Why is it that both low-carb and low-fat diets can produce weight loss? Why is it so hard to avoid foods that taste good? Is it really about willpower? Today I discuss the brain’s influence on food intake with neuroscientist Dr. Stephan Guyenet. Learn why our brain is hardwired to seek out calorie-dense foods and discover four strategies for “tricking” the brain and achieving sustained weight loss.
In this episode we cover these topics:
- Why it’s the brain that controls obesity
- The ancestral perspective on food intake
- Is it really about “calories in/calories out”?
- Why both low-fat and low-carb diets reduce calorie intake
- Are carbs and sugar to blame for obesity?
- Does dietary fat cause obesity?
- How to work with your brain to lose weight
- The Hungry Brain: Outsmarting the Instincts That Make Us Overeat, by Stephan Guyenet
Chris Kresser: Hey, everybody, Chris Kresser here. Welcome to another episode of Revolution Health Radio. Today, I’m going to interview Dr. Stephan Guyenet about his fantastic new book, The Hungry Brain. You may recognize Stephan as a previous guest on the podcast. He is actually the only guest, now with this third visit, who has been on my show three times. He was one of the first guests I ever had way back when I started Revolution Health Radio, which was not called Revolutionary Health Radio at that point. I think it was called the Healthy Skeptic Podcast … I don’t even remember, it was a while ago. But the reason I’ve had Stephan on twice and now this third time is that I really consider him to be one of the most informed and sanest voices in the discussion about why we gain weight and why it’s so hard to lose it.
Stephan has been a neuroscientist for 12 years. He worked in a lab that studied the neurobiology of fat regulation for four of those years and is just an extremely insightful, bright, and level-headed scientist, researcher, and commentator. I appreciate his perspective on these topics, and I think his new book is by far the best publicly available resource now that explains the evidence behind weight regulation, and so I’m happy to welcome Stephan back. We’re going to talk about some of the key concepts from his book and then some of the biggest myths about fat loss, and I hope you get a lot out of this and enjoy it as much as I did. Okay. Let’s dive in.
Chris Kresser: Stephan, welcome back. I have to say you have the distinction of being the only guest that’s ever been on my podcast three times. How does it feel?
Stephan Guyenet: It feels great. Thanks for having me back again, Chris.
Chris: It’s a pleasure. I love having you on the show because when I think of someone that has a real evidence-based, fact-informed perspective on weight regulation—why we gain weight and why it’s so hard to lose it and how we can actually lose it—you’re the first person that comes to mind. There’s so much misinformation, I think, out there about this topic and it drives me absolutely nuts. I know you’re right there with me a lot of the time.
Stephan: Yes, I am.
Why it’s the brain that controls obesity
Chris: On that note, you tell us, why did you feel compelled to write this book? I mean, there are many other ways you could spend your time, and I know firsthand that writing a book is an arduous process. What was your overarching goal here?
Stephan: I spent 12 years in the neuroscience research world of food intake obesity. First of all, there are a lot of different things that you can study in this world, that you can research in this world. And the one that I started off studying in graduate school was very interesting, but it was a disorder that was not very common. I decided I wanted to move into something that was more common and more impactful, which is obesity. I think that’s one of the more impactful conditions in this world in terms of reducing quality of life and promoting disease and those sorts of things. I started my postdoctoral research. I switched from studying a rare neurodegenerative disease to studying food intake and obesity.
And during the course of my research, it really dawned upon me very, very clearly that the brain is really the organ you want to be thinking about if you’re thinking about food intake regulation, body weight regulation, and body fatness. It’s really not difficult to demonstrate that. It’s really just kind of common sense if you think about it. It doesn’t really take research to realize this, but the brain generates all behaviors, including what you choose to eat, how much you choose to eat, and how you use your body, and it regulates a lot of the physiology of your body as well. What’s going in and out of your liver, what’s going in and out of your muscles, what’s going in and out of your fat tissue, how fuel is being burned—those things are all influenced by the brain. It’s very much kind of the obvious place to look.
Four strategies to avoid the “hungry brain” and lose weight
But what I realized over the course of my research, over the course of writing on my blog is that that wasn’t really a common perspective. It wasn’t really a common angle to see the problem from, and I understand. I mean, the brain is complicated, and I think our understanding of it has been growing very rapidly. I think until recently, maybe, we really didn’t have what it took to see food intake regulation and body weight from the perspective of the brain, but we do now, and so all of that together convinced me, plus the fact that there was no general-audience book that kind of took a broad look to my knowledge. I have not encountered another general-audience book that took a broad look at the role of the brain in food intake and body fatness, so that seemed like a pretty immense gap in the general audience literature and something that I felt was very useful to educate people about, and I felt that I was in the right place to do it, and so three years ago I embarked on this project.
