We all know the basics of losing weight: don’t consume more calories than your body needs. And yet many of us still overeat anyway, sometimes continually, sometimes to the point where it leads to obesity, diabetes, and a significantly lower quality of life. Why does our behavior betray our intentions to be lean and healthy?
My guest today argues that the answer lies in the ancient instincts of our brains that no longer fit the environment of the modern world. His name is Stephan Guyenet, and he’s a neuroscientist, obesity researcher, and the author of The Hungry Brain: Outsmarting the Instincts That Make Us Overeat. We begin our conversation with what’s changed in our country to turn obesity into an epidemic, and why Americans started gaining more weight in the 1970s. We then dive into exactly how the reward system in our brains leads us to eat more than we need to, how modern manufactured foods like Doritos hijack this reward system, and the factors that ramp up our cravings, including the buffet effect. We then explain how to push back on the desire to overeat, including reevaluating the assumption that all the food you consume needs to be delicious. From there we turn to the role that the hormone leptin plays in appetite regulation, how it can make it hard to keep the weight you lose from coming back, and the best techniques to manage this countervailing force. We end our conversation with the role stress and sleep play in weight gain.
If reading this in an email, click the title of the post to listen to the show.
- Why have obesity rates been rising for the last few decades?
- The insidious nature of between-meal eating
- Why does our brain want us to eat more than we need?
- The unique human need for salt
- What does dopamine really do?
- Why chocolate is the perfect food for our palette
- What role does variety play in overeating?
- The effort barrier and the insane availability of calorie-dense, delicious foods
- How to make overeating harder and healthy eating easier
- Does your food have to be delicious every time?
- What is leptin? What role does it play in our desire to eat?
- How to change your food environment
- The role of sleep in our eating habits
- How does stress affect our eating?
Resources/People/Articles Mentioned in Podcast
- How to Eat What You Want and Still Lose Weight
- How to Lose Weight, and Keep It Off Forever
- Everything You Need to Know About Diet and Fat Loss
- A Primer on Flexible Dieting
- Why Carbs Don’t Make You Fat
- The Advantages of a High-Carb/Low-Fat Diet
- How to Hack the Habit Loop
- Your Life Explained Through Dopamine
- Taking Control of Your Dopamine
- Diet and Nutrition Advice From the Doctor of Gains
- Your Grandpa’s Diet Plan
- 22 Ways to Get a Better Night’s Sleep
- What Every Man Should Know About Sleep
- How to Manage Stress
- How to Stress Proof Your Body and Brain
Connect With Stephan
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Read the Transcript
Brett McKay: Brett McKay here, and welcome to another edition of The Art of Manliness Podcast. We all know the basics of losing weight: Don’t consume more calories than your body needs. And yet, many of us still overeat anyway, sometimes continually, sometimes to the point where it leads to obesity, diabetes and a significantly lower quality of life. Why does our behavior betray our intentions to be lean and healthy? My guest today argues that the answer lies in the ancient instincts of our brains that no longer fit the environment of the modern world. His name is Stephan Guyenet. He’s a neuroscientist, obesity researcher, and the author of ‘The Hungry Brain: Outsmarting the Instincts that Make us Overeat’.
We begin our conversation with what’s changed in our country to turn obesity into an epidemic, and why Americans started to gain more weight in the 1970s. We then dive into exactly how the reward system of our brain leads us to eat more than what we need to, how modern manufacturer foods, like Doritos, one of my favorites, hijack this reward system, and the factors that ramp up our cravings, including the buffet effect. Stephan then explains how to push back on this desire to overeat, including re-evaluating the assumption that all your food you consume has to be tasty and delicious. From there, we turn to the role that the hormone leptin plays in appetite regulation, how it can make it hard to keep the weight you lose from coming back, and the best techniques to manage this countervailing force. We end the conversation with the role stress and sleep play in weight gain. After the show is over, check out our show notes at aom.is/hungrybrain.
Alright. Stephan Guyenet, welcome to the show.
Stephan Guyenet: Thanks for having me on, Brett.
Brett McKay: Alright. So you are a neuroscientist who studies the central role the brain plays in regulating hunger, and how appetite leads to overeating and weight gain. But before we get to those specific dynamics, let’s take a big picture view of what’s called the obesity epidemic. And I think, in the book, you said that we’re at something like 30% to 40% of Americans are obese or overweight today?
Stephan Guyenet: 42% is the latest figures.
Brett McKay: And I mean, so what… When did that… It wasn’t always like that. If you highlight all this research going back to the early 20th centuries, where it was really low, what were the numbers back then?
Stephan Guyenet: Yeah, that’s correct. It’s been rising over a long period of time. So if we go back… So, the best data that we have go back to the early 1960s. Those are from large-scale surveys conducted by the US Centers for Disease Control, and before that, the data gets increasingly sparse. But we do have data going back to the late 1800s, early 1900s, that paint a very different picture than what we’re seeing today. So, there was a survey conducted among white male Civil War veterans, who were middle-aged at the time, in 1890 and 1900, and what they found at that time is that fewer than one out of 17 of those middle-aged white men had obesity. Whereas, today, if we looked in middle-aged white men, it would be something almost like 50%. And so, there’s been a dramatic increase in the prevalence of obesity over time. And what we see is that that has happened very gradually, over a very long period of time, but it’s accelerated, particularly, between 1970 and 1980. So, between 1970 and 1980, we see a kind of sharp uptick in the prevalence of obesity, and that is what we call the obesity epidemic.
Brett McKay: And so, what’s going on? What are the things that have changed, starting in the 1970s, that caused this sharp uptick?
