The New Science of Metabolism and Weight Loss
Episode Stats
Summary
Dr. Herman Ponser is a Professor of Evolutionary Anthropology and the author of Burn: New Research Blows the lid off how we really burn calories, lose weight, and stay healthy. We begin our conversation with an overview of how metabolism powers everything your body does, from thinking to moving to simply existing, and how it uses the food you eat as the energy needed to fuel these processes. We then get into Herman s field research which shows that increasing your physical activity doesn t actually increase the number of calories you burn, but why it s still hugely important to exercise anyway.
Transcript
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Brett McKay here, and welcome to another edition of the Art of Manliness podcast.
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You hear a lot about metabolism. You probably know it has something to do with weight loss.
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And even if you don't go in for the supposed hacks around speeding up your metabolism,
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you likely figure you can at least increase it by exercising more.
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This isn't actually the case, though, and my guests will sort through this and other
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misconceptions around metabolism on today's show. His name is Dr. Herman Ponser, and he's a professor
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of evolutionary anthropology and the author of Burn. New research blows the lid off how we
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really burn calories, lose weight, and stay healthy. We begin our conversation with an
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overview of how metabolism powers everything your body does from thinking to moving to simply
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existing, and how it uses the food you eat as the energy needed to fuel these processes.
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We then get into Herman's field research, which shows that increasing your physical activity
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doesn't actually increase the number of calories you burn, but why it's still hugely important
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to exercise anyway. He also impacts whether certain kinds of foods are better for your metabolism,
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offers his recommendations on how to use diet to lose weight, and answers the common question
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as to whether it's true that your metabolism goes down as you age. After the show's over,
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All right, so your field research has uncovered some, I think, counterintuitive things about
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our metabolism, and we're going to dig into that today. But before we do, I think it would
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be helpful to do sort of a short Metabolism 101 class for our listeners. Because I think
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people throw around that word metabolism a lot, like, oh, I've got to speed up my metabolism.
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But they might not know exactly what that means. So what exactly is metabolism? And then we'll go
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from there. Sure, sure. So yeah, I think you're right. People kind of aren't always told the right
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thing. Metabolism is all the work that your cells do all day. So you've got 37 trillion cells,
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give or take, and each of them is a tiny microscopic factory that's bringing in raw materials. That's the
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nutrients in the foods that we eat and turning them into various molecules, hormones, that kind of
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thing, burning them for energy. And all of that work that our cells do, each of those little factories
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do, that takes energy. And so metabolism is all of that. It's all the work that's happening.
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And since work requires energy, we can think about metabolism either as the work itself. So people do
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focus on things like how molecules get changed around by cells. It's called metabolomics, the kind
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of products that they make. Or you can focus on the energy it takes to do that work.
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And that's what most people focus on in metabolism research, like me. We measure all the work that
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our cells are doing by measuring the energy that our bodies burn.
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Gotcha. Okay. So metabolism is the measurement of energy our body is using to do what it needs to do.
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Breathe, heart beating, reproduce, get off the couch. That's metabolism.
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Yeah, that's right. And most of it, you're only kind of dimly aware of or not aware of at all.
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So for example, every nerve cell in your body needs to keep a very precisely amount of negative
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charge inside of its cell relative to the outside of its cell, or else your nerves don't work.
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And so to do that, it's constantly pumping these ions, these sodium and potassium ions in and out
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to maintain that balance, maintain that negative charge. Your liver is constantly at work detoxifying
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all the stuff you ate, helping break down nutrients. Your spleen, your immune system,
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all of it, there's so many things that are happening. Your brain, your brain runs a 5K every
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day. Your brain burns 300 kilocalories of energy every day. That's the equivalent of going on a
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five kilometer run. And none of this you're aware of. You're only aware of the very small amount of
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energy that you spend relatively proportionally that you spend on things like exercise.
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Yeah. So that's, I think, an important point. I think people, when people typically think about,
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you know, speeding up their metabolism, and we'll talk about why that actually isn't a thing.
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They think, well, I just got to like exercise and move more and that's going to burn more calories.
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But you make the point like, no, most of your, the calories you burn, it's just functioning,
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just sitting there, existing, listening to this podcast.
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Exactly. Yeah. Yeah. I mean, even if all you did is binge listen to the Art of Man podcast
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all day, you'd still burn about, you know, 70% of the energy that you would have burned in an active
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day. So, okay. So I think you break it down. There's like a chart, like the kind of percentage
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of our calories that are, that we burn throughout a day that are geared towards just existing. And then
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there's movement. And then there's another one, another kind of criteria of how we burn calories.
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I think it's called NEET, N-E-E-T. What is, what is, what is NEET?
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Well, so NEET is this concept that, you know, you're kind of moving when you're not paying
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attention to it. So fidgeting, you know, standing up and walking over, you know, to get a cup of
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coffee, that kind of stuff. It's called, it stands for non-exercise activity thermogenesis.
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And it's, yeah, it's a nice acronym for, NEET is a nice acronym for that. And it's this idea that
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not only are you burning energy to move when you're paying attention to it and exercising,
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but you're also paying attention, you're also burning energy in these other ways as well.
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But there's even more than that, right? Because NEET's not to, okay. So NEET was kind of a concept
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that people developed because they were having a hard time making the numbers add up. When they
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would try to understand how people are spending their energy, they would look at basal metabolic
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rate. That's your energy at rest at like, you know, six in the morning when your body's super
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calm and still, and you're at the kind of the nadir, you're in the valley of your energy
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expenditure for the day. Your organs are as quiet as they're going to be. You take basal metabolic
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rate, you take how much people exercise, you take how much energy it takes to digest food,
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you add those up and there's kind of missing calories because people are burning more calories
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than those three components would suggest. You add those up, you don't get the same numbers you
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get when you really measure it as a real empirical measurement. It being total calories
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burned over 24 hours. And so people thought, well, there's this NEET stuff too. There's
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movement when we're not paying attention. And that's true. So we could add that in as well.