Chris: Well, I’m so glad you did, and I just want to kind of stop and reiterate what you said, which is that once you start studying obesity in earnest, you quickly come to the conclusion that the brain is running the show and yet—I almost interrupted you because I was … you mentioned how obvious that is—and yet it’s really not been the driving factor in the discussion around obesity and weight regulation. It’s all of the downstream effects of the brain’s influence on behaviors or physiology related to food intake that you mentioned, like the insulin and fat cells and all of this stuff. That’s really what people have been talking about for the past couple of decades in the popular media. It may be that researchers have been focused on the brain, but it seems to me as a clinician that most of what we’ve heard is all of this argument and debate about, you know, insulin and these downstream effects, and I really think that this is going to be a revelation for a lot of people when they read this book—these obvious things that are overlooked that can be so powerful.
Stephan: Yes. That’s a good good point. I think that you can you can look at eating behavior and body fat from a variety of different angles. I don’t want to say that the brain is the only valid way to look at it. But at the same time, I think that if you really want to understand the source and you want to fundamentally understand what’s going on, that understanding has to include an understanding of the brain.
Chris: Yes. I would say also along the same lines that if you only look at the other things without understanding the brain, you’re missing some really critical information. I mean, just speaking again as a clinician, I think when I have explained some of these concepts that I originally learned from you, like the body fat, adipostat—the body fat thermostat, so to speak—the hedonic homeostatic dysregulation/regulation of weight, and some of the stuff that we might talk a little bit about today and we’ve talked about on our previous podcast, it really turned the light on for some of these patients because it helped them understand how they could continue to have trouble losing weight even when they’re doing the so-called “right things,” like, “Hey, I switched to a low-carb diet and I’m still not losing weight. Why is that?” Any number of changes they could have made that were in theory supposed to work based on whatever idea that they were following didn’t actually work, and understanding the brain and the brain’s role helped them to get their head around that and actually to make some changes that ended up being more effective in terms of weight loss. I think it’s not just important from a scientific perspective, it really actually translates into useful information for people who are trying to lose weight and for clinicians, coaches, anyone who’s working with people to lose weight.
Stephan: Well, I’m really glad to hear that it’s been useful in that way. One of my hopes for this book is that as people read it that light bulbs will go off and they’ll say, “Wow! This actually really explains my experience quite well.” It’s my belief that that will happen for many people because the whole idea of the book is understanding these non-conscious impulses that drive us to eat more than we think we should. If you’re able to describe those impulses and where they come from, then it’s like, “Oh, hey, that’s why I behave like that even though I know it’s not really good for me.”
The ancestral perspective on food intake
Chris: Right. And we’ve talked about that in many other contexts with the ancestral perspective, like understanding the influence of our genes, thousands of generations of evolution on our behavior. I think for a lot of people listening to this, it won’t come as a surprise that we have hardwired genetic mechanisms that influence our food intake in a way that’s not easily controllable by our conscious mind. I mean, there are certainly things we can do, which I want to ask you about, consciously to mitigate some of those hardwired tendencies, but they were really kind of something I’ve taken away from understanding a lot of the things we’ve talked about is we’re really kind of fighting against some deeply, deeply entrenched kind of behavioral tendencies that aren’t easy to overcome.
Stephan: Yes. That’s exactly right. There’s a reason why our impulses work the way they do, and the reason is generally that they were things that supported the survival of our ancestors. Energy is so critical to survival. Calories are so critical to survival and reproduction, and so the brain is wired very deeply and very powerfully to behave in certain ways with respect to energy, and those ways make a whole lot of sense in the context of our distant ancestors but not so much today.
Chris: Right. And so, an environment where food scarcity was the biggest problem, they gave us a survival advantage. But in this current environment where you can walk down to a 7-Eleven and get a 72-ounce Big Gulp and Twinkies on virtually every corner, it’s a prescription for obesity.
Stephan: Yes, that’s right. It’s kind of funny because there are kind of analogous situations to 72-ounce Slurpees in hunter–gatherer scenarios, like, for example, Kim Hill, who’s one of the anthropologists I interviewed for my book. He told me that Aché hunter–gatherers and the Hadza of Tanzania do similar stuff. They will sit there and eat a quart of honey like, a liter of honey just straight.
Chris: That’s insane.
Stephan: I know, isn’t it? I mean, it’s hard to even imagine doing that. But they do the most outrageously gluttonous things and they don’t have the same inhibitions that we do. For them, that’s a good thing. To do that is a good thing that you want to do, and there’s no reason not to do it because you need …
Chris: They’re not going off into the jungle and throwing up after that or doing some of the things that we’ve been trained to do out of shame, you know, for caving into those hardwired mechanisms.
Stephan: Right. They’re not feeling guilty. There’s no reason to be to be guilty because it’s a good thing. But the reality is that, that doesn’t happen every day and it doesn’t happen every other day. They often get honey but they can’t usually get enough of it to exceed their calorie needs. Overall they’re really, like, fighting to get enough calories, and part of that struggle is to gorge when you have the possibility of gorging when the opportunity perfectly presents itself. Our brains are kind of wired like that. Most of us don’t gorge to that extent, but I think those same instincts push us a little further than we really want to go.
