Why Do We Overeat? Podcast with Stephan Guyenet | humanOS Radio

Why do we overeat, even when we know it’s bad for us?

Like many questions in biology, part of the answer to this question is uncovered by an understanding of evolution. We know that animals have generally evolved to expend as little energy as possible in seeking and consuming energy-dense foods. All living things require energy to survive and reproduce, so it makes intuitive sense that genes associated with finding and eating lots of calories might be favored by natural selection.

This also applies to humans in natural environments. Hunter-gatherers, who live in conditions similar to those of our distant ancestors, gravitate to high-calorie fare, although they don’t find a great deal of it. When they do get something extra tasty and high in energy – like ripe fruit, fresh meat, and honey – they will gorge on it.

Modern humans are subject to these impulses as well. So, what’s different?

Our environments have dramatically changed. Rather than getting rare seasonal opportunities to indulge in rich foods, we are constantly surrounded by such delicacies. We did not evolve with any need to resist these kinds of tasty treats, so perhaps it is unsurprising that we so often fail to restrain our impulses despite our best intentions.

Guest

In this episode of humanOS Radio, I talk once again with Dr. Stephan Guyenet, this time about his new book, The Hungry Brain, which was just released this week. Listen to our first discussion here.

In his book, Stephan addresses the fundamental questions of why we overeat. We overeat because of evolutionarily-conserved circuitry in the brain, which drives us to indulge for short-term pleasure, even when we know it’s at the expense of our health and wellbeing. In the show, Stephan explains how these circuits work to regulate energy intake and body fatness.

Much of this is based on biology and genetic predispositions, but that doesn’t mean you can’t do anything about it. In fact, we discuss things you can do to manage these primal impulses in a fattening world, and to make sure that your daily behaviors are in alignment with your health and weight goals.

Tune in below for more!

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Transcript

Stephan Guyenet - 00:07: The human brain is always looking for a deal. It's always looking for the most benefit for the least cost, and this is true whether you're talking about negotiating with your boss for a raise, or whether you're talking about obtaining food.

Kendall Kendrick - 00:24: HumanOS. Learn, master, achieve.

Dan Pardi - 00:34: Dr. Stephan Guyenet, welcome back to HumanOS radio.

Stephan Guyenet - 00:37: Great to be here, Dan.

Dan Pardi - 00:38: You've just published a book called "The Hungry Brain: Outsmarting the Instincts That Make Us Overeat" I wanted to bring you on the show again to discuss this. First of all, when did you start working on the book?

Stephan Guyenet - 00:50: Yeah, I started working on the book almost exactly three years ago, and I have to give you a little bit of credit for this, because it was a conversation that we had that kind of sparked the whole thing, kind of set the whole thing in motion, got me thinking about taking some of the ideas that I had from my blog and actually turning it into a book.

Dan Pardi - 01:08: That is really great to hear, because you've been writing on your blog for a long time, you have a big following, and I think pulling all of the big ideas together into one cohesive, contiguous piece that you can read is really valuable. I'm proud of you that you did it, and let's just dive into it. Why are we so much heavier than traditionally-living cultures and even our own ancestors?

Stephan Guyenet - 01:28: Yeah, I think that's a really interesting question. Just to touch on some of the data on that, you can look at pretty much any traditionally-living culture around the globe, and what I mean by traditionally-living is cultures that have not been touched by industrialization of diet and lifestyle, and what you find if you look at those cultures, there's actually quite a bit of evidence on this, is that they tend to be a lot leaner than we are in modern, affluent nations. All evidence that we have indicates that this has been true for probably all of human history. We are heavier today on average than we ever have in all of human history.

02:08: We can see that happening even in the United States, if we look back far enough. If you go back to the late 1800s, what you find is that among white, middle-aged men, about 1 in 17 were obese, whereas today it's like 40% are obese. There's been a very, very marked change in the prevalence of obesity over time. By the way, I want to clarify a little bit. The reason I only shared data about middle-aged white men is because that's the only data we have, but we can compare that demographic back then to that demographic today, and it does suggest a very, very striking change.

02:50: This is a huge question, why did this happen? This is a huge question, and so many things have changed over the last 100 years, 200 years, thousand years. How do we get a toehold on this? How do we start to logically dissect this problem? What I like to do is, I like to go back to a really fundamental principle of body fatness which is calorie balance, so the number of calories entering the body versus leaving the body. We know that since body fatness is the primary energy storage site of the body, and this has been demonstrated experimentally many times, that the number of calories entering versus leaving is almost the exclusive determinant of the amount of fat that you carry on your body.

03:35: That kind of gives us an entry point into thinking about this, to say, "Hey, can we find any places where calorie intake has increased or calorie expenditure has decreased?" I think it's really not hard to demonstrate that calorie expenditure, at least on average, has decreased. In the United States 100 years ago, most jobs involved manual labor, and even just doing everyday tasks involved a lot of manual labor. They didn't have washing machines, they didn't have dishwashers. A lot of people kneaded their own dough, they plowed their own fields. They didn't have motor vehicles, so they were walking everywhere or riding horses. Those are things that demand a lot more energy than the day-to-day tasks that we do today, the corresponding types of tasks.