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And I would say there's other things as well that we don't always pay attention to that we need to
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think about as well, which is like the circadian fluctuations, the circadian rhythm of our energy
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expenditure, right? You're burning more energy in the middle of the day, especially when you're
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alert than you are at night while you're sleeping, right? So even without moving, just the act of being
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alert and awake and at the peak of your circadian metabolic cycle is going to be burning more energy
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than at your lowest point. So we can get into the weeds, you know, we can get into kind of the
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nuanced weeds about how the body spends energy, but you're right. We can break it down into those
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components as well. But I think the big takeaway, the majority, like you said, the majority of our
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calories burned throughout the day is this BMR, this basal metabolic rate. It's just when we're at rest,
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thinking, breathing, heartbeating, liver producing all the hormones that it does. That's where most
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of our energy is geared towards. Okay. That's right. So let's talk about how our body takes the food we
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eat and converts that into energy. So basically when we consume food, you can categorize the nutrients
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in that food into three broad categories. They're called macronutrients. We got protein, carbs,
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and fats and our body metabolizes these different macronutrients differently. Can you walk us
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through, you know, big picture? And we don't have to get into the Krebs cycle, but big picture, like
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what are the differences between how our body takes these different macronutrients and turn them into
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energy so we can power our bodies? Yeah, sure. So we can start with carbs. So carbs include starches,
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they include sugars. And no matter whether it's a complex carbohydrate, like you get from a potato,
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or if it's a simple sugar, like you get from the sugar in your coffee, your body in your digestive
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tract breaks those down into very simple sugars, things like glucose and fructose. Glucose is by
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far the major simple sugar. So that's why we talk about blood glucose levels because that glucose
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gets absorbed into your blood. And then really it only has a couple of places to go. It can go and
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get stored as glycogen, which is kind of a short-term savings account for glucose because the glucose is
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really just all about energy. It can get turned into fat if your glycogen stores are already full
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because glycogen, there's a limit to how much glycogen your muscles and liver can hold, or it
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can get burned as energy. And so that's what it's going to eventually end up happening is it's going
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to get burned as energy. But if you're not using it right now for energy, the glucose, you can store
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it as glycogen or fat. The fat that you eat will also get broken into the fatty acids and those get
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stored as fat or burned. And the proteins you eat get turned into tissues like muscle tissue. You're
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constantly cycling through muscle tissue because you break it down during the day and you build it back
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up at night. And your other tissues need protein as well. We're kind of protein robots walking around.
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We need a lot of protein to build our tissues. And then when proteins get degraded, when tissues break
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down, your body will break those down into amino acids and burn those as well. But the main energy
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supply for your body is the glucose and the fat. And protein is mostly a building block.
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And we can get into the weeds there. Like you say, there are, for example, there are sugars that
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help build your DNA. There are fats that help build your cell membrane. So things get used for different
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jobs, but those are the three big jobs. Gotcha. Okay. And so I think, okay, the big takeaway here is
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you literally are what you eat, right? When you eat carbs and fats, that stuff's in proteins,
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it's broken down and it's powering every part of your existence. And the idea is, okay, if you eat
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this stuff, you say you eat a pizza, use this example. If you eat a pizza, pizza, your body's
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going to process that, break it down. You might use it right away for energy. If it doesn't need
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that energy right away, if it's glucose or carbs, it's going to store it as glycogen. If the glycogen
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stores are too full, well, then the body's like, okay, well, we're going to save that energy for later.
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We're going to turn that into fat. We're saying with fat, you eat fat, you either use it right
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away to power your body. If your body doesn't need it then, then it will store it as fat around
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That's the basic idea. Okay. Okay. So now we have kind of this basic understanding of how
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metabolism works. Let's get into your research because like I said, it's counterintuitive what
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you found because I think a common idea out there that people have is that if you move your body
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around a lot, you're going to burn more calories than someone who moves less. And that's exactly why
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people, when they say, I'm going to start losing weight, what do they do? They sign up for the gym,
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But what you've done with your field research as an anthropologist, you went to a group of hunter
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gatherers in Africa called the Hasda. And you measured their daily caloric expenditure. And the
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Hasda, their hunter gatherers, they're moving around all the time. They have to move to eat,
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whether they're gathering tubers or hunting animals out in the wild. They've got to work a lot
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to get their food. And you figured, well, they probably burn a ton of calories because they're
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moving all the time. What did your research find?
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Yeah, that's right. So we did this project because humans evolved as hunter gatherers.
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So our species is Homo sapiens, right? So we're in this genus Homo. The genus Homo is older than us.
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It's two and a half million years old. And for the last two and a half million years,
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the entirety of the genus Homo's evolution, we've been hunting and gathering. And then our species,
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Homo sapiens, shows up about 300,000 years ago. And we're just one more hunter gatherer group
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in a hunting and gathering genus. And so if you want to understand anything about how our bodies
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evolved or what our bodies are built for, a hunting and gathering community, that's the best
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context you can have. Now, they're not living in the past. They're not trapped in
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amber or anything like that. They're as modern humans as you and I are. But because they've
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held on culturally to this hunting and gathering lifestyle, it allows you to ask, how do our
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bodies work in a hunting and gathering lifestyle? So it's one of the best windows you'll get
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into how our bodies were shaped for hunting and gathering. And like you say, they're incredibly
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physically active. We worked with a group called the Hadza in Northern Tanzania. They get more
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physical activity in a day than most Americans get in a week.
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And so going into it, we thought, well, gosh, we have to understand how many calories they're
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burning because obviously it's going to be a lot different than you and me.
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And so we went there. We stayed the first time I went there. I went for about two months
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living with them, measuring energy expenditures over the course of a week with this isotope
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tracking technique, which is a really, really good empirical objective measurement of calories
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burned per day. And you get it over about a week long period. So it's a really good look
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at daily energy expenditure. And yeah, we got back to the States with our samples because
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we use urine samples to track this stuff. We had to get them analyzed in a lab down at Baylor.
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And we got the numbers back and we're shocked because Hadza men and women were burning the
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same amount of energy every day as people in the US and Europe and other industrialized countries.
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There was no difference. I mean, in fact, Hadza men and women are burning less energy.
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Every day, fewer calories every day than men and women in the West. But once you account for body
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size, they tend to be a bit shorter. So once you account for body size, it's indistinguishable.
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You cannot distinguish daily energy expenditures between us and them. It's really, really remarkable.