Stephan Guyenet: Yeah. So it’s impossible to say with complete certainty, because we’re looking retrospectively, and a lot of things have changed, and we’re trying to figure out what is important and what’s not. That said, I think we have some pretty good guesses, and the first place to start is that our calorie intake has increased quite substantially over that period of time. So, compared to the 70s, today, we eat roughly 218 calories per day more than we did. And it’s actually… That’s a very simplified picture, because what’s really happened is that some people are eating 400 calories more, some people are not eating any extra calories, and that’s explaining the divergence in weight that we’re seeing between individuals over that time period, ’cause what you see… If you’re looking at the bell curve distribution of weight, what you see is it’s flattened out a lot. So, in other words, it used to be that most people were clustered around a leaner distribution, and now we see there’s this huge tail where you have 9% of Americans now have what would be called extreme obesity, body mass index over 40. So these are the people who really are at very high risk of health impairments, and being the folks that you see in motorized wheelchairs, and that sort of thing.
And so, it hasn’t hit everyone the same. It’s really been this flattening out of the distribution over time. And yeah, so the question is, what explains that? Why did we start eating more calories? And I think the answer is that we’ve seen profound changes in how we interact with food, over time, in this country. What we see over a long period of time, but particularly accelerating during that time, is that we’ve increasingly outsourced food preparation to professionals. So, instead of cooking food at home, ourselves, we are now buying industrially-prepared food, we are now eating out a lot more at restaurants. We’re essentially outsourcing our food prep to people who have kind of different abilities and different incentive structures in how they prepare that food. And it’s also very, very convenient, which I think is important. And one of the things that… One of the ways in which that has expressed itself is between-meal eating occasions. So what we see is that that increase in calorie intake, most of that can be explained by the fact that we’re eating more between meals. So we’re snacking more, we’re eating… We’re drinking more sweetened beverages between meals than we used to. So, overall, I think this paints a picture of really profound changes in how we’re interacting with food in this country, in terms of how food is prepared, how we’re purchasing it, and how it’s distributed throughout our day.
One other thing that I’ll mention is that smoking rates declined quite a bit since about 1970, and smoking, cigarette smoking actually suppresses appetite and reduces body weight, and so I think one factor that probably played a role as well, in addition to all these changes in our food environment, is the withdrawal of that body weight suppressing effect of cigarettes, ’cause most people smoked back then, you take that away and you’re gonna accelerate the fat gain.
Brett McKay: Right. And also, instead of taking a smoke break, well, I’ll go get a Twinkie, or whatever, it’s something to do.
Stephan Guyenet: Could be.
Brett McKay: It could be. Well, and besides that, you also talk about… You tallied research how we just move less, we don’t work as… Back, our great-grandparents, they were probably a farmer, and today, we… Now, we just like… A lot of us are just working from home, we just go from the bed to the desk in our office.
Stephan Guyenet: Yeah, that’s absolutely right. And I think that probably played a bigger role in the changes in weight that happened over the first half of the 20th century, compared to the last half, ’cause by the time you get to the 70s, most people had more sedentary jobs by that time, but certainly in the earlier part of the 20th century, most jobs were extremely physically-intensive, not just farming, but working in factories, that most of these things were not mechanized or they were only lightly-mechanized. So, if you were working on an assembly line in a plant, producing cars, or even just selling clothing or washing clothing or… Almost anything that you can imagine was pretty physically-intensive, and the things that we did at home were physically-intensive too. Remember, we didn’t have washing machines, we didn’t have dryers. Most people didn’t have cars for most of the first half of the 20th century, so you had to get around by foot or public transit, or even on a horse. So just living life was more physically-intensive. A lot of the things that we had to do manually back then are now mechanized. And so I think definitely physical activity is a factor, but probably more the changes that occur in the first half of the 20th century, I would guess.
Brett McKay: Alright. So let’s dig into why our brain wants us to eat more than we need. And you talk about… It all starts, we have this reward system in our brain that kick starts our desire to eat. What’s involved here? What’s going on with that reward system in our brain? And what kinds of food does it want us to eat?
Stephan Guyenet: Yeah, so we… Yeah, so let me explain what the concept of reward is first. Reward is essentially… Food reward is the seductiveness of food. So, food, depending on its properties, has the ability to spark the motivation to eat enough. So imagine you’re sitting around and you… Suddenly, a pizza comes out of the oven, and you smell it, and you see it, and suddenly you really wanna eat that pizza, that motivation, that desire. So reward is that motivation, is that desire. It’s the pleasure that you get as you eat the pizza, and it’s also the learning, and this is something that happens beneath our conscious awareness, we’re not aware that this happens, but it’s the learning that happens that causes your brain to decide how motivated you should be in the future for similar types of foods. And so, essentially, the brain is hard-wired to learn to be motivated by specific food properties, so these include fat and carbohydrate, like starch and sugar and salt and protein and umami, which is that meaty MSG, soy sauce flavor that most of us are familiar with. And essentially, we are hard-wired to prefer these food properties and we will seek them out, and we will learn over time which foods supply them. And the way we do that is via a neurotransmitter called dopamine.
So when you eat… And this… Just in the last couple of years, this concept has really been fleshed out, so I’m really happy to be able to actually give more detail today, or at least a more complete picture today than I even could at the time that I wrote my book a couple of years ago. So, essentially, what happens is, when you eat food, that food goes down into your digestive tract, and your digestive tract, through receptors in your mouth, but mostly in your small intestine, detects the composition of that food. So there are receptors that are detecting carbohydrate and fat and protein and salt, and everything, and those receptors then send signals up to your brain. And this is all non-conscious, or at least most of it is non-conscious. Stuff happening in your small intestine is non-conscious. It sends signals up your vagus nerve, which is an information highway between your guts and your brain. And it sends that up and it informs your brain of the things that are in that food. And depending on the concentration of those things in the food determines how much dopamine gets released in your brain. So, essentially, your brain says, “Oh man, this pizza has tons of fat and carbohydrate and salt in it, so I’m gonna release a bunch of dopamine, indicating high concentrations of those desirable nutrients.” And what that’s gonna do is it’s gonna motivate you to eat more pizza, and it’s gonna set your motivational tone for the next time you encounter pizza.
