Overeating and The Hungry Brain with Stephan Guyenet | EP#73
Stephan Guyenet, Ph.D., explains how our appetites and food choices are led astray by ancient, instinctive brain circuits that play by the rules of a survival game that no longer exists. And these circuits don’t care about how you look in a tri suit next summer.
In this Episode you'll learn about:
- The Food Reward system
- The brains valuation of food and Optimal Foraging Theory
- Delay Discounting and the Stanford Marshmallow experiment
- How the lipostat works against your attempts to reduce body fat
- Satiety, and the factors that can increase (and decrease) our satiety per calorie
About Stephan Guyenet’s book The Hungry Brain
- The book bridges the gap between the scientific research on obesity, eating behaviour, and what the public knows about them.
- It focuses on the fact that the brain generates all behaviours, feelings, and impulses. So it’s a key perspective to take when thinking about eating behaviour and obesity.
- I’m trying to understand the brain circuits that drive us to overeat even though we don’t want to overeat consciously or rationally.
Why non-conscious thinking makes us overeat
- The human brain is organized according to a couple of different overlapping or related principles.
- You have the least conscious and most automatic functions closest to the spinal cord. These are the things that regulate digestion, breathing, heart rate, etc.
- These circuits are really hard-wired and don't have a lot of flexibility. If they lose function, there are no other circuits that can take over for them.
- As you progressively move to evolutionary, more recent parts of the brain as you get further away from the spinal cord and closer to the cerebral cortex, you progressively get to functions that are progressively more conscious, flexible, and less hard-wired.
- These are the circuits that regulate emotions, stress, and stability or homeostasis over a bunch of different functions such as temperature and body fatness.
- Eventually, you get to the circuits that are the most flexible, the least hardwired, and the most influenced by what happens to you over the course of your life. That’s the things in the cerebral cortex.
- The cerebral cortex is an incredibly homogenous tissue. Its structure is very much the same over most of its volume but it performs all of these different functions as a function of its software rather than its hardware. If one thing gets damaged, the other parts can compensate. So it’s not a hard-wired tissue.
- That is the general overview of the hierarchy of the brain and how tasks are divided. But obviously, there are different levels of that organization that can be relevant to the same behaviours.
- For example, if you’re trying to make a decision about what to eat, you might have parts of your brain that are very ancient and impulsive that say, “Wow, I recognize that food has got lots of sugar and fat. So I’m going to trigger your intrinsic motivation - you’re craving, or maybe I’ll trigger your energy-seeking pathways – you’re hunger.”
- But then you might have these higher level, more flexible circuits that say, “Whoa! Wait a minute. Eating this food is not consistent with my higher level goals of physical performance in my triathlon, or maintaining my shapely figure for being in a bathing suit this summer, or not wanting to get diabetes.”
- So, you can’t really draw a completely clean line between the so-called “System 1” and “System 2”. System 1 being those more hard-wired functions. System 2 is the most flexible ones. However, I think it’s a useful division to take.
- Basically, you have this opposition that often happen between these two circuits. What drives overeating and obesity is the fact that you have these impulsive, non-conscious or minimally conscious circuits that are receiving cues from our crazy, modern food environment that are telling you to eat more food.
- This may not be consistent with your conscious goals about what you want to do. Nevertheless, it is a very powerful force. It’s not something that is very easy to fight on a continuing basis.
- This is true to anyone who has tried to lose weight whether it’s for sports, health, or physical appearance.
- This is the fundamental struggle that is happening in the modern world between these two different types of brain systems. The evidence suggests that the so-called System 1 or the more impulsive, less conscious circuits tend to be winning that struggle.
- Two different (but overlapping) brain circuit systems drive behaviour and eating. An ancient, hard-wired system for non-conscious thinking, and a modern, not so hard-wired system for conscious thinking.
- When it comes to non-desired eating eating behaviour, it is often a result of the former system being placed in an environment (a modern food environment) it was not designed for.