Chris: Yes. And you don’t have to look back that far even to see some of this. My wife is Canadian, she’s from British Columbia, but one side of her family is from Saskatchewan, which corresponds to the Midwest of the U.S., and they’re farmers. She told me that she has memories when she was a little girl going to visit them in Saskatchewan and her grandmother or great grandmother perhaps would set down this huge plate of food in front of her, and when my wife would say, “I’m not hungry anymore,” her grandma would say, “Eat for the hunger to come.” There’s this idea that there might be a famine next season so you better eat out now while you can. This is just two generations ago.
Stephan: Yes. That’s amazing and you see this tradition in a lot of different cultures. You see this in Eastern Europe, in Western Europe, even in older folks, and like you said, in traditional families in Canada and the U.S. that there is this culture of trying to eat as much as you can because it’s actually good for you in a certain context. But yes, we obviously don’t live in that context anymore.
Is it really about “calories in/calories out”?
Chris: Okay. I want to switch gears and talk about some of what I think are the biggest myths about weight regulation, some of which we’ve discussed on the show before and you talk about in your book, but let’s talk about calories first. If we think of it like a spectrum, maybe on one end there is the argument that calories don’t matter at all and it’s just the type of foods you eat that determine whether you get fat or don’t get fat, and then on the other end of the spectrum, it’s all about calories 100 percent. And I know this is a little bit of a straw man, so we can address that, but let’s dive into that. Where do you fall on that spectrum, and, you know, what would you say about that?
Stephan: Just to define the question a little bit more, I think that there’s a whole causal chain leading from food to excess body fatness, and I guess the question is, are calories in an essential part of that causal chain? I would say that yes, they are, and so if we had, like, a scale of 1 to 10 of “1 is calories are totally irrelevant” and “10 is calories or everything in terms of body fatness,” I would say I’m around like 8 or 9, plus or minus 1. I think that there’s very good evidence. As of right now, the evidence suggests that calories are the only known food property that has any impact on body fatness at all. That doesn’t necessarily mean that there are no food properties that can impact body fatness independently of calories, but that’s the only thing we have evidence for, and there have been a number of studies on it at this point.
There was a paper that came out just a few days ago, I think, where they were looking at the impact of refined grains versus whole grains and they showed that the same number of calories—I haven’t looked at the paper, I don’t know how solid it is, I just saw the abstract—but they were suggesting that when you eat whole grains, there’s some small portion of those calories that get excreted, and it may also increase your energy expenditure slightly such that there’s a small effect on your energy outside of the equation that’s independent of the number of calories in your food. There could be effects like that that have a small effect, but I think to a pretty close approximation, calories are the only food property that affects your body fatness. I think that, I don’t want to say that there’s absolutely nothing else that ever affects it, but I think to a pretty close approximation, that’s the case.
Chris: I kind of set you up with that question, so I’m glad you redefined it. The other thing that I think we should point out is that the fact that calories play a major role in weight gain or fat gain doesn’t necessarily mean that restricting voluntary calorie intake is the best way to lose weight, or does it?
Stephan: Yes absolutely. I think this is exactly …
Chris: People conflate those two things together, and they think that if you accept one, you have to accept the other, but that’s not necessarily true.
Stephan: Yes. That’s absolutely right. And this is why when people ask me if I believe in “calories in, calories out,” I ask them what they mean by that because, like you said, it can mean two different things. Either that the balance between calories in and calories out is the thing that affects body fatness or that voluntary decisions about how many calories to eat are the only way to regulate body fatness. And yes, like you said, one can be true without the other being true, and I think that if you look at studies where they’re just using portion control and calorie control where people are simply told to eat fewer calories to lose weight, what you see is that that approach doesn’t work that well—if you stick to it you will lose fat.
There’s no question that restricting calories causes fat loss, but the problem is that that’s not the natural way that we interact with food. The natural way that we interact with food is we eat when we’re hungry or tempted, and then we stop when we’re full. We’re not regulating it really on this conscious, rational, spreadsheet level; we’re regulating it on an intuitive level. I think even though the number of calories that you eat has a very powerful impact on your body fatness, regulating the number of calories by changing those, by trying to have a direct impact on those impulses is a better way than actually trying to count calories. For example, just to give you an example to make it a little more concrete, eating food that has a lower calorie density and higher protein so that you feel more full per unit calorie, so you, when you hit that point where you intuitively want to stop eating at a point where you are eating fewer calories. That doesn’t require calorie counting, but it does have the effect of reducing your calorie intake.
Chris: Right. That would be an example of involuntary calorie restriction, where, putting it in layperson’s terms, you naturally eat less without trying to by virtue of what foods you’re eating.