So, the next time you encounter that pizza, your brain knows. Your brain has correlated the fat and starch and salt with the appearance of the pizza, with the smell of the pizza. So, the triangular slices, the greasy box, where you ate it, who you were with, what the situation was, everything, those became motivational triggers. So then, next time, all you have to do is smell the pizza or see the pizza or be in the conference room where you normally eat pizza, and that triggers the dopamine again, and that gets your motivation going. So that triggers… Another way of saying that is that you experience a craving. Once that dopamine hits, because it was triggered by that cue that your brain had previously associated with carbohydrate and salt and fat, once that cue is experienced by your brain, then it triggers the motivation to eat.
So that’s basically how your brain learns to motivate you to eat food properties that were important to the survival of your ancestors, ’cause you have to remember these food properties, to our distant ancestors, hunter-gatherers would have been extremely critical for them to obtain in a natural environment, because most of them are supplying the calories that they need to fuel their bodies, and then others are supplying critical nutrients that are scarce and natural, unrefined plant foods like salt. Salt is not something you can just get very easily by going out and eating random edible foods in the forest. Salt is something that you need to kind of seek out either through sea water or mineral deposits, or… Different cultures had different ways of getting it, but, as mammals that sweat, we actually lose a lot of salt, for a mammal, and so we have this special need for it, and that presumably explains why salt, sodium chloride is literally the only micronutrient, that is to say, vitamin and mineral that we can actually taste in our food.
Brett McKay: Alright. So, just to recap here, there’s particular foods, fatty foods, sugary, salty, umami foods, back then, those were essential for our survival. Today… And so our brain, as a consequence, has this system in place where dopamine is released so that, whenever we encounter these foods, we learn that we should want this. And so, every time we see it, we have that desire, that craving. I think it’s important to think… Oftentimes, people think of dopamine is the pleasure neurotransmitter, but it’s not. It’s just about wanting. You can eat something and not really like it, but you could still want it, like a drug is a good example. You might not like the drug, but it causes that dopamine so it makes you wanna want the drug over and over again.
Stephan Guyenet: Exactly, yeah. And thanks for bringing this up. So this idea that dopamine is the pleasure chemical is an idea that originated in the scientific literature. It was a hypothesis that was proposed decades ago and quickly refuted, essentially, but it kind of dug in its heels in the popular mind, and it’s been self-sustaining since then. So you see this claim a lot in the popular press, but really, the evidence doesn’t support it. Dopamine is really all about motivation. Dopamine is what causes cravings, it’s what causes you to want things at a really visceral level. It’s not the abstract wanting. It’s the really visceral craving-type wanting that dopamine mediates. And it also mediates that learning that teaches your brain how to crave in the future.
And I wanna mention… While we’re on this topic, I wanna mention that, as I said, the concentration of these dopamine-stimulating nutrients determines our motivation levels and how strong our cravings are. And also when you put them in combination. So when you mix the fat with salt or you mix the fat with sugar, that’s a lot more tempting than if you’re eating those things alone. So think about eating a bowl of ice cream, think about you subtract the sugar or think about you subtract all the fat. That’s not nearly as seductive as eating ice cream itself, which has the sugar and the fat. And so today, essentially, through technology and affluence, we have refined the art or the skill of refining these dopamine-stimulating nutrients to their utmost levels of purity and mixing them together in ways that maximally-stimulate our dopamine and create really strong motivational drives, really strong cravings to eat those foods that are probably stronger than anything our ancestors experienced, eating whole natural foods found in their environment.
So I think, essentially, we have the situation where these foods that we’ve created are just too good at doing what they’re trying to do, and that’s creating these negative consequences for us in the form of overeating and eating less-nutritious foods.
Brett McKay: Alright. So, yeah, so that’s the first problem there with today’s foods, basically, it hijacks our reward system. I think you give the example, like the Dorito is the perfect combination of fat, carb, umami. And you eat one, you’re just like… And then you’re eating the whole bag because it’s just that perfect combination of fat, carbs and savoriness.
Stephan Guyenet: Yeah, I don’t think I used that specific example in my book, but I think that is a relevant example, absolutely. If you deconstruct what a Dorito is, it’s concentrated carbohydrate, plus fat, plus salt, and then you have these other seductive flavorings on it as well that may contribute. And a Dorito is very calorie-dense. The thing that affects calorie density the most is the water content of foods. So when you think about an apple, it’s like 80 plus percent water. When you think about a steak, it’s like 75% water. Dorito has almost no water, and so that’s a very calorie-dense food that is delivering this really concentrated combination of dopamine-stimulating nutrients to your brain. But I think the one that takes the cake is actually chocolate. So, chocolate, of course, contains very little water also. So, it’s very concentrated, high in fat, high in sugar, but the thing that puts it over the edge is it actually contains a habit-forming drug called theobromine. Theobromine is similar to caffeine, in that it’s this mild habit-forming drug, but that plugs right into the dopamine system too.
So when you get this really concentrated combination of fat plus sugar, and then you add a habit-forming drug on top of it, you’ve got a really powerful combination. And I think that explains why, in studies, they find that chocolate is the number one most-craved food among the general population, but particularly among women.