04:23: Calorie expenditure has definitely gone down. If we look at calorie intake in the United States, we can look back to the early 1900s, to about 1909, and the data become less and less reliable as we go back, but I think the general trends still hold. Interestingly, what you see is that in the early 1900s, calorie intake was pretty high, and then it gradually goes down, and down, and down, until the 1950s and 60s. It stays lower until the mid-70s, and then it starts to creep up. Then, in the 80s, it goes way up, and keeps going up until now, basically.

05:04: This is really interesting, because the higher calorie intake that we had at the beginning of the 1900s makes sense. We were burning a lot of calories, and so we had to eat a lot of calories. That's what you would expect, right?

Dan Pardi - 05:17: Right.

Stephan Guyenet - 05:18: Then, as we began fewer calories, over time, as our lives mechanized, our calorie intake went down, and down, and down, also as you would expect, because we need fewer calories. Over that time period, we were gaining weight, but not at a very rapid rate. We were slowly gaining weight. Then, around the late 1970s to mid-1980s, our calorie intake really started to skyrocket. That did not correspond to any increase in physical activity. Our calorie intake went back up higher than ever, actually, but it was not met in the corresponding increase in calorie expenditure.

05:58: Basically what happened was that there was a gradual and then sudden decoupling of calorie intake from our true calorie needs. This is why I really focus on the calorie intake side of the equation. Again, I'm not doing this to de-emphasize physical activity or calorie expenditure. I think that's also an important part of the equation, but I think you can out-eat almost any level of physical activity. The question is, why were we out-eating the number of calories that we needed to remain lean?

Dan Pardi - 06:31: Okay, so this explains the mechanism, but it doesn't explain what was driving it, except for the physical activity. What made us eat more calories?

Stephan Guyenet - 06:39: I think there are a variety of different ways to think about this, but what I really try to do in my book is I try to go back to first principles. I really try to get down to the very bottom of what drives an animal to eat food. We know that the brain was shaped by natural selection, and the currency of natural selection is reproductive success. In other words, having as many offspring as you can. A big part of having as many offspring as you can is obtaining sufficient food, and particularly sufficient food energy so you can run your body and build all the tissues that you need to build to produce offspring.

07:17: For that reason, brains evolved to generate behaviors that obtain food efficiently. This is true of our own ancestors, as well as every animal that has a brain. You can actually model how this works, and researchers have done this first in non-human animals using a discipline called optimal foraging theory. You can mathematically model basically how an animal will behave in the wild, how it will behave, what resources it will select, and why it will select them. If you model that behavior, what you find is that they primary driver of food foraging behavior is the calorie return rate.

07:57: What that means is, the is the equation. The value of a food item, and thus whether it's worth pursuing, is equal to the number of calories that food item supplies minus the number of calories required to obtain it divided by time. That's just a very basic equation of economics that is all about maximizing value per unit time. It's pretty satisfying to see this universal principle that applies to animals trying to find food, and applies to people trying to make money through investments. It's kind of cool to see that fundamental universal principle applied to all of these things.

08:33: I want to say that calories are not the only thing animals are looking for, but when you model their behavior, that is the number one thing. It's the single factor that explains most of their foraging behavior in a variety of omnivorous species.

Dan Pardi - 08:47: Okay.

Stephan Guyenet - 08:48: Yeah. It turns out that researchers have also modeled the behavior of human hunter gatherers, and they've shown that it also corresponds to this same type of principle of trying to maximize the calorie return rate. This makes sense. If you're a hunter gatherer, you're living in a dangerous world, and you're living in a world where it's not easy to get calories. I don't know how many folks you or other listeners have tried to go out in the wild and find enough calories to eat for a day, but it's not so easy.

Dan Pardi - 09:17: Yeah.

Stephan Guyenet - 09:18: These people have to build amazing skills for a lifetime to be able to do it successfully. You become efficient, and you go after the things that are going to get you the best returns for the least amount of time and effort.

09:32: This is how the human brain is wired. The human brain is always looking for a deal. It's always looking for the most benefit for the least cost, and this is true whether you're talking about negotiating with your boss for a raise, or whether you're talking about obtaining food. The way we obtain food, all this stuff is built into our brains more intuitively than it might be if we're negotiating with our boss about salary.

09:58: The part of the brain that regulates this economic logic is the orbitofrontal cortex and the ventromedial prefrontal cortex. What they do is they basically collect all kinds of information about the situation in question, and it's like a pro and cons list that's partly conscious, partly non-conscious. It integrates all that stuff, and it says, "Hey, what's the most valuable thing you could be doing right now?" To get to the matter at hand, "What's the most valuable food related behavior to engage in right now?" Then, once it's chosen that, it sends signals to the motivational parts of your brain to say, "Hey, let's do this." Maybe you'd experience a craving, or you would feel tempted by something, or you'd feel hungry, because it's integrating your energy state as well as all kinds of things about your environment.

