenditures.

So this is a really fundamental thing about how evolution has shaped mammals and birds, maybe other animals, too. And it seems to be that your body is able to adjust to lifestyle, it can adjust to how physically active your lifestyle is, so that if you are burning lots of energy on activity, it reduces energy expenditure on other stuff to kind of make room in the budget for that activity and keep the top line number of calories the same.

CHRIS HAYES: So this is the key conceptual point I just want to hammer home, which is that we think of activity and what our body is doing in terms of physical activity. So if I think like, “What did I do today? Well, I worked out or I walked 15,000 steps or I went for a run,” right? In the budget of the energy you expended that day, that's what, 15 percent maybe, that’s 20 percent, somewhere in there, right?

HERMAN PONTZER: Yeah, well, something like that. Let's say the exercise that you went to the gym to do is 15 percent maybe, and then the rest of the movement that you did just to kind of move around your apartment, go get on the subway, walk around the park, maybe that's another 10 percent or so.

CHRIS HAYES: There's a huge amount of other processes burning energy that the body has to work with in a budgetary sense to compensate for express physical exertion.

HERMAN PONTZER: Yeah, that's exactly right. Yeah. So you've got your immune system, you've got your reproductive system, you've got all of it. All of it is available to be modified to keep the numbers the same.

CHRIS HAYES: But what does that modification look like? What does it mean to devote less energy to my immune system?

HERMAN PONTZER: Right. It sounds bad, but actually—so this is one of the really exciting things that's come out of this work—this seems to be one of the really important reasons that exercise is so good for you. Okay, so, here's what we know. If you take somebody who is really sedentary and you get them exercising, what happens? Things like inflammation, which is your immune system being overactive, goes down. Your reaction to stress, so the cortisol level, the adrenaline levels that you spike after you get stressed out, they don't go up as high if you're somebody who exercises regularly, and they come down faster.

Reproductive hormone levels—so estrogen and progesterone for women, testosterone for men—they are sky high in a population like your typical men and women in the U.S. They're at a healthier level in populations that are more physically active. And so, we're starting to connect the dots here. We don't have it all sorted out entirely, but we're connecting the dots here and saying, look, these adjustments that the body's making to physical activity to reduce expenditure elsewhere, they're actually really good things, for the most part. You can push it too far, we can talk about that. But for most of us who aren't Olympic-class athletes, exercise is doing good things for us. It's keeping us in a better place because it's regulating these other expenditures.

CHRIS HAYES: That's so fascinating. So it's like the other expenditures, the homeostatic equilibrium that they're pegged to from an evolutionary standpoint, which is hunter-gatherer, is such that that equilibrium is pegged to a fairly high level of physical activity. When we don't do that level of physical activity, we then burn more calories on the other stuff, is that right? And we don't need to, and so it creates sort of weird effects?

HERMAN PONTZER: Yeah, that's exactly, exactly right. And you've got the right thinking there, which is that, you can think about all these processes as competing for calories over the course of the day. And normally, low priority things like having a really high inflammation response or having a high stress response, those get tamped down in a highly active population like we've all evolved in. But now, you move to these weird zoos that we've built ourselves, where you don't have to be active, food's available all over the place, energy supply is really easy. And now, these low priority activities which used to probably only happen very occasionally in the past, in the deep past, now are happening all the time, chronically, at these super high levels, and it's actually really bad for you.

CHRIS HAYES: That's so fascinating. But then the flip side of this, which is the thing that we're all obsessed with, I think, in America, which is weight. There's a fascinating, real concrete ramification for someone like myself, who like, I am someone who, I think people have very easy relationships—there are some people who have very easy relationships to weight in their body and food and exercise. And then there's really tortured ones and I'm neither of those. But I definitely think about it and I work at it and I think about what I eat, and I think about how much I exercise, and I'm trying to kind of keep those things in a very effortful fashion in some kind of equilibrium, and I'm on TV every day and I hate the way I look on camera, yada, yada, yada, yada.

And so, for people in that world, who are not dealing with scarcity and they're not hunting and gathering, this unlocks this key secret, which is like, if you just start exercising a lot, your body just going to readjust. So it's good for you, but the idea that you're going to lose a lot of weight from doing it seems like that's not going to happen.

HERMAN PONTZER: No, that's right, because if you exercise, you start your exercise program tomorrow, then yeah, tomorrow and for a few weeks, maybe in a couple months, you'll burn more energy than you were before you started because it takes a while for your body to adjust. But after a while, your body's going to go, “Oh, okay, this is how much activity I can expect every day. And so, let me titrate these other things down a bit. Let me suppress some of this other activity bit.” Hey, that's really good for your health. You should exercise, you absolutely have to exercise, it's really good for you. But that weight change is going to stop because now you're back at equilibrium where energy in and energy out is the same as it was before and you're going to stop losing weight at that point.

It's one more reason that exercise is a poor tool for weight loss by itself. Now, it can be a really good thing to sort of add to a diet. It can be good for weight loss maintenance once you've lost the weight. I'm not saying that there's no role for exercise at all, but it's a pretty minimal one for weight loss.

CHRIS HAYES: Yeah, that's so fascinating. And I think that lesson has gotten integrated into mainstream annoying nutritional diet advice. “Bulk in the gym and cut in the kitchen,” as they say in sort of the annoying parlance of the world of weight training internet culture. But this sort of unlocks something really profound about our bodies, two things. One is like, exercise is not going to be the thing that is going to have you lose weight over a long period of time. And two, exercise is really good for you for a bunch of other reasons because of what it's doing to the energy budgets and the processes in all kinds of other areas of your body.