Brett McKay: Alright. So we got really palatable food. And you highlight these studies that show that food palatability, or how tasty your food is, it has this combination of fat, that can affect whether we seek it out. And I think you talk about this experiment where when people are given unpalatable food… So there’s this experiment done in the 60s, I think, where there’s this machine where it put out this… I don’t know, it’s basically like Soylent Green, just this nutrition shake, and you could take as much as you want, but it had no flavor, but it had the perfect combination of fats, proteins, carbs that you needed, but it wasn’t good, and people really didn’t… They just drank as much as they needed, and that was it. They didn’t really… They didn’t overeat on this stuff.
Stephan Guyenet: Yeah, absolutely. It’s a pretty crazy experiment. Yeah, they had people in a hospital that were inpatients, for various reasons. And like you said, they gave them access to this machine that dispensed I think it was 7.4 milliliters of this bland liquid formula, is what they called it every time they pressed a button, and it just dispensed it through a straw into their mouths. And so they could… Anytime they wanted, they just grabbed this thing, pressed the button, put the straw in the mouth, and they got 7.4 mils. And, so, essentially, you’re stripping everything pleasurable away from the eating process. And what they found was, really interestingly, people who were lean actually continued to eat their usual number of calories. So they continued to eat their maintenance calorie intake, and their weight didn’t change. People who had obesity, their calorie intake dropped dramatically. And as you said, they were not asked to reduce their calorie intake, they were just given a system and said, “Eat as much as you’d like, however you need to feel full,” and their calorie intake plummeted, and they started rapidly losing weight. And they saw this across several individuals, and then it was replicated by a later study as well.
Yeah. So I think that just goes to show how much these properties, these food properties contribute to our eating behavior. And there’s plenty of other research that supported that too. So there are randomized controlled trials, which is a particularly rigorous type of study design where they give people different foods with different types of flavorings, some of which are intended to taste good and some of which are intended to taste a little weird. And unsurprisingly, this is kind of common sense, but people ate more of the foods that tasted good. And I should specify when you only gave them that versus only the other type of food, they ate more total calories of the good-tasting food. And these foods were nutritionally-identical, so we’re talking about literally just using different flavoring agents on the same sandwich. So, the flavor itself, how much do you enjoy it, how much reward value it has, how seductive it is, is a way that I like to put it, really does impact your food intake. And if we look across typical diets, you can see that variation in how good people report the food tasting has a large correlation with how much they eat at each meal.
Brett McKay: And now back to the show. Alright. So not only is food today, processed food, it’s designed, it’s designed to be more rewarding, so we eat more of it, and our brain wants that, so that’s one thing going against us, but another thing that’s different about today’s food environment compared to, say, 50, 60, 100 years, 1000 years ago, that we have… There’s more variety of food. And that’s another factor, I think, what role does variety play in the neuroscience of eating.
Stephan Guyenet: Yeah, absolutely. So one of the earliest things that alerted me to this was this really cool study. I think Barbara Rolls was involved in this, at least I think this study is really cool ’cause I learned something, but they had mice in different cages, or I think rats in different cages, and they were giving them just regular rat chow, but what they would do is they would put… In addition to that rat chow, they would put different tasty foods into these rats’ cages. So I don’t remember exactly what they were, but it was like cookies and sausages and some other tasty food, and they would put them in one at a time. So if you just put cookies in, they would eat more and they would gain a certain amount of weight, but if you put all three of these different types of tasty foods in at the same time, so the cookies and the sausages and the whatever else it was, crackers, then they would gain a lot more weight than if you had just put one food in. Even though the one food is already quite unhealthy, it’s already calorie-dense, should be perfectly fattening, so it really was the variety, per se, that was having a big impact on how much they were eating and how much weight they were gaining. And to this day, the most effective way to fatten a wide variety of non-human species is to put a variety of tasty human junk foods in their cage, and let them eat as much as they want.
Literally, human grocery store food, the types that most of us would recognize as unhealthy, is the most fattening food in the world to a wide variety of non-human species. And so I think it’s pretty… I think that is a pretty good piece of evidence that it’s probably a big factor in fattening humans too. So you can… Just to expand on this a little bit, you can take rats, you can put them on a high-fat diet, they’ll gain a certain amount of weight. You can put them on a high sugar diet, they may or may not gain weight, depending on the study, but… And you can even compare… You can combine fat and sugar and they’ll gain more weight than just the fat alone, but none of those diets even comes close to human junk food, to giving them access to a variety of human, tasty junk foods. It blows away any kind of macronutrient composition that you can put into a rat pellet. So, it’s about way more than just the nutrient composition. It’s really about the presentation and how seductive that food is.
Brett McKay: And the research shows that the same thing happens with humans, right?
Stephan Guyenet: Yeah, yeah, absolutely. Yeah, so it does work on humans, and this has been demonstrated in a number of studies. I think Barbara Rolls is the researcher who spearheaded a lot of those. And essentially, if you put people in a situation where they can eat foods… Again, you can even do this with nutritionally-identical foods where you’re only changing the flavoring… People will eat more if you have a variety of different flavors than if there’s only one flavor, even, again, if it’s nutritionally-identical. And so we call this the buffet effect. When you go into a buffet, most people have had this experience where you go into a buffet and you end up just eating way more food than you think you should, and that happens particularly more at buffets than in other settings.
That’s been my experience, and I think that’s been a lot of other people’s experience. And the reason is that incredible food variety. Our brains essentially are designed, for whatever reason, to have this thing called sensory-specific satiety, which means that we get satiated on a specific type of flavor profile, but not necessarily on other types of flavor profiles. So, if you have your steak, you might not want any more steak or you might not want any more meat, in general, but that doesn’t stop you from wanting more cake. Or if you have a bunch of cake, you might not want any more cake. You might not want cookies but maybe you still want steak. So that’s called sensory-specific satiety. And that explains… I think goes a long way toward explaining the impact of food variety on food intake and body fatness.