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Okay. And just to be, I want to, I want to emphasize this point. Like they on average walk
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like five miles a day, I think it was like one at least. Yeah. That's the women, the men walk further.
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Yeah. Absolutely. And you know, Western like me, I don't, I'm lucky if I get my 10,000 steps in
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a day. Yeah. So that's a fun way to do it. The women get about 13,000 steps a day on average,
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you know, often with a kid on their back. Men get about 19,000 steps a day on average.
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All right. So what's going on there? How is it that they're able to burn the same amount of calories
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as us not so active Westerners? What's going on? Yeah. Yeah. Well, that was the big puzzle.
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And so we've been trying to figure that out for the last 10 years. Here's what we know. We know that
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there, there's nothing magic about the way that they're moving, right? So there we've measured the
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energy cost of, of their walking. We've taken a system out there that allows us to measure the
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energy cost to walk. And it's the same as you and me. So there's nothing special about their muscles
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or not more efficient that way. Instead, what seems to be happening is the energy that they spend on
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activity is being, rather than kind of adding on top of everything else and creating a higher
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total energy expenditure per day, the energy that they're spending on, on all that activity is
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taking away from other expenditures. So basically they're, they're reducing other expenditure and
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other aspects of their, of their bodies to make room for this really large amount of energy spent on
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daily physical activity. And like, where do you, have you been able to see where,
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you know, the body's taking away what's going on? Like what, where's, where's the body reducing
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caloric expenditure so we can, they can take into account that extra activity?
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Yeah. So this is, this has been the focus of research over the last few years.
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Here's what we know. And part of this is based on what we know from groups like the Hadza.
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And part of this is what we know from other people, like, for example, athletes in the U S and
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elsewhere who are also really physically active and, and in some times are easier to study because we can
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get them into labs here. Here's what we know. When you're really physically active, you have lower
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levels of baseline inflammation. So things like C-reactive protein and the other stuff that's,
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that is your immune system kind of overreacting all the time. There's high levels of inflammation
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that Westerners tend to have. It's lower in people who are really physically active. So that's your
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immune system, basically dialing it back, spending less energy. If you're really physically active,
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reproductive hormones, testosterone levels, estrogen levels in men and women, respectively,
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are lower in groups like the Hadza and in, in athletes as well. Um, endurance athletes as well.
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If you are a Hadza man or a Hadza woman, your, your reproductive hormone levels are going to be
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substantial, you know, maybe like 20% lower, 30% lower than an adult, your age. There's an age effect,
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of course, as well with reproductive hormones. So we're accounting for age with that.
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And that's your reproductive system spending a little bit less energy on, you know, uh, keeping
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its itself up. And that's, that's going to save energy. Now that doesn't mean I want to be really
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clear. That doesn't mean there's fertility issues or anything like that, or that they're any less
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manly than men, because they have slightly lower testosterone levels that not nothing like that,
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but just the reproductive system is just taking a little bit less energy per day and really physically
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active folks. And then the other big thing, and we don't have measurements of this with the
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Hadza, but we do it with other physically active groups and with athletes, stress levels
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and stress reaction, stress reactivity, right? So if I stress you out, I cost you on the street
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and, you know, give your heart a bump and in your epinephrine levels go up, your adrenaline levels
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go up, your cortisol levels go up. Or if I do that in the lab and I make you do mathematics
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in public, that's a really fun way to get people to get stressed out. Your heart rate will
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go up, your cortisol levels go up. But if you're an athlete, or if we think if you're
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someone like the Hadza, who's physically active all the time, that reaction will be not as sharp,
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not as big, and you'll go back to baseline faster. You'll spend less energy on that stress reaction
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than if you are a sedentary person who doesn't exercise a lot. So these are all the different
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various ways we think that the body's able to kind of take energy away from other tasks
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in ways that actually are really healthy for us. We can talk about that too.
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I guess to help people understand this, why this is going on, basically our body's
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regulation system for metabolism, it's all geared towards surviving and reproduction,
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right? And so, yeah, it makes sense. Like, you know, you talk about the reproductive hormones
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going down. Well, if you were facing extreme physical activity, extreme caloric expenditure,
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just to survive, right? To get food, your body's like, well, we're going to prioritize
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survival over reproduction a bit more. So we're going to adjust things. So, I mean,
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I guess that people just understand that your body's metabolizing energy to either
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to survive and reproduce, it's going to modify things to further those goals. I guess survival
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is the first goal and the reproduction is number two.
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Well, yeah, I mean, it depends. Some species that are short-lived, it's all about reproduction.
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They'll throw away the survival piece. Humans, because we're long-lived, we're evolved to be here
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for the long-term and to get through the tough times. Yeah, that's right. Well, in a bad time,
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we'll focus more on the survival piece. Our bodies will. But, you know, we see this kind of
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reproductive issue, reproductive effects in the Hadza. So a woman in a Hadza community, you know,
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they like big families, they don't use contraception typically, but a woman will still have a kid
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every, between two and three years, right? So that's without, you know, without any contraception.
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In the West, women who have a kid, you know, this year, even if that woman decides to breastfeed
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and is, you know, so she's nursing, if she doesn't use contraception, is likely to be pregnant again
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within a year, right? So it's much, the reproductive system is actually kind of, it's dialed back a little
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bit in these really physically active groups. And by the way, that's probably more, more healthy
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that most guidelines for things like pregnancy say, you should put more time between pregnancies,
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right? So, so that's one, you know, it's a, it's a good thing, but you can see the impact of how the
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energy is being spent. And so what you guys have found, what your research has found is that basically
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our bodies, all human bodies have this sort of constrained daily expenditures, like the kind of,
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there's a range kind of upper limit range of how many calories you can burn through a day.
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Yeah, that's right. So it's not just the HODs. I want to be clear about that. We've done,
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you know, if you're a scientist and you find this really interesting result,
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the first thing you assume is that you're wrong. So you got all the, you know, we've done all the
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work to try to make sure that that's a really strong state, a good result for the HODs. And it
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is, you can use different techniques, different approaches, you get the same answer. So the HODs
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data are solid, and then you want to replicate it. You want to make sure it's not just one
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society where you're seeing this or even one species. And so we've seen this in other human
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groups. Now we've looked at other like farming and hunter gatherer groups and mixed groups.