The Food Reward system
Natural selection is the highest level, most general lens that I apply to some of these systems because it makes a lot of sense.
- If we apply natural selection into foraging behaviour of our ancestors, what we see is that to have a successful organism that can have a high level of reproductive success, which is the currency of natural selection, you need to have an animal that can efficiently acquire energy from its surroundings.
- Energy is a concept that refers to potential energy stored in chemical bonds. To seek that energy effectively, you have to go after certain substances that contain those specific types of chemical bonds. These are carbohydrate, fat, and protein primarily.
- In natural selection, you’re trying to design an organism to be really good at passing on its genes in a natural environment. You’re going to design an organism that is motivated by specific chemical properties in food that are markers of its energy content. Again, these markers are carbohydrate, fat, and protein.
- That is exactly how we’re wired, not just humans but many other animals.
- We have specific receptors in our digestive tract that recognize carbohydrate, fat, and protein. Essentially, these things communicate to the brain and they cause certain parts of the brain to release dopamine that’s a really key event in our motivation and our learning to be motivated.
- The dopamine release is proportional to the concentration of those nutrients in the food. So when a food is very concentrated in these nutrients, you get a lot of dopamine release. This causes you to be motivated on a very basic, intuitive level which we call a craving to eat that food.
- Furthermore, it causes you to learn all the sensory cues that are associated with those nutrients. For example, if you eat ice cream, all that dopamine gets released. This causes your brain to remember the appearance and flavour of the ice cream, where you ate it, who you were with, the texture, and all of the sensory cues that predict the availability of that big delivery of nutrients.
- These become motivational cues themselves. So the next time you see the box of ice cream or the next time you smell it or have a little taste, it gets your dopamine spiking again and it pushes you to consume that food.
- This is very analogous to how things work in drug abuse. The reason drugs are addictive is that they cause dopamine release.
- This is how food reward works. If you look at the properties of ancestral diets, the diets of our distant ancestors, they tended to be less rewarding. They were unrefined which means that they were higher in fibre and water compared to modern foods.
- In our modern diets, we purify fats, sugar, glutamate, and salt to a pure state and add it to food. We’re distilling out these reward factors – the active ingredients that spike dopamine – and mixing them together in ways that are way more stimulating than what our ancestors had.
- So, it’s very difficult at this point to say no to these motivational triggers that are pushing us to eat those very seductive foods. In some people, this can lead to addictive-like behaviour by eating too much.
- When you eat certain substances, a dopamine release causes your brain to learn to get motivated by the food containing that substance.
- The level of motivation, or the reward, is proportional to the concentration of reward factors in the food.
- Some of the greatest reward factors are concentrated fats, sugar, glutamate, and salt.
- Since these are added to foods in a modern environment, our diets today are much more rewarding than our ancestors diets, which didn't contain these substances in high concentrations.
Is there a difference between sugar or fat in terms of which is the biggest food reward factor?
- There’s a lot of uncertainty that remains. What I can say that they are both very powerful reward factors.
- If you look at the foods that people report as being most commonly associated with cravings and addiction-like behaviour, generally, they are either combinations of sugar and fat, or fat and starch, or fat, protein and salt.
- Things that are just high in sugar and not in anything else are not associated with as frequent cravings or addiction-like behaviour.
- You can cut refined sugar out of your diet and most people will probably benefit from that in part because you’re cutting out a lot of calorie-dense, highly fattening foods.
- You can just as easily turn around and say, “Well, I’m going to cut all added fat out of my diet.” People would find if they do this that this would have very similar effects.
- If they cut out added fat and everything that contains it, they would find that it’s very difficult to do so because they’re accustomed to it. They want it and they like it just like sugar.
- Also, it tends to associate with a lot of calorie-dense processed foods. Cutting it out tends to reduce your calorie intake and your overall drive to eat.
What is the optimal foraging theory (OFT)?
- This is a discipline developed by biologists approximately 50 years ago to model the foraging behaviour of wild animals.