Brett McKay: No, I think we’ve all experienced that, the buffet effect. You just feel gross and you’re like, “No, I gotta try that thing because it’s different.” Or like, yeah, the dessert. You’ve eaten a big meal, like Thanksgiving, so there’s a lot of variety at Thanksgiving, you’re full, but then the pie comes around, like, “Well, I got room for pie,” even though you probably really don’t.
Stephan Guyenet: Exactly, I think this is a really great example of how our food intake is not just determined by our nutritional needs. It’s not just determined by the nutritional composition of the food or the calorie value of the food, or just hunger, in general. A lot of people really focus on hunger as a determinant of our food intake and body fatness and weight loss. And it is important, don’t get me wrong, but hunger is not the big picture… Excuse me, it’s not the only part of the picture. So, yeah, think about you’re at a restaurant and you’ve just had a meal of… You had a steak and a potato and a salad, and you’re full. You’ve eaten already probably more calories than you needed to eat at that meal. You’re totally full. If someone put another piece of steak and another potato in front of you, you wouldn’t touch it, you wouldn’t wanna touch it, yet, the waiter comes around with a dessert menu, and suddenly, you’re ready to eat a piece of cake or you’re ready to eat a brownie and ice cream, or whatever it is. And that’s because of the sensory-specific satiety, you’re not full on cake and brownies, you’re full on steak and potatoes. And also, of course, these are very, very seductive foods. Desserts are very, very seductive foods that really spike a lot of dopamine.
Brett McKay: Alright. So we got two things, we talk about two things in our modern food system, chlorically-dense, high-reward food, a variety of it, and the other thing that’s changed compared to, say, our ancestors, that food now is readily-available, it’s easy to access. All this stuff is easy to access. Before, if you wanted to get honey, you’d have to find a beehive and then stick your hand in a bunch of angry bees and get stung. Today, I can just drive… I could walk over to QuikTrip, and get a Taquito, and pay just a buck 50 for it.
Stephan Guyenet: Absolutely, yeah. And I think that is especially apparent if we’re looking over very long timelines of human history, like what you’re talking about. If you’re a hunter-gatherer, you have to put in a tremendous amount of effort to get your food. That is literally your job, getting and preparing food. That is what you spend hours on every day, and it requires a lot of time and also a lot of effort to make that happen. And that’s what our motivational systems in our brain are tuned to. Our brain is calibrated to create enough motivation to make you walk or jog five to eight miles a day, climb up trees, get stung by bees to meet your calorie needs. That is what your brain is calibrated to in terms of generating motivation to get food, but today, the effort barrier is so low, but we still have that same eating drive. And so something like what we call gluttony today, I think is a really instructive example. We have a… I can’t speak for all cultures, but at least in prevailing Western culture, we have this negative judgment around gluttony, this word gluttony, overeating. This is something that we think is bad, and we try not to do it very much. We feel guilty about it. But if you go back to hunter-gatherers, there’s no such thing as gluttony.
For them, eating as much as possible is awesome because it’s really hard to get that food. So when you get the opportunity to get a really easy win and eating tons of honey or tons of oranges or tons of fatty meat, you’re gonna take it, and that’s good. There’s no downside, because you’re making up for other times when you might not get as much food or when it might be harder to get food. So this idea of gluttony, I think, really highlights this disparity between how our brains are set up and how our modern food environment interacts with us. That’s essentially us trying to culturally-protect ourselves against this issue that we’re faced with. So, yeah… So I think that today it’s obvious to anyone, I think. You walk into a grocery store and there are many options for food that you really have to do little or no work to consume. We eat out way more than we ever have in human history. In the United States today, we spend about half of our disposable… Half of our food-related expenditures is on food eaten away from home, like restaurant food, fast food. Whereas, we only spent about a tenth of our food-related expenditures on food away from home, back 140 years ago. We have data going back that far, and that’s what it suggests.
So, there’s been profound changes in the convenience of food in this country, and essentially, your brain, whenever you’re thinking of doing anything, whether it’s shopping or negotiating for a job or making food decisions, your brain’s always doing cost-benefit analysis. So it’s saying what is the benefit of this food in terms of its calories and how seductive it is, and what are the costs in terms of how hard I have to work for it? How much money does it cost? And how much time is it gonna take me to do this? And essentially, the cost of food in terms of, again, the money and the time and the effort cost have gone way down over the course of human history, but particularly over the last century. I mean, food is historically cheap in the United States. We like to complain about the cost of food, but it’s literally cheaper than it’s ever been in all of human history. We spend about 10% of our disposable income on food today. So I think that all of the downsides, all the costs of eating that we would have experienced historically have been minimized to an extreme degree. And there’s benefits to this. There’s way less starvation happening in the United States than there was 100, 200, 300 years ago, and that’s a wonderful thing. So I don’t wanna present this as it’s all a bad thing, but there have been costs, and one of those costs is obesity.
Brett McKay: Well, and it sounds like just from understanding the rewards to our brain and the things that influence it, so the palatability of the food, the variety of it, the cost of it, from there, people… There’s insights there on how you can control your eating so you’re not consuming as many calories. And it sounds like don’t buy the cookies and potato chips, stick to basic foods like oatmeal, rice, meat, eggs. Don’t have a huge variety of… I mean variety of bad food, and then make it easy to eat the good food and harder to eat the bad food.