Stephan: Absolutely. It’s a phenomenon that you see when you put people on a variety of different diets, including low-carbohydrate diets. You don’t have to invoke any kind of metabolic magic to explain why people lose fat on a low-carbohydrate diet. They spontaneously start eating fewer calories, so the effect is very consistent with the known impact of calorie intake on body fatness.
Why both low-fat and low-carb diets reduce calorie intake
Chris: Let’s talk a little bit about why that happens with macronutrient restriction. You have a section in your book, the United States of Food Reward, where you go into a lot more detail about this, but let’s just touch briefly on that, on why someone would naturally eat fewer calories on a very-low-carb diet or even a very-low-fat diet.
Stephan: Yes. I think there are a couple of different reasons, but I do think there is a very important observation that you just made there in passing, and that is that you can see reductions in calorie intake and body fatness on diametrically opposed diets. Low-carbohydrate diets cause that, and low-fat diets also cause that even though the macronutrient they’re restricting is the opposite one. By the way, it is true that low-carbohydrate diets tend to cause more fat loss. Nevertheless, low-fat diets do cause fat loss. That’s not really consistent with the hypothesis that one macronutrient is fattening and the other one is slimming, and if we just cut out the fattening one, we’re going to lose weight.
So, how do you explain that? How do you get to a higher-level, overarching principle that can explain both of those things? So, there were a couple of them, and one of them that I’ll start with is the reward value or the seductiveness of the diet. The human brain is literally hardwired to look for certain properties in food, and these include starch, sugar, fat, and protein. There are literally sensors in your small intestine as well as in your mouth, of course, that detect the chemical properties and the volume of what you’ve eaten and send all that stuff back up to the brain. If your brain gets the message that the food is an outstanding source of fat, carbs, and protein, you get some dopamine spiking, and then you’re going to be highly motivated to eat that food next time. The smell of it, the sight of it, and all that is going to be really motivating and seductive for you. It’s going to trigger that motivation. If the brain decides (based on the physical properties of that food that it’s measured) that it is an exceptionally valuable food because it has large quantities of all these things at once, it has a way of kind of sweeping aside your natural limits on intake, reducing the satiety mechanisms, and increasing your body fat set point to kind of facilitate intake of that food that it views as so valuable. But if you present a diet that’s lacking—or at least substantially reduced—in one of those reward factors, one of the main things the brain is looking for, it’s just not quite as interested in eating as much of that food. It’s not going to quite drive that eating behavior to the same degree because that food doesn’t have all of that wonderful stuff that it wants. It’s got some of it but not all of it.
Chris: And again, it’s in an environment of food scarcity where getting all of that good stuff would help you survive a period of famine and be healthier and procreate more successfully, then that’s great. But when you’re talking about the difference between eating a steamed baked potato with no butter or salt, or a full bag of potato chips, it may not be the best genetic programming.
Stephan: Yes, absolutely, absolutely. And just to complete my thoughts a little bit, low-carbohydrate diets also tend to have a higher proportion of protein. I’m not talking about the very-low-carbohydrate ketogenic diets necessarily, but just your standard moderate-low-carb diet tends to have a higher proportion of protein. That also tends to feed back on those brain circuits and tells you to eat less.
Chris: Right. This is, again, I think another point of confusion where people see reports on the research of where a low-carb diet was effective, and they automatically assume that that was because of the removal of carbohydrate, which, as you’ve just explained, it’s not necessarily a safe assumption, and in fact there’s plenty of research that I’ve seen as well that suggests that it may be more related to the increase in protein intake than it is the restriction of carbohydrate.
Stephan: Yes, that’s right. I wouldn’t say it’s necessarily 100 percent definitive yet, but that is what the research is suggesting, I agree.
Are carbs and sugar to blame for obesity?
Chris: Well, that’s a good segue to the next myth about weight regulation, and this one we’ll will start with the more contemporary version of this. The next two are related to macronutrients. But lately, it’s been more the idea that carbs are to blame for the obesity epidemic, and in particular, as people like Gary Taubes have argued in his recent book, most explicitly that sugar, especially refined sugar, is to blame for the obesity epidemic. Let’s tackle both of those, starting with just carbohydrates overall as the micronutrient and then moving onto sugar specifically.
Stephan: Yes, sure. I think the starting point for this is to look at non-industrial cultures. I think it’s not the only part of the picture but it’s the one part of the picture, and what we see if we look at non-industrial cultures is that there’s a very wide spectrum of macronutrient intakes historically and most of the non-industrial cultures that we have evidence from were actually eating a very-high-carbohydrate, lower-fat diet. There were also some that were eating high-fat, low-carbohydrate diets, and really none of them had the diseases we’re trying to avoid today. It’s obviously possible to eat those kinds of diets in the context of unrefined food and physical activity and a healthy lifestyle, It’s obviously possible to be lean, and it’s possible for entire cultures to be lean and healthy on almost any macronutrient makeup.