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You see the same thing, same daily energy expenditures as Westerners, industrialized
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communities, even though they're much more physically active. We see this across species. So,
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you know, we've done this study where we looked at different species of primates, monkeys and apes
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and lemurs and lorises in the monkeys in a zoo from the same number, number of calories every day
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as monkeys in the wild, right? You can do this in a laboratory setting. You can get mice, you can take
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out their running wheel away from them for a while and then give it back. And, you know, they're less
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active and they're more active and you don't see any effect on their daily energy expenditure.
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So this is a really robust thing. Our bodies and probably all, all mammal species, maybe even bird
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species too, seem to be built to, to really try to regulate how many calories we're burning every
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day. So in humans, what's the constrained daily expenditure? Like what's the range?
00:21:18.480
Well, it's going to be a function of your body size. Bigger people will spend more energy than
00:21:21.960
small people, but women burn about 2,400 kilocalories a day. I'm saying kilocalories
00:21:27.100
because we always say calories is actually not correct, but you can, you can just replace that with
00:21:31.780
capital C big calories if you want to, but women burn about 2,400 kilocalories a day.
00:21:37.060
Men burn about 3,000 kilocalories a day. And that can vary a little bit again with your
00:21:42.320
body size. That's the biggest factor, but lifestyle has a really small effect on it.
00:21:46.340
All right. So this is across about 3,000 calories, whether you're a Hadza or some guy in New York,
00:21:51.500
your body's probably burning about three. And this, this is like total. So this includes,
00:21:55.280
this is like a BMR. So that resting based on metabolic rate and like your activity.
00:21:59.720
Yep. It includes that. It includes the energy to digest your food. It includes whatever exercise
00:22:05.380
you did. It includes, you know, taking that walk to go get a coffee. It includes the stress reaction
00:22:11.020
from your boss throwing extra work at you at five o'clock, all that stuff.
00:22:15.580
Okay. So the implication of this finding is that relying solely on exercise to lose weight
00:22:21.400
is probably not an effective strategy because you know, your body, because you exercise to burn more
00:22:26.680
calories than you're consuming. Yeah. But you're basically, we've discovered our body's going to
00:22:30.660
figure out a way to compensate for the increased physical activity so that you stay inside your
00:22:36.200
constrained daily expenditure. Yeah. There's, there's two reasons that exercise ends up being
00:22:40.300
a poor tool for weight loss. One is what we've been talking about. Your body will adjust and you
00:22:45.080
know, you're adding, you think you're adding 300 calorie kilocalories a day to your daily routine
00:22:50.460
of exercise, but you're not really because that 300 kilocalories of exercise is at least partially
00:22:55.820
being eaten up by adjustments, other places. The other thing is that even if you are able to
00:23:01.920
manage to pump your energy expenditure up a bit with exercise, especially in the short term,
00:23:07.200
because it takes a while for the body to adjust, you're going to eat those gains because your body
00:23:11.840
is also part of the system is your body's very well evolved to match energy intake with energy
00:23:19.180
expenditure. And that also happens below our conscious thought. So if you are able to increase
00:23:24.160
your metabolic rate by a bit, you're just going to eat those gains and you're going to end up
00:23:28.140
right back where you are, where your energy intake matches your energy expenditure and you're not
00:23:32.840
changing your weight at all. All right. So I'm sure people are listening to this like, well,
00:23:35.480
this is depressing, but we're going to talk about why exercise is still important.
00:23:39.280
We're going to take a quick break for your word from our sponsors.
00:23:43.380
And now back to the show. Okay. So people might hear this and think, okay, if I want to lose weight,
00:23:47.900
then exercise doesn't do anything for me. What I need to do is reduce the number of calories I take in
00:23:53.020
by a lot to lose weight, but that doesn't work either and can even backfire sometimes. So what
00:23:59.480
happens when we significantly reduce our caloric intake? Yeah. If you go on a crash diet, you know,
00:24:05.140
really like cut the calories in half kind of thing, then you're, this is another evolved
00:24:10.940
survival response. Your body says, oh my gosh, we're, we're starving. There's no food in the world
00:24:16.500
and we got to get through this lean period. And so what it'll do is without your being aware of it,
00:24:23.640
it will reduce your metabolic rate. So all those systems that you're not aware of,
00:24:28.340
your body can take the foot off the gas and spend less energy on those. And all of a sudden,
00:24:33.620
you know, you aren't burning as many calories as you were before. And not only do you feel
00:24:37.940
miserable because you've, you've, you're starving yourself, but you're actually making a, your body
00:24:42.980
is actually trying to frustrate those weight loss attempts, the weight loss effort, because it is
00:24:48.140
reducing the energy expenditure that you had before. So it's actually, you know, that, that,
00:24:51.900
that difference between the energy you're taking in and the energy you're burning gets smaller
00:24:54.760
because your body's saying, oh my gosh, we're starving, turn the energy down.
00:25:00.080
And so that we've seen this with, with the biggest losers contestants, right? Like they,
00:25:04.340
they go like, they're losing a hundred, like, I think it was like 152, like basically like a human,
00:25:10.120
they lose a human off of their body, a full grown human. And then you do the follow of like,
00:25:14.720
well, how do they do afterwards? And I think most of them gain the weight back.
00:25:19.060
They almost all do. And that's really, it's sad because of how much effort that, you know,
00:25:23.040
they put into it and how much it meant to them. But it's also kind of predictable because your body
00:25:27.880
doesn't want to change weight, right? For, you know, there have been, you know,
00:25:32.920
vertebrates were the group of animals called vertebrates. We've been around for half a billion
00:25:37.160
years. And for almost all that time, probably all of it, losing weight's been a really bad thing,
00:25:43.640
right? You're losing weight, you're on your way to dying. And so there are all these evolved
00:25:49.040
mechanisms not to lose weight, which is why it's actually the most important thing you can do for
00:25:53.420
your health is to try to not get overweight in the first place. And that's, you know, that gets us
00:25:57.520
into discussions about how we think about how we take care of our kids and how we take care of
00:26:01.120
ourselves, especially in our early, you know, in our early years. But yeah, it's really hard to
00:26:05.940
change once you do, once you're overweight, the best thing you can do is, you know, if you're
00:26:10.880
looking at behavioral strategies is to try to change your diet. But like you say, if you go too fast,
00:26:16.500
too hard and too fast, too soon, then that can backfire because your body responds to that by,
00:26:22.080
again, reducing energy expenditure and frustrating that weight loss.