Stephan Guyenet: Absolutely, yeah. And some of this stuff that we’re talking about boils down to pretty simple principles that aren’t going to be a big shocker to anybody, like eat simple less-processed foods. But I think there are some things that are a little bit more counterintuitive to people, like I think people are used to thinking that their food has to be delicious every time, and I think that that is an idea that’s kind of been drilled into us by diet marketing, like there’s… Every diet… What diet is gonna say, “Hey, this is a bland diet.” No diet is gonna say that. They’re all gonna say, “You’re gonna be eating the most delicious food you’ve ever eaten in your life, and you’re gonna be losing weight.” It’s part of the sales strategy, but the truth is that that deliciousness itself is one of the things that is holding you back from eating a more appropriate number of calories for your weight loss goal.
And so that is one thing that I think is a little more counterintuitive. And of course, the diet has to be satisfying enough that you stick to it. I think you don’t want to eat a diet that just tastes bad, you’re not gonna stick with it, but I think we can eat things that are simple and satisfying, that are more like what our distant ancestors used to eat, just simpler things like simply-prepared meats and vegetables and nuts, and fresh whole fruits and limiting added fats, limiting added sugars, and other things that are very concentrated dopamine-stimulating nutrients.
Brett McKay: And did this… I was gonna say did this idea of your food has to be delicious all the time, you highlight this tribe, the ! Kung San, I think they’re in the Kalahari Desert, and you’ve pointed out that they… Occasionally, they get some honey, they get a truffle which they’ve just… They gouge on. But it says… But due to the limitations of living in a natural environment, they eat certain other foods daily without much enthusiasm. It’s just like, it’s just fuel.
Stephan Guyenet: Yeah, absolutely, and that’s what you see in hunter-gatherer cultures. I think most people in cultures like ours are accustomed to having their palates entertained with everything that crosses their lips, but I think most of us would be severely-disappointed by the diets that hunter-gatherers eat. If you actually really look at what hunter-gatherers eat, and again, this is what all of us ate prior to, say, 12,000 years ago, they didn’t have ovens for controlled temperature baking and roasting. They weren’t sautéing onions. They didn’t have sugar and white flour and added fats, at least most of them didn’t have added fats. And so we’re talking about taking a piece of meat and throwing it on the fire with no salt on it, or burying it in the sand next to the fire. We’re talking about eating fresh fruit. We’re talking about eating plain roasted nuts with nothing on them. We’re talking about eating tubers that had weird off flavors, like sometimes they were bitter, sometimes they had other flavors that we wouldn’t necessarily enjoy. Tons of fiber sometimes in these tubers, so much that you might have to spit out a lot of it as you’re eating it.
Some of the fruits they ate were not very sweet. It depends on the fruit. Some of them were sweet, some of them weren’t, but some of them were not very sweet, and so you’re eating this kind of tart, not very sweet, fibrous fruit. So that’s a lot of what they were eating day in, day out. And so that’s not to say that they never had foods that were tasty, again, sometimes they did, but I think that overall the diet was a lot less seductive, a lot less entertaining to the palette than what we eat today. And that’s not surprising. Today, we have incredible control over what passes our lips. Our distant ancestors, they ate what was available or what grew well in their area, but today, we can refine things, we can extract the dopamine-stimulating sugar or MSG or starch or fat, or whatever it is, from those whole natural foods, concentrate them and combine them into these really delectable kind of art forms for the primitive parts of our brain that judge these things. And so it’s just a very, very, very different picture that we have today.
Brett McKay: Alright. So we’ve talked about the food environment, and how it is designed, basically. It’s like there’s an evolutionary mismatch, like our brain wants these things at certain time in human history that was good, but today, it’s just too abundant and it causes us to overeat and we get fat. Then you also, in the book, talk about another part that’s driving us to feel hungry or not, and it’s this hormone called leptin. And I’m sure people who are listening to the show have probably heard of leptin if they read some stuff about health and fitness online, but can you walk us through what is leptin and what role does it play in our desire to eat?
Stephan Guyenet: Yeah. So, essentially, leptin is a key piece in the system that regulates body fatness in humans. And the way that system works is that… I’ll start with an analogy. So, if you imagine a thermostat, thermostat measures the temperature in your house. And then whenever the temperature deviates from whatever the set temperature is, it will either kick on heat or it will kick on air conditioning to bring it back to that set temperature, and that’s called a negative feedback system, or you call it homeostatic regulation. And these things are pervasive both in engineering and in biology. So there’s tons of things like this in the human body, for example, temperature regulation is a great example. So the way the system works for regulating body fat is that you have this hormone, leptin, that is produced by your fat tissue in proportion to its size. So, the more fat you have, the more leptin gets produced. That enters your bloodstream and is detected by parts of your brain, and those parts of your brain essentially compare it to what they think it should be. And if your body fat level starts to drop, let’s say you’re going on a diet and your body fat level starts to drop, the leptin goes down, your brain is informed of the fact that your body fat is going down via declining leptin levels. And then your brain kicks in this suite of responses to bring the fat back. So your brain makes you hungrier, your brain makes you crave foods more.
Your attention is shifted to pay more attention to foods. You might find yourself having a harder time walking by the cookie aisle. And at the same time, if you lose enough weight, your metabolic rate also starts to decline. So, your brain actually starts to shut down your metabolic rate a little bit. Essentially, what your brain is trying to do is bring in more calories and reduce the number of calories leaving so that you’re able to squirrel away more into your fat mass to bring that back to where it was. And the thing that really sucks about this system is that it will actually regulate, it will defend against fat loss, even in people who have obesity. So even in someone who really carries more fat than is healthy, their brain is still gonna defend their current level of body fat. So when your leptin level starts to drop, your brain is gonna say, “No, I don’t like this.” And it’s gonna kick in that same starvation response, ’cause that’s exactly what I just described, it’s literally a starvation response, it’s gonna kick in the same starvation response that it would kick in if a lean person started to lose weight. So, someone who was actually really starving, like their body fat stores were depleted and they’re actually under real physiological threat, they’re gonna kick in a certain suite of responses, and of course, this is all non-conscious, it’s happening from non-conscious parts of their brain, they’re gonna kick in this protective starvation response.