I guess I don’t even really understand where this idea comes from because there’s not really any research that suggests that carbohydrate is disproportionately to blame for obesity. If you put people on high-carbohydrate diets, they don’t gain weight. They don’t become diabetic. It doesn’t happen in animal models. It doesn’t happen in people. There’s no association in observational studies between total carbohydrate intake and obesity or diabetes or any of that. What you do see, you see that refined carbohydrates and sugar are associated with poor health outcomes, and that’s, I think, just consistent with the general idea that if you eat a refined, calorie-dense diet, you’re going to tend to have poorer health outcomes. But that’s true in general. It’s not just, it’s not just refined carbohydrates, it’s refined anything.
Chris: I don’t want to go too far off on this tangent but it is kind of an interesting question to think about where this comes from. My sense is, like you said, there is some research to suggest that excess intake of refined carbohydrates can lead to increased consumption of calories that isn’t compensated for elsewhere, which we understand. What we’ve been discussing so far, that calorie intake does matter, then, yes, refined carbohydrate would contribute, but then somehow that gets extended to all carbohydrates. I don’t know. It’s interesting to think about if we’re talking about evolutionary mechanisms. You and I traded some emails about this tendency for kind of black-or-white thinking in human beings and that maybe that itself has some genetic roots.
Stephan: Yes. I think, I think people want simple heuristics. I don’t think the average person wants to have to study health and nutrition deeply to understand what to put in his cart at the grocery store. We tend to come up with these simple heuristics, like fat is bad or sugar is bad, and if I just avoid that then I’m cool. Unfortunately, human biology and the way that we interact with food is just a lot more complicated than that. I think that people, they look for simple solutions, and simple solutions are not necessarily the most accurate.
I think for sugar—just to get into the sugar thing a little bit—I personally have little doubt that sugar is involved in obesity and chronic disease. But I think to claim that it’s the primary factor, you have to overlook so much evidence that other things matter that it’s mind boggling.
Chris: Right. I think this goes without saying, but you’re not advocating that people eat sugar or suggesting that sugar doesn’t play a role in obesity or play a role in other health problems. I know you and I know what you eat and know that sugar is not a significant part of your diet. I know you don’t work for the sugar lobby. For the record, that’s not what you’re saying. You’re just saying that if you if you look at the evidence in a dispassionate way, it’s extremely difficult to make an argument that sugar is responsible for the obesity epidemic.
Stephan: Entirely responsible, yes. It really is. It’s just hard for me to understand. I read Gary Taubes’ book The Case Against Sugar. I know all the evidence that’s cited and I just do not understand how this adds up to any kind of cohesive, compelling argument that sugar is the only thing that matters. It kind of blows my mind that these arguments are all over the media right now and that people are taking this seriously. It’s an incredibly weak argument.
Chris: Yes. Well, we could go in a lot of directions with the media and their capacity for nuance, but let’s not do that. Let’s just agree that the media is not renowned for its capacity to handle nuance, and some very sophisticated arguments when we’re together, whether we’re talking about politics or nutrition science. I think the media suffers from the same issue that you talked about with individuals, where it’s much rather it just be a simple, easy, attractive headline to say “sugar is the enemy,” and all you need to do is cut sugar out of your diet, and then you won’t have to worry about weight gain. That headline’s going to get clicked on a lot more them than one about the way that the brain regulates weight, unfortunately. Sorry if that’s news to you, Stephan!
Stephan: Newsflash: simple arguments get clicked on more on the internet.
Does dietary fat cause obesity?
Chris: Right, yes, simple and often wrong arguments. Whether they’re supported by any shred of evidence doesn’t even come into the equation, especially nowadays. Okay, so let’s turn that around because prior to the last couple of decades and especially the last decade, the opposite argument was often advanced, which is fat, it was solely to blame for the obesity epidemic and also the epidemics of cardiovascular disease and diabetes, which led to the whole American Heart Association, American Diabetic Association recommendation for a very low-fat diet in the first place. Is that, is that true, or is it the same problem with the carb idea?
Stephan: Well, I want to start off by acknowledging that this argument (that was made especially in the ’70s through the ’90s … I mean, it hasn’t disappeared, but it was most prevalent then) had an evidence basis. If you give animals, for example, a high-fat diet, they will tend to gain weight, and if you give them a low-fat diet, they will tend not to gain weight. They did studies in humans, short-term studies kind of confirming that if you loaded the diet with fatty foods, people would eat more and gain body fat. It’s not like it wasn’t based on anything. I think it’s often portrayed as kind of this nonsense that never had any rational basis, but there was evidence there and there continues to be. But I think there was a lack of nuance that is very similar, I think, to what we’re seeing now with arguments about sugar. Except that at that time it was coming from the scientific and public health communities. It was a lot more kind of respectable.