10:47: Our brains are wired to look for good deals. Since the intuitive value of food to the brain and therefore how motivated you are to eat it has a lot to do with its calorie content as well as how easy it is to get, when high-calorie foods are readily available, hunter gatherers will gorge on them in a way that's really spectacular. It's striking. I spoke with some really top notch anthropologists during the research for my book, and Kim Hill, Brian Wood, Herman Pontzer. What they described to me was mind-blowing. Hunter gatherers chugging a quart of honey ...

Dan Pardi - 11:24: Oh my gosh.

Stephan Guyenet - 11:25: ... chugging it like it's milk, and eating 30 oranges in a sitting that are very similar to the ones you would buy in a grocery store.

Dan Pardi - 11:33: Wow.

Stephan Guyenet - 11:34: Eating, I can't remember whether it was five pounds or five kilos at a single sitting.

Dan Pardi - 11:39: Oh my gosh.

Stephan Guyenet - 11:40: Yeah, it's extreme.

Dan Pardi - 11:41: I don't know if I could do any of that.

Stephan Guyenet - 11:43: Yeah.

Dan Pardi - 11:44: I guess I could, I'm a human, but it sounds impossible.

Stephan Guyenet - 11:48: I know, it does, right? It does.

Dan Pardi - 11:50: I want to try.

Stephan Guyenet - 11:53: Most of us don't quite do it to that extent, but they don't have limits on their eating behavior. This is what all of the anthropologists told me. They don't have limits on their eating behavior. They don't need limits, because gorging on food when it's easy to get and calorie dense is good for them. That literally helps them. It doesn't hurt them like it does for us. It helps them get the energy they need to survive and produce offspring. There's no downside.

Dan Pardi - 12:20: Make hay when the sun's shining, right?

Stephan Guyenet - 12:22: Yeah, absolutely. Their brains, and our brains, because we descend from them, are wired to take advantage of those situations, to take advantage of great deals where the value of the food item according to that equation I described is very, very high. Most of us don't sit down and eat five pounds of meat, but I think we still have those impulses to eat perhaps more than is good for us when we're in those kinds of situations.

Dan Pardi - 12:50: Yeah.

Stephan Guyenet - 12:50: Yeah, and so our brains, they didn't evolve to regulate food intake on a conscious, rational level, they evolved to regulate food intake intuitively. All those impulses that were there in our hunter gatherer ancestors are still there for us, and we struggle with them, and we try to regulate them using our conscious rational mind, but it's difficult. Those tools are limited, because our brain wasn't really designed to regulate food intake in that way.

13:18: This brings us to the fundamental problem of overeating which is that none of us want to overeat, yet most of us still do. That implies that there are these non-conscious parts of our brains that are influencing our food intake behaviors, and that these brain circuits are driving us to overeat despite our best interest. These are those ancient circuits that we inherited from our hunter gatherer ancestors that were beneficial in the context of their lives. My book is all about what those circuits are and how they drive us to overeat.

Dan Pardi - 13:50: Fascinating. What makes some food so much more seductive than others?

Stephan Guyenet - 13:54: Yeah, I think this is a really great example of the non-conscious brain circuitry that drives us to overeat. The brain is literally hardwired to be motivated by specific nutrients in food, specific chemicals in food. Sensors in our mouth and our small intestine detect the chemical composition of the food that we eat, and these censors are looking for specific things. They're looking for starch, fat, sugar, amino acids that are found in protein, glutamate, which is that meaty, monosodium glutamate, umami flavor, and salt. Some of those things are conscious, we can detect them on our tongues. Others are non-conscious, and they're detected in our upper small intestine.

14:36: What they all do is, when those signals are detected, when those chemicals are detected, they send a signal to the brain that releases dopamine in a part of the brain called the ventral striatum. That's a key part of the brain that governs basic motivations. The more concentrated these substances are in the food, the more dopamine gets released. Dopamine is a teaching signal for the brain that reinforces behavior. When you eat foods that are concentrated sources of starch, fat, sugar, protein, and salt, your brain basically says, "That was really awesome," and then it learns to be motivated to seek those foods again in the future.

15:14: A lot of this learning process, by the time we're adults, this is well ingrained. We've eaten foods so many times, so many different kinds of foods, our food preferences are pretty well established. In kids, that's not true. Kids are still learning their food preferences, and they can be modified in adults as well. We're just not quite as plastic in that regard.

Dan Pardi - 15:33: Being interested in the subject and having a 3.5 year old boy, Desmond, it's amazing to watch a young person's experience around food. As soon as they have ice cream, the first time they have it, it's like, "Oh, what's this? This is interesting." Pretty soon, that's all he wants to have. He'll only eat other food so that he can have ice cream for dessert.

Stephan Guyenet - 15:52: Wow.

Dan Pardi - 15:53: It's so powerful, because they don't have the other parts of the brain developed, so he's not caring to look good in a swimsuit in the spring. All he wants is to eat ice cream only when he's hungry. It's been an amazing experience to first understand some of the neuro-circuitry, and then now to see it in action in a young child. It's very powerful.