Someone with obesity has the same thing when they start to lose weight, so that’s really something that’s really challenging about how human biology is set up. And so, when you look at randomized controlled trials, again, that’s this rigorous type of study of different weight loss approaches, what we see, generally, is that people can lose weight on almost any diet, but also on any diet, people will start to rebound after their period of maximum weight loss. So, generally, in these studies, you see maximum weight loss around six months, and then people will start to regain weight. And essentially, what’s happening or… I don’t wanna say this is the entire picture, but a key part of what’s happening is that people are losing the battle against their own non-conscious brain that is trying to bring that fat back. They’re losing the battle against these brain regions that are actively undermining them and creating a struggle for them, where they’re having to fight their own impulses to maintain that weight loss.
Brett McKay: No, I think everyone who has tried to lose weight have experienced, they lose the weight and then they gain it back, and we’ve seen this dramatically on shows like ‘Biggest Loser’, right? People lose lots of weight, and then you follow up with them a year later, and they’ve gained it all back. And I guess that’s leptin, there’s no leptin there, and their brain’s like, “You guys get back to where you were.” And so you start eating more and that’s what happens.
Stephan Guyenet: Absolutely, and it’s like stretching a rubber band, the harder you stretch it, the more resistance you feel. And so for someone who has really lost a lot of weight, like people on the ‘Biggest Loser’, they’re gonna have an extreme starvation response that is driving them back toward weight gain. And, as you said, you follow up with these people a year or two later, most of them have regained most of their weight. And I don’t wanna… A lot of times, this comes across as really negative and hopeless, I don’t wanna come across that way. I don’t think that it is hopeless to try to lose weight, but I do think that there are challenges that are because of how the human brain and human body is constructed. And I think it’s really helpful for people to understand those challenges because then they know what they’re gonna be up against, they’re prepared, they’re not gonna be… Feel like a failure when they hit those barriers, and maybe they’ll have better tools to help overcome those barriers. And also I think it helps people not be as judgmental. If it were easy to lose weight, if we didn’t have these barriers, probably there wouldn’t be very many people with obesity, right? These are the things that are making it difficult and undermining people’s well-intentioned efforts to lose weight.
Brett McKay: Well, are there any insights from neuroscience that can help people manage that leptin battle? Is it just a matter of, okay, you know what’s gonna happen, so you need to have a plan, and maybe you just have that plan and you stick to it, even though your body is like, “No, eat the cheesecake.”
Stephan Guyenet: Yeah, so I think… So there are a couple of different ways you can approach it. And these are… The first one I’m gonna explain is a little bit of a caricature, but I’m just doing it to prove a point. There’s the kind of pure willpower approach, where you say, “Hey, I’m gonna keep eating the same foods that I’ve always been eating, maybe my diet started off unhealthy, I’m gonna keep eating the cookies and the cake and the fried chicken, and I’m gonna keep eating all that stuff, but I’m just gonna use portion control, so I’m gonna try to eat half as much as what I used to eat. And I think that’s the situation where you’re really gonna be setting yourself up for struggle, because when you do that, your brain doesn’t like it. The amount you were eating of those foods before was the amount that your brain was intuitively telling you to eat, right? ‘Cause the way we eat is we sit down and we keep eating ’til we’re full, and then we stop eating. That’s the natural way of interacting with food, for a human. And so you’re forcing yourself to not indulge your impulse to eat until you’re full. And so you’re setting up a struggle between your higher-order cognitive willpower parts of your brain and the lower-order intuitive impulsive parts of your brain. And that’s a struggle that most people just can’t win in the long-term.
Some people can. It does work for some people, and they can do it. Some people just have an iron will, but I don’t think most people do, and I don’t think most people should expect themselves too, ’cause it’s just not really how the human brain is set up. So I think a better way is to set up the situation so that you don’t have to exert all that willpower. So you set up the situation in such a way that you’re actually trying to change those impulses, you’re trying to directly change how you’re interacting with those non-conscious part of the brain that are generating those impulses. And so that’s, just to give you a couple of examples that are particularly important, changing your food environment so that you’re not feeding your brain food cues all the time. So, again, when you see these… When your brain gets these cues, like the sight of food or the smell of food, that triggers dopamine release, that triggers your motivation to eat. So if you eliminate those cues, you’re going to reduce your motivation to eat more than you want to, and things that you don’t want to.
It’s the same thing as someone who’s trying to quit smoking, you don’t leave packs of cigarettes hanging around the house, you don’t go to the places you used to smoke, you don’t hang out with people who are smoking. You’re trying to eliminate those cues that are going to cause you to relapse into that dopamine-driven behavior. So that’s one thing. And then another thing is to eat foods that create greater levels of satiety or fullness per calorie in the parts of your brain that process fullness, the feeling of fullness. And the feeling of fullness that you feel is only loosely-connected to the number of calories you eat, but it’s more tightly-connected to food properties, like how calorie-dense the food is, in other words, how many calories per gram or per volume. So if you have food that is very, very calorie-dense, like chocolate or bread is pretty calorie-dense, for the same number of calories, it doesn’t fill your stomach up very much. So 100 calories worth of those foods is not very much volume.