HERMAN PONTZER: Yeah, that's exactly right. And I would say, what is it, “bulk in the gym and cut in the kitchen,” I haven't heard that version of it. Some people have heard that before. But if you go to the WHO fact sheet on obesity, you go to the CDC's guidelines for obesity, you go to the UK's National Health Services, they all have this message that says if you want to fix obesity, then it's diet and exercise. It is the same bullet points, same breath, and there's no distinction about oh, actually, you're going to get almost all of your benefit in terms of weight from diet and exercise is important for other reasons. It's never phrased like that. And I think if we don't address the public health messaging on this and get really clear about what exercise is so good for, but also what it's not that great for, it's going to be harder to get people on board with what we need to do.

CHRIS HAYES: Yeah, so your point is that the way that this is seen by mainstream public health organizations across the world and the U.S. is just, it's just a simple ledger. Calories add and exercise subtracts. And what your research points to is, exercise doesn't really subtract at a certain point. Pretty quickly, the body just stops subtracting.

HERMAN PONTZER: Yeah, that's exactly right. Exercise, even when you have it supervised—so lots of great labs have done long term studies where they get people exercising and the people who are in those studies, they have to show up at the gym and people watch them while they exercise, and it's all supervised, nobody's cheating. And people don't lose weight. They stop losing weight, maybe they lose a couple of pounds, but it's nothing like you'd expect them to lose based on how many calories they're burning in that exercise. And so, even if in a perfect world, exercise alone just is not going to do a lot for your weight.

CHRIS HAYES: So what are the broader implications? I mean, we get these high-level issues. The fundamental thing here is that our bodies evolved for scarcity and we live in abundance. That's an oversimplification, but that's sort of the way it is. Our bodies evolved, as the vast bulk of human life on the planet, as hunter-gatherers. Agriculture and then civilization, and certainly modern civilization, which, there's incredible energy inputs from fossil fuels, are an eyeblink in the time that our bodies have been on the planet. And so, that's going to create some pretty haywire stuff.

HERMAN PONTZER: Yeah, absolutely. There's lots of things to tackle here. We need to think about how we're going to clearly message what we hope people will do if we're going to try to fix things like obesity or heart disease, diabetes. Even in the midst of a global COVID pandemic that has killed millions and is this enormous human tragedy, even so, this year, the last 12 months, heart disease, diabetes, obesity-related diseases are going to kill many more people than COVID did. And that's globally, that's not just in the industrialized world.

And so, if we're going to get a handle on the biggest public health crisis on the planet right now, obviously, we need to get a hold of COVID, but we cannot ignore these lifestyle diseases, which really fundamentally come down to diet and activity. And if we can get our messaging right on that and get the way that we engineer our world right on this, we can fix it.

CHRIS HAYES: So when you're talking about these lifestyle diseases, and what we're talking about is heart disease. My understanding of the literature, and I'm an amateur here, is that there's essentially a kind of monotonic correlation between economic development and heart disease across countries. Now, there's exceptions, like Japan, there's places that are above or below that baseline, but in the aggregate, the richer a place gets, the more we see that, right?

HERMAN PONTZER: Yeah, that's pretty much true. Yep.

CHRIS HAYES: And we think that is because of what's going on in the diet side, right?

HERMAN PONTZER: So obesity is going to be driven by the diet side and we can talk about aspects of food that make that happen. Heart disease is this interesting disease because it can be, your risk of heart disease goes up if you are overweight or obese. But you can also develop heart disease simply by being kind of out of shape and not active enough. That gets you both ways actually.

CHRIS HAYES: Wait, say more.

HERMAN PONTZER: So heart disease is associated with being sedentary and it's also separately associated with being obese. And so, obesity is related to diabetes, it's related to heart disease, it's related to all these diseases. But separately from that is also the activity piece. So you can't just do one or the other. You have to fix the diet piece and the exercise piece. But we need to have some clarity on how we're going to fix each one. So diet is the way we're going to fix obesity. Exercise and activity are ways that we can help fix heart disease and some other ones.

CHRIS HAYES: Right. So the takeaway here in some ways is, you kind of come back full circle, diet and exercise. It's just that the exercise portion is not going to be the solution for obesity. And this whole idea that sedentary lifestyles are what's driving obesity and we need to get kids more active so that they lose weight, or we need to get adults more active so they lose weight, you have strong biological evidence to suggest that's not going to happen. At the same time, a healthier diet to reduce population-level obesity—and I don't mean in specific cases of a specific individual, just population-level—and more exercise are both good healthy things that we want to encourage and facilitate, particularly in countries that have high degrees of heart disease or other lifestyle illness.

HERMAN PONTZER: Yeah, that's right. You have to think about diet and exercise as two different tools for two different jobs: diet for obesity and exercise for everything else. The reason I think we need to have that clear view is if you don't do that, then you get people who want to trade one for the other. So you get food industries that would love you to exercise more and ignore your diet.

CHRIS HAYES: Right, right. All the corn growers of America are like, “Drink that Coke and go for a walk.”

HERMAN PONTZER: Yeah, that's right. I love to watch football, and I watch football and they have the NFL Play 60 thing and that's great. Get those kids exercising. But you know who funds Play 60 is like Gatorade and Coca-Cola, because that's what they want. They don't want you to … “Hey, go ahead and drink the Coke and drink the Gatorade. Just make sure you go outside and play.” No, no, no, no, we’ve got to be clear about this. These are two different tools and two different jobs.

CHRIS HAYES: Herman Pontzer is Associate Professor of Evolutionary Anthropology at Duke. His book is called “Burn,” and it goes through this research. It's really just fascinating, mind-blowing stuff. Herman, thank you so much for joining us.

HERMAN PONTZER: It was so fun to talk with you, Chris.

CHRIS HAYES: Once again, great thanks to Herman Pontzer. He’s Associate Professor of Evolutionary Anthropology at Duke. His book is “Burn” and you can check that out right now.

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