Stephan Guyenet - 16:12: Yeah, that's amazing. Kids, they have all the instinctive circuits, but their cognitive control circuits are not so well developed. Yeah, that's amazing. It sounds like from what you were saying that it took him a couple times to really develop that strong motivation for it.

Dan Pardi - 16:27: That's right.

Stephan Guyenet - 16:28: Interesting.

Dan Pardi - 16:28: Yeah, like liked it at first, but just like you're describing, he learned over time that this provided a really pleasurable stimulus for him. Then, that is now what motivates him to eat his dinner, just so that he can have dessert. It's tough, because we care to feed him really healthy food, and we're constantly wagering with a small child who doesn't want to eat their vegetables and just wants to eat the really calorie-dense palatable stuff. It's amazing to watch.

Stephan Guyenet - 16:51: Yeah, that's an excellent example. That's exactly what I'm talking about. Your brain, it sets your motivation level, and in our everyday experience what we end up with is cravings for things like ice cream, brownies, pizza, chips, and a variety of other tempting foods that we enjoy but aren't really helpful for some of our high-level goals of being lean and healthy. What we don't end up with are cravings for low-calorie and low-salt foods like plain celery sticks and plain raw kale. This is exactly why most young kids don't really like vegetables, because the vegetables do not contain any of the stuff that the brain is instinctively looking for.

17:31: The brain doesn't really care about riboflavin, and magnesium, and calcium, and all these things. We can't taste it in our mouth, and we can't taste it in our intestines, either. This is speculation, but I think the reason why we can't taste those and they don't taste good to us is that those are things that if you were a hunter gatherer, it was pretty much impossible to meet your calorie needs without meeting those other nutrient needs, because the only thing you could eat, for most hunter gatherers, was an omnivorous, whole food diet. If you were able to meet your calorie needs and your protein needs, then you were pretty much good on the rest. We didn't really evolve to need to seek those things.

18:13: Kids don't really see any value in vegetables until they've been repeatedly paired with fat ans salt, and the brain has learned that those textures and flavors predict fat and salt. Then it's like, "Okay, yeah, I can deal with this. This is all right."

Dan Pardi - 18:27: I was having a conversation with somebody the other day about how Brussels sprouts have had such a resurgence that was everybody's least favorite vegetable when they were a kid, because they were boiled, and put on a plate, and they were gross. Now, they're fried in olive oil with salt, and it's a common appetizer at a lot of restaurants, and it's made them a lot more palatable by combining the two. Same with Lima beans. I don't know, Lima beans haven't had a resurgence, but they were part of the conversation as well, the most gross food growing up.

Stephan Guyenet - 18:54: Yeah, there's no food that I really dislike, but I don't love Lima beans or Brussels sprouts. I will say that, yeah, there are certain ways to cook them that make them a lot better, for Brussels sprouts. My wife's been helping me out with that. It's interesting to think about the context, because traditionally Brussels sprouts are considered a real delicacy if you go back 100 years ago. I think the reason is that Brussels sprouts, they produce in winter. They're one of a very few vegetables that actually matures in winter. It's this fresh vegetable at the time of year when there's no other fresh vegetables.

19:28: I think now it's like, you can get any vegetable at any time, so it's like, "Why would I care about Brussels sprouts? They taste mushy." If that was the only vegetable available, it might have been pretty amazing.

Dan Pardi - 19:39: Yeah, yeah, totally. I know that many people find that they will overeat when they're stressed. What is the role of stress in all this, as another sort of modifier to what types of foods you're seeking or wanting?

Stephan Guyenet - 19:51: Yeah, I think this is another great example of a non-conscious brain system that affects our food intake. Surveys have been conducting in the United States I think by the American Psychological Association that show that just under half of people report overeating when they're stressed, and something like a third of people report that they skip meals. It's very individual, but stress does have a very profound impact on eating behavior.

20:18: Just to give some background on how that happens, the brain contains a threat response system. This is a very, very deeply rooted system in many parts of the brain, because our ancestors were constantly dealing with threatening situations that were literally life or death. This is really, really deeply rooted in a lot of parts of the brain, and it can very profoundly change both behavior and physiology.

20:42: The threat response system, like I said, it's in many parts of the brain, and I don't mean to oversimplify it, but a very important part of the brain for the threat response system is a location called the amygdala. This is particularly important for stressors that are due to abstract concepts like the possibility of being laid off, or psychological stressors, or external threats, as opposed to having a bleeding wound and your blood pressure is dropping. That engages different threat response circuits in the brain system.

21:15: What the amygdala does is basically constantly alert and scanning for possible threats. It's connected to a lot of different brain regions, and it's always on the lookout for different threats. Some of these parts of the brain it's listening to are parts that process psychological stressors, like being stuck in traffic and getting in an argument with a loved one, and some of them are things that process more concrete external things, like having a football coming toward your head and having to duck out of it really quick, or you're trying to cross the street, and you see a car coming out of the corner of your eye. These are the types of things that the amygdala is constantly scanning for.