Whereas, if you’re eating a bowl of oatmeal or a piece of fresh fruit or a piece of fresh meat, that is mostly water, so it actually, per calorie, fills your stomach up more, and that sends signals up to your brain that actually makes you feel full. And so you end up feeling full, having consumed fewer calories. And again, since we sit down and just keep eating ’til we feel full, that’s the intuitive, natural way of interacting with food, you could eat half as many calories and feel just as satisfied if you’re eating unrefined water-rich foods than versus if you were eating processed calorie-dense foods. So that’s another thing. So it’s not just the calorie density, it’s also the protein content that makes you feel more full per calorie. It’s the palatability, so how delicious it tastes. The more delicious the food it is, the less filling it is per calorie. And the fiber content, the more fiber is more filling. So just setting these, setting up your food environment, setting up the types of foods that you’re going to eat at a meal can actually help control those impulses in the first place. So, instead of struggling against hunger and struggling against cravings, you’re actually nipping those in the bud beforehand, so you’re not having to, day after day after day, fight yourself and whip out that willpower every time.
Brett McKay: Well, and two other factors you highlight about modern life that causes us to overeat is we don’t sleep enough, we’re bad sleepers and we’re stressed out. So what role does sleep and stress play in our desire to eat?
Stephan Guyenet: Yeah. So, sleep, there have been some studies… Sleep’s pretty interesting. So you look at the observational studies, so these are ones that just say, we’re gonna look at a bunch of people, we’re gonna see how much they sleep and how much they weigh, and how their weight changes over time, and then we’re gonna see if there’s any relationship between those two things. And those studies find that actually sleep… Short sleep is really well-correlated with weight gain over time. So people who sleep less than six or seven hours a night tend to gain more weight than people who don’t, and it’s a pretty big correlation.
Of course, you might say, well, that could be confounded. It’s observational. What does it really mean? So there have also been these short-term randomized controlled trials, again, that’s a really rigorous study design where they actually restrict people’s sleep in one group and not in another group, and then they compare their calorie intake, and what they find is that when you restrict people’s sleep, they eat more, and it’s a pretty significant effect. I don’t remember exactly what it was, but I get into detail in my book it’s like 150 calories a day, something roughly on that order. And you’re sleeping less, you’re actually burning a little bit extra energy too but not enough to make up for the extra food that you eat. And basically, what it looks like is that it kind of turns on your brain’s appetite systems. When you put people in an FMRI, which is a kind of brain scan, and you look at their brain activity when they’re looking at images of food, they have more activity when they haven’t slept enough. So, basically, their brain is getting more excited about eating food then it would if they had slept enough. And so essentially, yeah, this paints a picture where sleep causes you to eat more… Or excuse me, insufficient sleep or low-quality sleep tends to cause people to eat more.
I don’t wanna say that the evidence is super-ironclad, but I think it pretty strongly suggests that is happening, at this point. Then, as far as stress is concerned, there are surveys that have been conducted by, I think, the American Psychological Association, that suggests that people react really differently to stress. So I think it’s roughly 45% of people report overeating when they’re stressed, and then 30 some percent of people report actually skipping meals. And so it has this really different effect on different people, but a lot of people do start to over-consume when they’re stressed, and they particularly fall back on comfort foods, which are usually these calorie-dense foods that we would normally think of as not very healthy, and pretty fattening, mac and cheese, and ice cream, and cookies, and that sort of stuff.
Brett McKay: So, bottomline there, get better sleep, practice good sleep hygiene, that can help, won’t hurt, and then manage stress in other ways besides eating food.
Stephan Guyenet: Yeah, absolutely.
Brett McKay: Well, Stephan, this has been a great conversation. Is there some place people can go to learn more about the book and your work?
Stephan Guyenet: Yeah. So the book is available from any place that sells books. Amazon is an easy place to get it. My personal website is stephanguyenet.com, or you can… If that’s too hard to spell, you can do wholehealthsource.org, that’ll take you to the same place. I haven’t been really active on my website yet lately, but I do… I am fairly active on Twitter, although, since coronavirus, I haven’t really been… Had as much time to write about health and nutrition topics. But I do also wanna recommend another website called Red Pen Reviews, which is an organization that I founded along with some other nutrition experts that posts authoritative reviews of popular health and nutrition books, and that’s at redpenreviews.org.
Brett McKay: Fantastic, I’m gonna check that out. Well, Stephan Guyenet, thanks for your time. It’s been a pleasure.
Stephan Guyenet: Alright. Thank you, Brett.
Brett McKay: My guest there was Stephan Guyenet. He’s the author of the book ‘The Hungry Brain’. It’s available on amazon.com and bookstores everywhere. You can find out more information about his work at his website stephanguyenet.com. Also check out our shownotes at aom.is/hungrybrain, where you can find links to resources where you can delve deeper into this topic.
Well, that wraps up another edition of The AOM Podcast. Check at our website at artofmanliness.com, where you can find our podcast archive as well as thousands of articles that we’ve written over the years about pretty much anything you think of. And if you’d like to enjoy ad-free episodes of the AOM Podcast, you can do so on Stitcher Premium. Head over to stitcherpremium.com, sign up, use code MANLINESS at checkout for a free month trial. Once you’re signed up, download the stitcher app on Android iOS, and you can start enjoying ad-free episodes of The AOM Podcast. If you haven’t done so already, I’d appreciate if you take one minute to give us a review an Apple Podcast or Stitcher. If you’ve done that already, thank you. Please consider sharing the show with a friend or family member who you think gets something out of it. As always, thank you for the continued support. And until next time, this is Brett McKay, reminding you to not only listen to the AOM Podcast, but put what you’ve heard into action.