Stephan: The idea was that fat is fattening, and if we eat less fat, we will lose body fat. And that was tested in some big, giant, expensive, long, randomized controlled trials and shown to not really be as accurate, as correct, as people thought it was. There were caveats interpreting these studies. But at this point we have a lot of evidence from randomized controlled trials on low-fat diets, and we can say that at least the form that’s typically practiced, which is like a moderate-low-fat diet, is not really that effective for any of the things that we want to do, which is controlling obesity and diabetes risk and stuff like that.
I think we have enough evidence at this point to say that that model was not quite correct, and I think the way to reconcile all of the evidence for me is again to pull back from the macronutrient focus and to focus on these higher-level properties of calorie density and food reward or the seductiveness of food and whether food is refined or not. I think those are the higher-level properties that determine to a large extent whether a diet is going to be slimming or fattening, no matter what its macronutrient content is.
How to work with your brain and lose weight
Chris: Right. Why don’t we talk about that? If we’re saying it’s not necessarily counting calories that is the best approach, restricting macronutrients may help but not necessarily the way that you think it does, cutting out carbs doesn’t necessarily help because carbs aren’t bad and fattening, and same is true for fat. You mentioned three kind of top-line ideas or premises that you talk about in much more detail in your book, but let’s just review those. For someone who wants to lose weight, you’ve mentioned calorie density (I’d like you to define that, and, you know, use a few examples) and you’ve mentioned the reward value. We talked about the palatability of food, which we’ve discussed before, but I’d like to go over it again for people that haven’t heard those shows. And really, just like if you were to explain these concepts to someone who wasn’t familiar with them at all, what would be the three things to focus on for someone who is concerned with weight gain or weight loss?
1) Avoid foods with high calorie density
Stephan: Sure. As you said, I talk about a number of different things in my book, and I think more than we have time to cover today, but I’ll cover three things that I think are important. The first one is the calorie density, you mentioned that. Calorie density is the number of calories per unit weight of food, and I think a better way to think about it is per unit volume, even though it’s usually measured as weight in the scientific literature because volume is really the thing that matters. You have sensors in your stomach that literally … they’re stretch sensors, and they literally detect the volume of food that you’ve eaten and they send a signal up into your brain, and that’s one of the things that’s integrated into your feeling of fullness or satiety. If you eat a food, if you eat a meal that’s lower in calorie density, you’re going to hit that fullness point, that satiety point, after you’ve eaten fewer calories than if you’re eating very, very calorie-dense foods. Things like baked goods, like pastries, cookies, white bread, and other calorie-dense things like potato chips and candy, those things are some of the least filling foods per unit calorie, which means that you have to eat more calories until you hit that point that says, “Hey, I’ve had enough and I’m comfortable not eating.” Stuff like pizza too.
Stephan: I think that’s a very important concept, and I think if you look at the animal research literature too, what you see is that it’s not so much, it’s not really so much the fat or carbohydrate content of the diet that matters. You can put that into rodent chow and they will eat more and they will gain fat. But the thing is, added fat like we use in those experiments is very calorie dense, and if you give them a diet that has a higher proportion of calories from fat but that is not as calorie dense—so you kind of water it down with some fiber or something—what you find is that it doesn’t have that same fattening effect. It’s not really the fat per se; it’s that calorie density that is affecting their food intake and their body fatness. That’s one thing that I think is a very important concept. There are other things that go into how filling a food is per unit calorie, such as the amount of fiber it has and the amount of protein. Both of those increase the fullness per calorie.
2) Avoid foods with high reward value
Stephan: Another property is the food reward value, and I call this seductiveness. I think that’s kind of an intuitive way of explaining what it is. It’s the motivational value of the food and the pleasure value. It’s that craving that you feel when you see that food like ice cream, pizza, or whatever. That’s the reward value.
Chris: You explained reward to me on an earlier show in a psychological context, the formal definition of something that makes you want to do more of it, which I thought was useful to understand.
Stephan: Yes. That’s absolutely right. That’s a core property of reward is that it causes you to repeat your behavior and to strengthen your behavior. It basically drives your motivation, your craving for that thing. This is true in many areas of life. It’s true for gambling, it’s true for videogames, it’s true for a lot of stuff, but food is a very powerful reward, and so it applies very strongly to that. Foods with certain properties have a higher reward value. Foods that essentially are giving the brain what it is instinctively looking for, which is very high calorie density, fat content, sugar, salt, and to some extent protein, and especially glutamate, which is that umami, that meaty, umami flavor which is a part of cooked meats and other things.
The converse of those highly seductive, highly palatable foods like ice cream and pizza is simple, whole foods like the ones that our ancestors used to eat. Things like tubers that are just baked, and pieces of meat that are cooked simply—raw fruit, vegetables, and nuts, just roasted nuts with no salt on them, and things like that. Those are just plain simple foods, so that’s kind of the flipside. And if you eat those kinds of foods, the effect that it has on your brain is one of, first of all, helping you feel satisfied with fewer calories, and second of all actually helping your brain to feel more comfortable at a lower level of body fat. When you lose weight your brain is not going to trigger that same starvation response to the same degree as it would if you were just cutting back calories on your normal diet.