21:54: When it identifies a threat, what it does is it activates a broad swath of stress responses in the brain and body. It starts sending signals to a bunch of other parts of the brain that affect both your behavior and your physiology. There are a lot of different elements to this, and I won't get into all of them, but one that I think is particularly relevant here is that your brain activates an arm of the threat response system that's called the HPA axis, the hypothalamus, pituitary, adrenal axis. I won't get into all the details of that, but the end product of that is cortisol, a hormone produced by the adrenal glands that sit on top of your kidneys.

22:34: Interestingly, cortisol travels to the brain and seems to reduce the sensitivity of the brain to the hormone leptin. As a reminder, leptin is the hormone that regulates body fatness. When your sensitivity to that hormone goes down, your appetite and your body fatness go up. Cortisol seems to dampen that signal. This has been demonstrated by some interesting studies by Eric Ravussin and others in both rodents and in humans. As it turns out, some people secrete a lot more cortisol than others in response to the same stressor. The people who secrete more cortisol are the same people who tend to overeat when they're stressed.

Dan Pardi - 23:20: Mm-hmm (affirmative), interesting.

Stephan Guyenet - 23:21: Yeah, so those people tend to overeat when they're stressed, and they also tend to gain fat in the abdominal area when they're stressed. Cortisol not only causes you to eat more and gain fat, it specifically causes that fat to accumulate around your abdominal region, which is the most dangerous place to gain fat. That's one important reason why researchers think stress can precipitate overeating in some people. There's another reason that's a little bit simpler, why we overeat when we're stressed, or at least why we eat less healthy food, and that's that certain types of food actually dampen the activity of the stress response system. Another way of saying this is very simple, is that comfort foods make us feel better when we're stressed.

Dan Pardi - 24:10: Right, it's like self-medication.

Stephan Guyenet - 24:11: Yeah, absolutely, self-medication. When we feel stressed, although not everyone overeats, most people do shift their eating habits toward calorie-dense comfort foods. These are generally tempting calorie-rich foods that are able to dampen the activity of that threat response system in the brain.

24:34: Animal experiments that were done by Yvonne Ulrich-Lai and others suggest interestingly that comfort is not the only thing that can do this. As a matter of fact, any type of reward can dampen the activity of the threat response system. Her research in rodents showed that that's particularly true for sex. It's kind of interesting. How do you give an animal, how do you give a rodent a natural reward that competes with food? There's really only one other one that competes with food, and that's sex. They showed that that helps dampen the activity of the stress response system, and I think that most people would intuitively agree that that's the case.

Dan Pardi - 25:17: Yeah. If you're feeling so stressed out that you're not really feeling like you're in the mood, get outside, go for a walk. Maybe find a combination of these rewarding natural behaviors that can then add onto one another to put you in a little bit of a better place.

25:31: One other comment around the overactivity of the amygdala and sleep, people that have PTSD, they have this overactive amygdala because of the experiences that they've been through. Sadly, that overactive response will activate vigilance centers in the brain stem, and then at the same time cause areas of the prefrontal cortex to decrease in activity that helps us generate sleep, so you develop insomnia. Everybody that has been stressed at some point in their life recognizes that their sleep is usually affected negatively, which then worsens the physiological stress that the body's experiencing, and promotes overeating.

Stephan Guyenet - 26:05: Yeah, absolutely. You probably know this well, with your strong background in sleep, but one of the primary outputs of the threat response system is to increase alertness and vigilance via those same circuits that regulate our sleep wake cycle.

Dan Pardi - 26:21: Yeah, which makes a lot of sense. If you're under threat, you need to be alert. If, for a variety of reasons, that alertness response is staying extra vigilant too much too often, that could be a problem. Another reason to maintain a good healthy lifestyle as best you can. Sunshine, walks, sex, all of it.

26:39: Kind of going back to in the beginning, we all live in this modern environment which you can really consider it fattening. Why do some people get fat while others don't? We're all in the same environment.

Stephan Guyenet - 26:50: Yeah, that's a really interesting question. I had to find a place in my book to discuss this because I think it's so important, and also underappreciated. I think appreciation of this is growing, but it's underappreciated. There are a large number of studies that have been done on the genetics of body fatness. What those studies show in aggregate is that differences in body fatness between people in society like the United States, or western Europe, or other affluent nations, those differences are accounted for about 70% by genetics and about 30% by environment. There's a very, very powerful influence of genetics on body fatness.

27:31: I think this meets typically with intuitive resistance from people. They say, "Well, if genetics are so important, then how come we're so much more heavier than our ancestors were? Don't we carry the same genes that they did?" Yes, that's absolutely correct. I think this points to a very important feature or limitation of these genetic studies, and that is that they apply specifically to the environment in which the data come from. Basically, if you're looking at a relatively homogenous environment like the modern United States, you're going to find that genetic differences account for most of the differences in body weight. If you were to compare two radically different environments like modern Americans to Hadza hunter gatherers, I think you would find that genetics explains very little of the difference.