00:26:26.060
Right. So yeah, the metabolism, you can't outsmart the metabolism. Like there's no,
00:26:32.340
Yeah. One of the biggest frustrations I have when I look at like online,
00:26:34.600
you know, self-help, here's how you're going to take charge of your metabolism and boost your
00:26:38.880
metabolism or whatever. All of this stuff, it all makes people think that they're in charge of
00:26:44.400
their metabolism, right? Which is completely not the case. Your metabolism is working behind the
00:26:49.680
scenes. It's smarter than you. And it, you know, it, it adjusts to you. You can't really
00:26:55.740
push it around in a way it'll, it'll manipulate things behind the scenes in ways that, that are
00:27:02.200
going to frustrate what you're trying to do now. And I hope we're going to talk about this. You
00:27:05.400
should still exercise. Absolutely. And if you do want to try to lose weight with diet, there's
00:27:09.920
some strategies you can take. But I think, you know, this idea that we're in the driver's seat,
00:27:15.820
you know, revving our engines, our metabolic engines in a sort of really simplistic way. And that's
00:27:19.280
how we burn calories. I wish we could move away from that because it's just not the science.
00:27:23.480
Right. So you can't speed up your metabolism. Like that's, yeah, it's really hard to do. And
00:27:27.360
basically, yeah, you can't do it. Okay. So let's talk about this. So while exercise can't be the
00:27:31.440
sole driver of weight loss, you make it very clear, you devote a whole chapter to this, like
00:27:35.200
that doesn't mean you shouldn't exercise. And you actually make the case that because of humans'
00:27:40.520
unique metabolism, maybe we can talk about how it differs from the apes because of our unique
00:27:44.940
metabolism, we actually, it's really, really important for us to move a lot.
00:27:50.280
Yeah. Well, so, you know, like I said, we've been evolving as hunter-gatherers for two and
00:27:53.580
a half million years and hunting and gathering takes a lot of work, you know? And so our bodies
00:27:59.440
are actually evolved to expect and require a lot of physical activity every day. It's what our
00:28:07.120
organ, you know, as a, as a evolved organism, it's what we're evolved to do. And if we don't do it,
00:28:13.440
we get sick. And so, you know, yeah, getting all those steps every day is really important.
00:28:18.900
And ape, apes are lazy, right? I mean, I've done, I've done field work with apes. I've worked with
00:28:22.800
apes in zoos. They're impressively lazy. Getting 5,000 steps a day, maybe, you know, is kind of a
00:28:29.900
typical day for, for an ape, even if you count up the climbing and all that stuff. And so, and they're
00:28:34.540
just fine like that. They, they don't get sick from being like that. In fact, a chimpanzee in a zoo
00:28:38.380
probably has less than 10% body fat. That's, that's a typical, that'd be typical for a
00:28:43.020
chimpanzee in a zoo, even though they're just sitting around. And so we, we can't do that.
00:28:47.260
If we, if we act, you know, on our ape-like impulses just to be lazy all day, yeah, we get real sick.
00:28:53.620
Yeah. That, that, that was really interesting to me is that apes in captivity don't really get fat.
00:28:58.180
Like when they eat more food, instead of, you know, turning that into body fat, apes just turning
00:29:02.320
that into lean tissue. Yeah. Isn't that crazy? Humans are, it's another evolved piece of our,
00:29:07.460
you know, of our physiology. We are evolved to put on fat really, really easily. And it probably
00:29:13.160
goes hand in hand with having a faster metabolism. So we've actually evolved a faster metabolism
00:29:17.900
than apes have that allows us to have things like these big brains that we are so energetically
00:29:23.260
expensive. And we have big fat babies more, and we have them more often than apes do. That takes a
00:29:28.340
lot of energy. We are physically more active than apes. So all of this is like, so we're a high energy
00:29:32.620
ape, you know, and as a kind of a backup plan, we've also evolved this propensity to put on fat,
00:29:38.820
because if you're, you're always burning a high level of energy, you have a high metabolic rate
00:29:44.140
that you can't kind of turn down. You can't adjust much at all. As we've been talking about,
00:29:48.540
you need to have a backup in case, you know, you have periods where there's not much food
00:29:52.620
and that's where our, our body fat comes in. Right. So yeah. Okay. Okay. Just to make sure I'm
00:29:58.480
getting this right. So apes, they don't have to move around a lot to get their food. Right. So
00:30:02.140
they have a slow metabolism and there'd be no reason for them to put on body fat really, because
00:30:07.760
they would never, they would probably wouldn't be long periods of time where they wouldn't go
00:30:11.260
without food. It's like, well, I'll just grab this leaf here. Humans, we have to hunt and gather
00:30:16.000
to gather our foods. That requires a lot of energy. Yeah. And so we have to, if there's instances
00:30:20.760
where we don't have a lot of food available, our body's like, well, we need to have, we need to store
00:30:25.380
body fat in case that ever happens so that we have the energy to walk and find tubers and gazelle
00:30:31.180
again. Yeah. And reproduce and do all those things that, that we're built to do. Absolutely.
00:30:35.760
Okay. So we have to move a lock. So our body uses a lot of energy. You also highlight research that
00:30:40.200
exercise, while it isn't, isn't useful to lose weight, it's really important in maintaining weight
00:30:45.420
loss. What's going on there? Yeah, that's a really interesting piece of this. So, you know,
00:30:49.640
if you go on an exercise program tomorrow, yeah, you might lose a couple pounds over the course of a
00:30:55.060
year, but that's not the big benefit of it. Big benefit is how it kind of makes a lot of our
00:31:00.500
systems more healthy. And if you, you know, if you're able to lose the weight with, with usually
00:31:06.220
with diet as the big intervention, that exercise helps you keep it off. And we don't entirely know
00:31:12.040
why. What we think is happening is that the exercise, when you exercise, your muscles send all
00:31:19.860
these signals to your body, all these hormones and paracrines, all these things. So your body
00:31:25.360
knows you're exercising. It affects every part of your body. And one of the things we think it helps
00:31:31.520
do is regulate how hungry and how full we feel. So how much we eat. And so, you know, the kind of
00:31:39.620
exercise has this effect of keeping our hunger and fullness better regulated. So we don't overeat.