Chris: That’s interesting. That’s something we didn’t discuss in detail before, but a very important point.
Chris: This experience also, I mean, you’ve written about this. There’s an entire book about this, the title of which I’m forgetting, I’m sure you know it, where these concepts are not foreign to big food, the companies that manufacture processed food. There’s that famous Pringles advertisement that when people of our generation were growing up, I bet you can’t just eat one, and that’s a bet that they knew they would win, right? Because they employ food scientists that have engineered those chips to trigger all of those reward mechanisms in our brain and make it very, very difficult for us to just eat one versus if you compare, you know, a baked potato, as we said earlier, that’s just steamed or baked with no salt or butter, it would be quite hard to overeat that, wouldn’t it, because in that situation you’re just going to eat what you’re hungry for and probably not much more.
Stephan: Yes. That’s right, and you actually will feel no desire to eat any more unless you have something more tempting or something different in front of you, but that’s absolutely true. The food industry very explicitly designs its foods to trigger our known motivational circuits because that is what makes them money. When our motivational circuits are triggered, we pull out our wallets and we purchase their food. That’s explicitly the goal of designing the food how they design it, but I will say that the same thing happens in our kitchens to a lesser extent. We try to make the food taste as good as we can, and so everybody is kind of jockeying to satisfy the innate food preferences of the human brain. But I think that the food industry is just particularly good at it.
Chris: Most people for a dinner party aren’t going to serve baked potatoes with no butter or salt.
Stephan: Well, you’ve never been to one of my dinner parties.
Chris: Oh, actually, I was going to say most people except you. But I have been to one of your dinner parties, and it was quite good actually. But you probably wouldn’t have too many people coming back to your dinner party after that. We only have a few more minutes, but I want to at least touch on one significant non-food mechanism that contributes to weight gain. Well, let me see if you agree with this. The primary influence on weight is food intake and not exercise, stress, or something that’s, you know, non-food related. A) Would you agree with that? And then B) Even if you do agree with that, when you think of other non-food influences, which ones are the most significant, you think?
Stephan: A: I do agree with that. I think that there’s pretty good evidence that food intake in humans, for most people, is the predominant influence on by fatness. If you look at the studies that identify how the brain regulates body fatness, like the responses it initiates to try to regain fat after a person loses fat, what you see is that those are primarily concerned with increasing calorie intake and to a much lesser extent with decreasing calorie expenditure. The brain really regulates your body fat and it’s primarily by trying to modify your food intake. I think that’s really the number one point of leverage for someone who is trying to regulate their body weight. Again, I’m not trying to say that nothing else is important and I’m not trying to say that that is always going to be the best lever for every individual, but I think in general and on average, that’s going to be the most powerful lever for most people.
3) Pay attention to sleep and circadian rhythm
Stephan: To think of something else that affects weight, there are a couple of different non-food things that affect the weight, but I’ll focus on one that I’ve talked about in my book, and that is sleep and the circadian rhythm. There’s pretty good evidence from short-term randomized controlled trials that if you restrict a person’s sleep, they will eat more calories, and they actually may burn a few more calories as well because you burn fewer calories when you’re asleep and more when you’re awake. But it doesn’t make up for the higher intake. People actually will eat 300 more calories a day which is pretty substantial. If you were to sustain that, that’s the difference between a person who’s lean and a person who’s overweight in terms of calorie intake, that’s pretty substantial. And then you could ask the question, “Well, does that persist in the long run? Do we really see that that actually makes people gain weight or does it kind of go away after a while?” And what you see from the long-term observational studies is that there’s actually a pretty strong association between insufficient sleep and weight gain over time. I think together that paints a pretty consistent picture that not sleeping enough does probably promote weight gain over time.
Interestingly, it probably operates primarily through changes in food intake, and there are a couple of different reasons for that. When you put someone in an FMRI, this is a machine that can detect brain activity, so you’re looking at their brain activity—if they haven’t slept enough, their brain kind of acts like they’re starving. All those same responses that you see in the brain of someone who has just gone on a diet and their brain is activating that starvation response, they’re feeling hungry or they’re feeling more tempted by food, maybe they’re feeling a little bit sluggish and cold, those same responses or at least very similar ones occur in the brains of people who are sleep restricted. It activates some of these same circuits that cause us to be more seduced by food and require more food to feel full. That’s one way it can work.
The other way it can work is that … so, sleep restriction, it’s really bad. It does a lot of really bad things to your brain. One of the things it does is it seems to impair your ability to make good judgments and so you develop what’s called an optimism bias where you’re not very sensitive to the downsides of making a decision and you’re paying more attention to the potential upsides relative to what you would do if you were well-rested, and how that can play out with food is that normally you might say, “Hey, well, you know this donut looks really tasty, but I know it’s not good for me, so I’m not going to, I’m not going to eat it.” But if you haven’t slept enough, you might think a lot about how good it tastes and not very much about what it might do to your waistline later and so you’ll just eat it. There are multiple ways in which sleep restriction nudges some of your brain circuits in a direction that favors a higher intake of food and higher body fat in this.