28:19: The contribution of the environment depends on how that different that environment is between individuals. The more different the environment is, the more it's going to contribute to body weight. I think that offers hope, because it shows that environment actually does have a very powerful effect, but to get that effect, to benefit from it, you need to move significantly outside of the mainstream diet and lifestyle environment in our culture.

28:50: To dig a little bit more into that genetic data, there are these large scale so-called genome-wide association studies that try to figure out what are the specific genes that are contributing to these differences? There's a lot that we still don't know. We haven't explained most of it. From what we do know, most of the genes that we've identified relate to brain function, and many of them relate specifically to these brain circuits that I discuss at length in my book that regulate food intake and body weight.

29:21: Essentially, what it looks like is that the primary difference between people who are lean and people who are not is the genetic blueprint of how their brain is put together, which is pretty interesting. These genetic differences have been studied in greater detail than just their effects on body weight, and they've been shown to affect your appetite, your food preferences, your body composition, and they probably even affect your level of motivation to even care in the first place about diet and physical activity. People say, "Is motivation involved, is discipline involved in selecting your diet and in body weight and health?" I would say, "Yes, it's involved, but you have to remember that those things are genetically influenced, too.

30:06: You can't really change your genetics, unfortunately, but what you can do is you can do the best you can with the genetics that you have.

Dan Pardi - 30:14: Right, and I actually want to say something, because you mentioned that your book goes into the different circuits in the brain. If that's intimidating to anybody, don't let it be, because actually, going through one little part at a time, it shows you one very clear way one at a time that our eating is influenced. Overall, it doesn't feel like any sort of neurophysiology textbook, but rather it's like, "Okay, yeah, this is what's driving this way that I eat." It's all very relatable. As you understand that mechanism, you can really easily see like, "Oh, yeah, this is how I engage with food in this way." I thought there was lots of epiphanies and ahas reading it.

Stephan Guyenet - 30:49: Thanks, I appreciate that. I'm really glad to hear that, because my goal was really to write a book that would be accessible to a general audience. It's a tough line to walk between conveying science accurately and completely, and making it understandable to people who haven't been obsessing over this stuff for 15 years. I'm glad to hear that, and I've heard similar things from other people like my editor, who has no science background, found it understandable. I feel pretty confident that most people are going to find it accessible.

Dan Pardi - 31:21: You know, it's an extremely important book, because think about, yeah, this is condition, and these physiological factors and genetic factors are influencing how we eat, but even if you're not obese, and we have such an intimate relationship with food. What else are we putting into our body, except for air, multiple times a day for the rest of our life? Understanding some of these principles I think can just help you make better food choices, period. If you are dealing with wanting to lose some weight, what can we do to manage our own weight in this world that is really driving us to be fatter, almost from every angle?

Stephan Guyenet - 31:54: Yeah, so I think there are a number of things we can do. I'll touch on just a few of them today. The overarching principle that I use to think about this is that our eating behavior is driven in large part by these non-conscious brain circuits that I've been referring to throughout our conversation. These brain circuits are highly responsive to the cues they receive. They generate your instinctive responses to food and your instinctive motivations to food in response to the cues that they're receiving, both from your surroundings, your environment, as well as internal cues that your digestive tract is receiving from the food that you're eating.

32:38: If we want to manage our food intake and our body fatness in a constructive way, what makes the most sense from my perspective is to give those brain regions the right cues so that they are supporting your rational, conscious goals of eating the right amount and being lean, rather than fighting you and forcing you to exert willpower and cognitive control over these impulses that are leading you in the wrong direction.

Dan Pardi - 33:07: Right, right.

Stephan Guyenet - 33:08: Here are a few tips for giving those brain regions the right cues. I think one of the absolute most important things, and this is something I try to hammer in a lot of the interviews that I do, and that is controlling your food environment. Your ventral striatum, which is that motivational center that I was talking about earlier, and the things that it's connected to, too. It's not just the ventral striatum. Those things react to the cues that they receive.

33:37: If you have previously eaten ice cream, or pizza, or whatever, you have this reward association where once you experience cues that are associated with those things, such as the sight of those foods, or the smell of those foods, or locations of situations where you've had them before, those cues trigger your motivation. Your brain's basically saying, "Hey, I recognize this situation. This is the same situation I was in when I got a whole truckload of easily digestible calories last time. That was awesome, let's do that again." Even though your conscious brain doesn't think that's a good idea, those instinctive circuits aren't wired like that. They're wired to want that. They trigger your cravings and your motivations.

34:18: The key here is to not expose yourself to those cues that are going to fire up your motivational circuits. Especially thing that are visible or within arms reach, and that are calorie-rich and tempting, so like chips on the counter, cookies on the counter, soda. Foods that are very, very tempting, even if they're not visible, they can still hijack those parts of your brain, such as if you have ice cream in the freezer, or ice cream bars, or something like that. Just the knowledge that that's even there can cause you to crave those things.