00:31:47.840
Once we've lost the weight, if you exercise, it helps you keep at that weight and not overeat and
00:31:53.940
gain all that weight back. So, yeah, I think when people, okay, I want to, there's some interesting
00:31:58.960
things going on here because our metabolism is, again, is weird. When we exercise more,
00:32:02.220
we're going to eat more because we need more energy. Right. But I think what you're saying here
00:32:06.860
is that when you exercise, like there's a better connection between the calories you need and like
00:32:12.440
your hunger levels. Right. So it's like, yeah, that's right. Yeah, that's right. And once,
00:32:15.820
once you've lost the weight, the energy that you need is actually less, right? Because you've lost
00:32:20.620
all that weight. And so if your body was just trying to match how much you need and how much
00:32:25.960
you're taking in, you'll match that at that lower level and maintain the weight better. That's what
00:32:31.780
we think is going on. It's actually not entirely well understood why exercise is such a good tool
00:32:36.080
for keeping weight off, but it absolutely is. That's what all the data show.
00:32:39.780
Okay. So overall exercise, it's going to help you lose a little weight,
00:32:42.740
but it's really useful in helping you keep the weight off and maintaining your weight loss.
00:32:47.980
And it's probably because it helps match your appetite to your actual caloric needs. It's
00:32:53.640
helping control those hunger signals. And something that's interesting with this research is that they
00:32:59.160
found that sedentary people, like people who don't move hardly at all, they actually eat more than those
00:33:04.840
who are active. And it's probably because their bodies have somehow become out of touch with how much
00:33:10.720
food they actually need. And then something else, we talked about Biggest Loser contestants.
00:33:15.400
Something else that's interesting with the research there is that with all the contestants,
00:33:19.080
their metabolisms dropped after the show, and then it stayed low long-term. But among those who
00:33:25.260
exercised, even though their metabolisms were low as well, they actually did the best in keeping the
00:33:31.000
weight off. And again, it's probably because of the way exercise regulates appetite.
00:33:36.040
So yeah, exercise plays a big role in weight maintenance.
00:33:40.960
The other thing that it's doing, all of the other adjustments it's doing, keeping your
00:33:44.920
inflammation levels down, your reproductive hormones in a healthier place, your stress reactivity down,
00:33:49.600
that is going to add years to your life. Those are all ways to avoid heart disease,
00:33:55.180
avoid diabetes. The things that we're most likely to die from is by exercise. So thinking about exercise
00:34:01.640
as a weight loss tool kind of misses the point. It's actually really good for all this other stuff
00:34:05.960
that's going to keep you healthy and active and add not just years to your life, but healthy,
00:34:12.620
Well, let's talk about diet because I think that's the way we can lose weight, right?
00:34:16.760
Just reducing calorie intake. But then there's people who have created diets based on how our
00:34:22.560
body metabolizes different macronutrients. And I think the most popular one is a low-carb,
00:34:27.300
high-fat diet. And I think the big idea is Gary Taubes' idea is like, well, the reason why you
00:34:32.200
get fat is insulin. And when you eat carbs, insulin levels spike, and it drives the storage of carbs or
00:34:39.800
fat as body fat. So you cut the carbs, you reduce the insulin, you're going to lose weight.
00:34:45.800
What does your research reveal about diet and weight loss based on a macronutrient?
00:34:52.160
Yeah, the carb idea. It's a beautiful idea. It just doesn't fit the evidence, unfortunately.
00:34:59.320
So first of all, we can say a group like the Hadza, and there are lots of them still that are
00:35:05.440
farming and hunting and gathering and doing that kind of stuff. They eat a lot of carbs. In fact,
00:35:11.280
they eat more carbs as part of their diet than people in the US do. So if it were all about carbs,
00:35:18.180
then folks like the Hadza should be incredibly obese. But of course, they're not. They're quite
00:35:23.300
healthy weight throughout their whole lives, and they don't ever gain weight in their middle and
00:35:28.020
older age. They're just fine. And so if it were really just about carbs, then groups that eat a
00:35:32.640
lot of carbs ought to be overweight. They're not. Secondly, when you do the controlled laboratory studies
00:35:40.640
and you put people on low-carb diets versus on low-fat diets, you don't see any difference in
00:35:47.660
weight loss outcomes. In fact, depending on the study, sometimes you see people do a little bit
00:35:51.560
better on low-fat. But the main outcome is that you just don't see any difference at all.
00:35:57.460
If you cut calories by cutting carbs or you cut the calories by cutting fats, you get the same
00:36:01.240
outcomes. And the third is, if you do a study where you take people and you randomly assign them
00:36:07.980
to a low-fat diet or low-carb diet, this has been done a few times now, there's no difference in
00:36:16.060
outcomes. People, again, lose weight just as easily, just as well on low-fat as they do on low-carb
00:36:22.840
diets. And so there's just really no... The carbohydrate insulin model of obesity, which is
00:36:29.140
the Gary Taubes idea, it's been tested in a lot of different ways. And it's a beautiful idea. It's very
00:36:34.080
elegant. It just doesn't work. It just doesn't fit the data. Now, low-carb diets work for a lot
00:36:39.260
of people. That's a different question, right? The question is, why are they working and how do
00:36:44.380
they work? And the answer is, basically, you're cutting calories. But that doesn't mean that the
00:36:49.200
mechanism that's been proposed, this insulin-based mechanism, is really what it's all about because
00:36:52.640
that just doesn't bear out. All right. So again, you can't trick your body, your metabolism.
00:36:58.080
Well, no, I think this is a different thing about tricking, right?