Chris: Yet another reason to emphasize getting enough sleep on a regular basis. The more we learn about sleep, the more we see that it affects nearly every aspect of physiology by the circadian rhythm and other mechanisms. It’s just really hard to understate how important good sleep is.
4) Control your food environment
Chris: Before we finish up, I want to ask you one question that I think will be helpful for people as a takeaway. Given everything that we’ve talked about in your years of experience as a neuroscientist and your understanding of the brain and the role it plays in weight regulation, if there is one single piece of advice you’d give someone, a practical advice for preventing or reversing weight gain, what would that be?
Stephan: Yes. If I was limited to one thing, this is what it would be—the brain is highly reactive to the cues in your personal environment, and this is why the food industry spends over $10 billion dollars a year in the United States showing us images of food on TV and billboards and things like that. They do it because they make up that amount of money and more because they know that those food cues going into your eyeballs and into your brain make you buy and eat their food. Controlling the cues that you’re giving your brain and your personal environment is a very powerful way for you to either support or undermine your own eating goals.
What that means is that if you can design a food environment for yourself that doesn’t have calorie-dense tempting foods, especially not visible and especially not within arm’s reach, that’s really going to help you control your consumption of those foods and your overall calorie intake. The best thing really is to banish foods from your house that are not going to support your goal. That does two things. The first thing it does is it makes it just physically harder to eat those foods. But the second thing it does is that when those cues are not there, you’re not going to experience the same motivational drive. You’re not going to experience the same level of craving to even want those foods when the, when the cues are not there because that’s how your brain works. It looks for the cue, and then that’s a signal that something awesome is available, and then it triggers your motivation.
Chris: I’ve got, I’ve got a furry example of that. We have an eight-month-old Labrador retriever puppy right now. When we’re cooking dinner or there’s food out, she’ll just start to drool. The cues are coming into her brain and they stimulate this mechanism. She’s not thinking about it in the same way that we’re thinking about it but I’ve been just watching her. It really strikes me like this is something that’s so deep in our brain that we have to make these changes that you’re talking about to set us up for success because if we are trying to fight these hardwired mechanisms, it’s really really difficult.
Stephan: Yes, that’s a great point. I mean, really, the same is true in humans. It doesn’t just trigger your motivation, it triggers your physiology, your saliva flows, your stomach gastric juices start to secrete, you get more gastric motility, your small intestine starts to move around. Your body is ready to go whether that’s pizza or potato chips, anything that’s under your conscious control and often it’s something that you really don’t want yourself to do.
Chris: Right, right. I know I’ve mentioned this a couple of times, but I want to say it again because it can be pretty liberating for my patients when I explain this to them because I think a lot of people carry a lot of shame, feelings of guilt, unworthiness, and they feel like their tendency to overeat is some kind of character flaw rather than a hardwired biological survival mechanism that has nothing to do with their personality or who they are, their self-worth or their value as a, as a person and everything to do with just how our bodies and brains were programmed to survive in our natural environment and how that is just a profound mismatch with our current environment. When you think, when you frame it that way, it depersonalizes it, and when you remove that guilt and shame, it actually frees people up to take more effective action. At least that’s what I’ve seen when that lightbulb comes on and people don’t have to be stuck in that cycle of guilt-blame-shame-reaction, guilt-blame-shame-reaction, and they can just say, “Oh, this is an environmental problem, essentially. It’s a mismatch between my programming and my environment, so I need to change the environment.” And that’s essentially what you’re, what you’re saying with your number one piece of advice.
Stephan: Yes, absolutely. That’s a really interesting observation.
Chris: Stephan, thank you so much for coming on. Stephan’s book is called The Hungry Brain: Outsmarting the Instincts That Make Us Overeat, available at Amazon, at bookstores, all the typical places. I know you did a local event in Washington. Are you traveling around and doing any events or just sticking close to home?
Stephan: I don’t have any plans currently to travel around but we’ll see what happens.
Chris: Cool. Well, good luck with the book. I highly recommend it. I’ve been waiting for this book for a number of years because people always ask me what book would you recommend for a really evidence-based look at how we gain weight and the best way to keep it off. Until now, I haven’t really had one that I could point patients to or other clinicians to in my training program, and I’m really excited that this book is out there. You did a fantastic job. It was really fun to read as well. This could be a pretty dry topic, but I feel like your writing style, just as it always has been with your blog, is really accessible, and you have a knack for distilling complex concepts and making them easy to understand. I love some of the stories and the interviews you did with other scientists. I think that really helped bring it to life. Thanks for this book, and I wish you the best of luck with it.
Stephan: Thanks, Chris. I really appreciate that.
Chris: My pleasure. Take care, Stephan.
Stephan: You too.
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