34:51: If your brain isn't receiving those cues, not only is it just physically more difficult for you to get those things because they're not within close proximity of you, but you will actually crave them less. Over time, the less and less you expose your brain to those foods the more their power over you will dampen. Your brain forgets, or I think more accurately would be overwrites those associations over time, and they have less power over you the less you eat them. I think that's one way to do it that's helpful.

Dan Pardi - 35:22: I have a really good anecdote, because understanding some of these mechanisms myself, it was never so clear. I was thinking about the best dessert I ever had, and it's this place in San Francisco called Blue Plate. They had a crème fraîche vanilla ice cream sundae with homemade chocolate fudge and slow-roasted, 24 hour strawberries with almond slivers. It was the best thing I have ever tasted in my life.

Stephan Guyenet - 35:45: Wow. What effect did that have on you?

Dan Pardi - 35:47: Well, listen to this. A week later, I was thinking about how I could manipulate my wife so that when we were driving around the city that I could, including, "Okay, if we eat now at 11 o'clock, then by 4:00 p.m. or 5:00 p.m.," whatever, when I suggest, "Huh? What should we do for dinner tonight? Maybe we'll go back to Blue Plate," that she would be really receptive to it. I had strategized my entire day. I had been thinking about it day or day, and I strategized to try to have her say yes at the right time.

Stephan Guyenet - 36:20: Wow.

Dan Pardi - 36:21: I actually became conscious of that, and I was like, "Oh my gosh, this is really, really powerful." One other anecdote is, if you've ever had ice cream four nights in a row, its hold over you is never more powerful than that next night, when you've really ingrained that behavior. You've reinforced that behavior night after night, and you need it. You could be absolutely stuffed, and you really need to have ice cream. Then, if you don't eat it for a month, you don't think about it.

Stephan Guyenet - 36:43: Yeah, that's great point, and a great anecdote, as well. I have a informal rule with myself about alcohol where I generally don't drink it two nights in a row. That's for the exact same reason, because if I have it several nights in a row, then the night after, I'll feel like if I don't have it my evening just doesn't feel complete. That word association has just gotten stronger, but if I only have it every other night, then that doesn't really happen, I can take it or leave it. That's a much more constructive and comfortable place to be in.

Dan Pardi - 37:11: Totally.

Stephan Guyenet - 37:12: I've had similar experiences, and particularly with ice cream, I can still remember, just seared into my brain, the most delicious ice cream bar I've ever had. I got it at a convenience store. It was just on whim. I was with my wife, and we were checking out, and I was like, "Hey, those look good. Let's have one of those." I must have been hungry or something, because it was so good. To this day, everything about that, I remember the brand, I remember what it tasted like, I remember where I got it, I remember exactly where it was in the cooler. I don't remember that much about anything else in my life. I can hardly remember a few teachers that I had in high school, and I remember every detail about this ice cream bar that I ate once.

Dan Pardi - 37:50: Incredible. It just shows you that non-conscious processing, how that experience fueled dopamine, created that memory, and it ain't going away. It's a strong memory.

Stephan Guyenet - 38:01: Yup, yup.

Dan Pardi - 38:02: All right, this is an interesting question for you. The more you eat these hyper-palatable foods, the more that they leave this more indelible mark in your brain, and that can reinforce behaviors that put us in a challenging position inn terms of maintaining leanness, but at the same time, these sorts of pleasures are out there, and it's hard for people to say, "No, I just am never not going to eat that again." What's your calculation of that balance?

Stephan Guyenet - 38:24: Yeah, that's a really tough question. This is one that I've struggled with a lot, and we've both struggled with together on the ideal weight program. How do you strike the right balance? Because we have real lives. You don't really want to tell somebody, "If you go over to your friend's house, you can't have a cookie, or can't ever eat at a restaurant again." I think it depends on the individual. Some people do a lot better completely cutting things out. Some people can do moderation.

38:51: I guess for me, the most important way, again, is just to control your food environment. Don't have those things around at all, and you'll be a lot less likely to eat them in general. The less you eat them, the less power they will have over you over time. Just generally focusing your diet on simpler food, less highly palatable food, and not having those temptations around I think over time can guide people's habits in a more constructive direction.

Dan Pardi - 39:21: Yeah, and you know, you have to think about your life. Are you frequently dining out because of your work? That might be tough if you say, "I'm only going to have dessert occasionally if I do dine out," but then you're doing it all the time, versus not keeping stuff in the house. I found that replacing the really hyper-palatable foods with other stuff that's less palatable, more natural, that I really like is actually easy, because the focus isn't on not having something I like, but actually on having something I do like. Then, that's satisfying. That's been a pretty good one for me.

Stephan Guyenet - 39:49: Yeah, that's a good point, because I talk about this reward thing and the palatability thing a lot, and there has to be a balance. Most people, at least, those of us who are not monk-like, including myself, can't eat totally bland, unsatisfying food forever. Even though that may have some benefits for weight regulation, it's not really sustainable, so how do you strike that balance? I think a word that you used is very key here, and that is satisfying. There are foods that are very satisfying, like simply prepared meats, and pieces of fresh fruit, and unsalted nuts, roasted nuts, thing like that that are very satisfying but are not hyper-palatable in that way that hijack us into eating more calories that we need.