00:36:59.940
So the counter-argument from the folks like Gary Taubes would be like, oh, well, you're saying
00:37:07.020
all calories are the same. You're saying that it doesn't matter what you eat. Is that what you're
00:37:10.240
saying? And the answer is, well, no, no, we're not saying 100 kilocalories of broccoli is going to
00:37:17.780
affect us differently and feel different than 100 kilocalories of potato chips, right? So in both
00:37:23.940
those cases, those are very carb-heavy foods. And so the kinds of foods you eat matter, but all the
00:37:31.160
evidence says that the way that you feel full on fewer calories, which is really the goal to lose
00:37:35.740
weight with diet, is that we have to think about the way that those calories affect our brains,
00:37:41.360
right? So we talked about how your brain is really well adapted to match the calories in and the
00:37:45.280
calories out, to match our fullness and hunger to our weight. The way that you kind of push that
00:37:52.540
system to lose weight without feeling miserable is to find foods that make you feel full on fewer
00:37:59.500
calories. So things like higher fiber foods can help, higher protein foods can help. That's where
00:38:04.780
low-carb diets come in. By the way, you take a whole macronutrient group out and you give yourself
00:38:10.160
foods that you typically have a lot of protein in them and you feel better. You feel full on fewer
00:38:14.380
calories. That's why low calories work for some people. Yeah. So that's what we're talking about
00:38:18.460
here. So we're not saying that foods don't have different effects, that kind of stuff. Of course
00:38:23.660
they do. But do all diets work through the insulin pathway or do they work through manipulating the
00:38:29.780
way our bodies feel, our brains feel? That seems to be the more likely mechanism.
00:38:34.680
Yeah. We had Steven Guine on the podcast a while back ago and he talked about this,
00:38:37.980
right? Like our brain, how it feels about our food that we're eating. And one of the interesting
00:38:43.600
takeaways I got from him was one thing you can do is just eat like less palatable food because
00:38:47.960
like palatable food, like you just want to eat a lot of it, right? Like we're talking about Doritos
00:38:50.820
and cheeseburgers. Like, oh, I just want to keep, but it's like, if you look at the diet of like the
00:38:55.360
Hadza, it's like the most boring thing. There's no spices. It's just like, well, I'm going to eat a
00:38:59.800
tuber. It's kind of burnt and like some zebra. Yeah. That's just gross. And so it's usually like,
00:39:04.540
well, I'll eat enough to get the energy I need to do what I got to do, but I'm not going to.
00:39:09.100
So one takeaway is just like eat a, instead of eating a potato chip, eat a baked potato. Yeah, that's right.
00:39:13.600
I mean, there's actually a great, you know, set of, most of it's anecdotal because nobody,
00:39:18.420
no real nutritionist would ever recommend this diet. And I'm not to be clear, but there's great
00:39:22.980
anecdotal evidence of people who just eat potatoes and lose, you know, lots of weight that way, you
00:39:28.560
know, hundreds of pounds sometimes, because if all you eat is potatoes, guess what? You are sick of
00:39:33.180
potatoes well before you have overeaten your calories that day. And so that's one way to do it
00:39:39.960
for sure. And I think that's what low carb is doing as well, right? You take a whole
00:39:43.320
class of foods, you know, off the menu and you know, how much steak can you eat? You know,
00:39:48.940
how much spinach can you eat? You're just, you're going to feel full before you overconsume.
00:39:54.440
And, and that's, that's a great way to go for some people that works really well,
00:39:57.820
but it's not the only way to go. And it's not because of this kind of carbohydrate insulin
00:40:02.020
magic. I think it's much more about our brains than that.
00:40:06.960
So I think another common idea people have about metabolism. So, okay. I guess, okay.
00:40:11.260
We kind of debunked a lot of things, right? Exercise isn't going to do much for you to lose
00:40:15.520
weight diet, you know, basing a diet on a macronutrient, probably not, it's not going
00:40:20.640
to do anything for you. I think another popular idea people have about metabolism is as you
00:40:24.900
get older, it slows down. That's why people when they're 50 or 60, you got the belly.
00:40:33.540
You know, man, I'm in my forties and I was really sure that one was true. And then we just
00:40:38.160
recently did this big study. We took measurements from 6,400 and some people. And those are people
00:40:44.640
from, you know, people who had just been born eight days old up to folks who were in their
00:40:48.400
nineties. And what we did is we were able to use that big, big data set to measure how many calories
00:40:54.320
people burn every, over the course of a day and ask how that changes over a lifespan.
00:41:00.560
What we found was that your metabolism is really steady and stable between about 20 years old
00:41:08.960
and about 60. And so there's no slowdown in your thirties and forties that we were able to detect at
00:41:15.700
all. Yeah, that turns out to be another one of these myths. So that, you know, that's not to say
00:41:21.280
that it feels the same to be 44 as it does to be 24. I can attest to that, but it's not metabolism.
00:41:28.260
It's not the energy burning that's changing. It's, it's something else. It's about, you know,
00:41:31.620
stress levels or hormone levels, that kind of thing. Uh, so, but it does start slowing down
00:41:36.100
after 60 at 60. Yeah. And that's really interesting because 60 is also kind of that inflection point
00:41:41.980
where people start to, you know, people get into their sixties, seventies, eighties. That's when you
00:41:46.040
see your risk of different, you know, different diseases, pick up heart disease, Alzheimer's disease,
00:41:53.260
other diseases that we associate with aging. That's, those are when those really start to
00:41:58.620
kick in is after 60. And we're seeing your metabolic rate decline too. What does that mean?
00:42:03.400
That your cells are slowing down, right? That's what your metabolic rate, we started off by talking
00:42:07.200
about what metabolism is. It's all your cells at work. When we see that metabolism is starting to
00:42:11.840
slow down, well, that's telling us our cells are doing less work and man, we would love to know
00:42:18.100
exactly what's happening there. What's, what's changing that is, you know, is either promoting
00:42:26.420
or just kind of signaling and telling us about these changes in how our cells work that seem
00:42:31.400
to be related to the disease risk that we see picking up there. Because maybe, you know, maybe
00:42:35.680
we could find a way to keep our cells burning more energy and keep them at a younger state.
00:42:41.340
Maybe that would be protective against disease. I don't know, but it's a, yeah, something we need
00:42:45.940
to look into next is figuring out exactly why that, why that decline happens. And is that telling us
00:42:50.360
about healthy aging? I suspect it is, but we're going to have to have more work to figure that out.