Dan Pardi - 40:33: That's a great point. It's so interesting to get into that loop with salt, like with chips, where you just don't seem to have a bottom to your stomach. The old saying with Lays, "You just can't have one," but that's a really true statement. Avoiding it altogether I think always feel better. I never feel good if I've ever gotten into that vicious cycle of, "I can't stop until the bag's done."

Stephan Guyenet - 40:53: Hm, yeah.

Dan Pardi - 40:54: All right, let's see. Controlling your environment, making sure that the food that you have in your surroundings is stuff that's good for you, and that you're also just not having ready to eat, palatable foods on the counter at any time, because that's going to drive you to eat even if you want to, and then you're eating the right food. Then, secondarily, healthy, satisfying, whole foods that you enjoy, but they're not promoting that overeating. Anything else?

Stephan Guyenet - 41:16: Yeah. We touched on aspects of this, but I think eating whole foods that, as we said, are satisfying but not excessively palatable and not too calorie dense is very important. There are a couple reasons for that. One of them is just what we were talking about, the reward value and the palatability of those foods, but another one is these signals that are coming up from your digestive tract. This is not something that we got into detail on here today, but when you ingest food, there are a lot of signals that are coming up from the digestive tract to the brain. Some of those are going to your ventral striatum and putting out dopamine, but there are also a lot of other signals that are going up to your brain stem and that are being integrated by your brain stem into a satiety signal.

42:01: As you continue to eat food, the properties of that food such as how much it's distending your stomach, and its carbohydrate, fat, sugar, protein content, etc, are all being detected, sent up to your brain stem. It's collecting all that information, and these are really complicated circuits. There's a lot of stuff going on in there, but all you're aware of is whether or not you are motivated to eat more food, in other words, whether you're full or not. That's kind of like the conscious output of this complex integration that's happening in your brain stem.

42:33: It turns out that certain food properties trigger that satiety response more than others per unit calorie. If you're eating whole, unrefined foods that are lower in calorie density, you're going to get more satiety per calorie than if you're eating very calorie-dense, refined, and highly palatable foods. I think that's another way to send slimming signals to the non-conscious circuits in your brain that regulate your calorie intake.

Dan Pardi - 43:02: Yeah. At this point, we would be remiss not to mention the ideal weight program, which is the weight loss and weight maintenance program that we've put together. Why don't you do us the favor, tell us a little bit about what that program is.

Stephan Guyenet - 43:12: Yeah, sure. I'm really excited. We're on the final stretch here of putting together a whole new version of it. It's going to be a huge upgrade. It's super exciting. This is integrated with the HumanOS platform that Dan's been working on that's really cool. Basically, it's going to be a course-based system now. The new one's going to be a course-based system. There are a series of courses that are designed to educate users about six core determinants of eating behavior and body fatness, and how to use those to your advantage.

43:46: Basically, we've sifted through enormous amounts of scientific evidence and tried to really drill down on the core strategies that are going to be the most sustainable ways to regulate your weight. A lot of the ideas are similar to our previous version of the ideal weight program, but they're just presented in a way that's a lot more engaging, and a lot more thorough, and a lot more clear.

Dan Pardi - 44:10: Yeah, I'll add, the whole course platform is really meant to help people develop fluency on a subject, because you might be listening to this podcast, recognize a lot of what we've discussed, but can you discuss it with your friends? Are you that fluent in that information? I think that's really important. The way that we present the new info does it so that you can retain this information better. The better you can speak to it, the better you can live it.

44:33: Yeah, I'm really proud of it as well. By the way, I think that the book and the program dovetail perfectly with each other, because the book goes into more detail, it's more of a narrative around a lot of these different concepts, and then the courses really drill down to the main points that help you implement it in your life. Together I think you can develop skills that can last for the rest of your life that can keep you lean or leaner.

44:54: It's a enormously huge problem in our society, and that's if we look at the societal level, but for an individual, it can cause people a lot of frustration and confusion, like, "What do I do?" There's a lot of different ideas. Hopefully this will help a lot more people. I know I'm getting letters from people on a regular basis that it's helped a lot, so that always makes me feel really good.

Stephan Guyenet - 45:12: Awesome.

Dan Pardi - 45:12: Well, Stephan, congratulations on this enormous undertaking. It's a really great book. It's easy to read, it's fun to read. Every chapter has those epiphanies, like I said, where you have those aha moments that help you see the world you live in slightly differently, because now you understand the science around it. I really do encourage everybody to go out, pick it up, and I appreciate your time today.

Stephan Guyenet - 45:30: Thanks very much, Dan. Good to be on the show.

Dan Pardi - 45:32: We'll have to have you back. I'm going to twist your arm again to come back in the future. All right, have a good one.

Stephan Guyenet - 45:37: All right, you too.

Kendall Kendrick - 45:40: Thanks for listening, and come visit us soon at humanos.me.