00:42:55.860
Well, one idea that crossed my mind when you told me that at 60, it starts going down. That would
00:42:59.760
make sense if we understand that metabolism is about survival and reproduction. If you're over 60,
00:43:06.380
especially for women, like that's reproductions out off the table, like your body doesn't need
00:43:12.600
Yeah. So that's interesting, right? Because menopause typically happens when women are in
00:43:17.140
their forties, late forties. So actually from an evolutionary perspective, that last 15 years,
00:43:24.400
if we go to 60, let's say, that's kind of hard to explain. And what that seems to be about is that
00:43:31.060
the elders in our communities, and this is true in the Hadza, and this is also true here in the States,
00:43:35.680
and it's true, you know, historically and across cultures. Folks who are in their later middle age
00:43:41.220
are doing a lot of work and helping out their own kids and helping out the next generation.
00:43:47.180
And that seems to be really important. So we have this evolved strategy to share and to help.
00:43:54.020
It's one thing you cannot escape when you go to work with a Hadza. They're always sharing,
00:43:58.380
they're always helping each other out. And it's not just being nice, it is baked in to being a human,
00:44:03.500
right? And I love that about kind of the way the doors that this kind of metabolism work opens up,
00:44:08.740
you're like, oh my gosh, hunting and gathering, right? Like, it's not just one or the other,
00:44:13.480
you have to do it together. And that comes out of every celebration you've ever had, I bet,
00:44:18.660
involves hanging out with other people and sharing stuff, sharing food, sharing birthday cake,
00:44:22.740
right? That's what's been so hard about all the social distancing with COVID is we're built to be
00:44:27.220
social and together and sharing. Anyway, so getting up to 60 actually gets you past
00:44:33.640
your reproductive years for most of us. And that makes sense because again, it's really,
00:44:38.900
we need to work together. Maybe at 60 is around the time that most folks in hunting, gathering
00:44:45.120
communities, mortality rates kind of kick in at a higher rate there. And maybe that's kind of what
00:44:50.420
we're evolved to get to at least 60. And then the rest of that time you're in the bonus,
00:44:55.060
if you're in a hunting and gathering group, that would fit the mortality data all right.
00:44:59.540
So that's an interesting idea. But I do think it's clearly, it's an evolved piece of our
00:45:03.720
physiology. It's not something we decide to do is just slow down at 60. Our cells are built to start
00:45:07.780
doing that. All right. So what's a person supposed to do with this information, right? If someone's
00:45:11.780
listening to this and they think, well, I need to lose some weight, how should this research guide
00:45:14.980
their approach to losing weight? Yeah. Well, I think that a couple of things, you got to start
00:45:19.720
thinking about diet and exercise as two different tools, two different jobs, right?
00:45:24.280
Diet is your best tool for weight loss. Exercise is your best tool for staying healthy, especially
00:45:30.900
as you age. And there's some crossover there, but those are the main strengths of those two
00:45:36.040
approaches. For diet, if you want to lose weight, focus on foods that make you feel full
00:45:42.020
with fewer calories. And so we know what that looks like. I don't study diet per se, but lots of
00:45:49.400
people do. And if you look at that literature, people like Kevin Hall have shown stay away from
00:45:54.080
processed foods, the ultra processed foods, the Doritos, right? The sugary beverages, not because
00:46:00.420
of a carb or a fat or whatever, but the whole package is built, literally built, engineered
00:46:05.900
to make you overeat, right? They want you to overconsume. So whole foods, if you can do it,
00:46:12.640
and foods that are high in fiber or high in protein tend to make you feel full on less.
00:46:17.860
And the other thing I hear a lot about from people who are dietitians and work with people with
00:46:21.860
obesity is try to find the parts of your day that you're eating and you're not even hungry,
00:46:27.360
right? I mean, I know that, for example, when I get home from work, I get the kids in bed
00:46:32.400
and I finally have a little bit of time to breathe. I'll tell you what I do. I sit down on the couch,
00:46:41.120
catch them on work emails or watch TV or something like that, read a book, and I have a beer.
00:46:45.940
Now, I don't need that beer. And if I was trying to lose weight, that'd be one of the first places
00:46:52.260
I'd go is I would cut that beer out because I'm not hungry. I'm not even thirsty. If I was thirsty,
00:46:57.240
I could have some water, right? You know what I mean? But that's just calories that I'm just
00:47:00.520
doing out of habit that don't have any nutritional impact on me at all other than the calories.
00:47:06.320
So that's the focus you got to take if you want to lose weight.
00:47:09.080
And no extreme calorie cutting because that was just...
00:47:11.540
No, I think that's a mistake. I think cutting your calorie intake by a half,
00:47:15.520
for example, or by a third, yeah, you'll see some effects faster, I suppose, maybe,
00:47:22.960
but you'll also really mess up your metabolism. Your metabolism will slow down. Your body will freak
00:47:26.920
out, go into starvation mode, reduce your expenditure. And there's no way to go. It's
00:47:32.020
also unsustainable, right? You will feel hungry. You'll feel miserable. And those feelings will win
00:47:39.680
out. And you'll go back to your old ways. You'll think, oh, gosh, it didn't work. Well,
00:47:44.280
it didn't work because, in part, because it wasn't sustainable to begin with.
00:47:49.100
Well, Herman, this has been a great conversation. Is there someplace people can go to learn more
00:47:53.440
Well, yeah. I hope they'll check out the book. You can get that anywhere you buy books,
00:47:56.440
your local bookstore or places like Amazon. You can check us out here at Duke University.
00:48:01.240
I'm on the... We've got a website here for the lab. You can find out what research we're into
00:48:04.580
right now. And I'm on Twitter. I'm on social media generally, but Twitter is where I'm most
00:48:11.220
Fantastic. Well, Herman Ponser, thanks for your time. It's been a pleasure.
00:48:15.520
My guest here is Dr. Herman Ponser. He's the author of the book, Burn. It's available
00:48:18.800
on Amazon.com and bookstores everywhere. You can find more information about his work at
00:48:22.040
our show notes at awim.is slash burn, where you find links to resources where you delve deeper
00:48:34.060
Well, that wraps up another edition of the AOM podcast. Make sure to check out our website
00:48:37.740
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00:48:41.400
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00:49:07.020
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