- They’re basically trying to understand the principles that determine food selection and consumption in wild animals.
- What they came up with is the finding that energy or calories or joules is the most important factor in food selection for most omnivorous species that could choose between many different foods.
- If you just model food selection behaviour simply based on the calorie value of everything in the environment, you’ll get a pretty decent picture of what an animal will select in real life.
- This is extraordinary, but not obvious because an animal like humans needs many different nutrients to be healthy. It’s not just about calories. Yet, apparently, natural selection pays very close attention to calories.
This is the key limiting factor in the survival and reproduction of wild species.
- You can boil this down to a very simple equation. That equation is the value of a food item equals the number of calories in that food item minus the number of calories it takes you to obtain and process it divided by time. So it’s just the calorie return rate.
Food Value = (Food calories - calories expended) / Time
- This predicts foraging behaviour. It turns out to work well even in “wild humans”. In other words hunter-gatherers.
- The human brain really appears to be hard-wired. Not just humans but many species appear to be hard-wired to intuitively apply this economic equation to their food selection behaviour.
- One thing that you might predict from this is that if the value of food is very high, in other words, if it contains a lot of calories, it requires very little time and effort to obtain, process, and consume, then you would expect hunter-gatherers to take advantage of that situation and eat a lot of it.
- Anthropologists I interviewed described hunter-gatherers chugging up to a litre of honey, eating 30 wild oranges that are the same size and sweetness as supermarket oranges, and eating 5 pounds of fatty meat.
- Essentially, they become completely gluttonous when they have the opportunity to do so. But it’s good for them.
- This is a key thing to understand. That our ancestor's gluttony was a good thing. There was no social stigma about overeating. The more that you could eat, the better.
- The reason is that hunter-gatherers have fluctuating energy ability in their environment. They don’t always get to eat as many calories as they want and as many calories from the foods that they want.
- So when those things are available, they take advantage of it and that helps their survival and reproductive success by helping them build strong bodies, by helping pregnant women come to term, and by being able to feed infants properly and give them enough calories and nutrition.
- Basically, these are the same things that are wired into our brains today non-consciously. We don’t actively think about this. We’re not doing these calculations. Animals are not doing these calculations consciously but they are being made at some level in the brain which is affecting our food intake behaviour.
- So when we’re in a situation where food is very easy to get, very convenient, and very calorie dense, we have this instinctive, impulsive drive to take advantage of it for many of us, which of course varies from person to person.
- A great example of this is free food. In the US, a lot of people bring food to work like brownies, pizza, or doughnuts. They bring it into meetings. So you have this very calorie dense food that’s essentially right in front of you and costs you nothing in terms of money or effort. It can be very hard to say no to that and not overeat even though you don’t want to eat it, and you know it’s unhealthy and inconsistent with the conscious goals for yourself.
- We make unconscious food value calculations that govern eating behaviour.
- If a food has lots of calories, is convenient to get quickly and inexpensively, then it has a high value to us and we are driven to consume it.
- In our modern food environment, these kinds of foods are all around us.
Delay Discounting and the Stanford Marshmallow experiment
- In the Stanford Marshmallow Experiment, they put kids in a room by themselves with a marshmallow. They told the children that if they can go for 15 minutes without eating the marshmallow, they will get another marshmallow.
- Then they measured whether the child would wait or eat the marshmallow. If they did eat the marshmallow, they measured how much time it took before they ate the marshmallow.
- Almost all the children ate the marshmallow, very few of them waited for the second marshmallow, which is consistent with kids being very impulsive.
- What they found was that the longer the children waited, the leaner they tended to be as adults.
- Basically, the more they valued a future reward in relation to an immediate reward, the less their weight crept up over time.
- This really gets into a concept called Delay Discounting. This is the idea that we discount or devalue things that are going to happen in the future to us relative to things that are happening right now.
- This is a really important concept. Because we often make decisions where some of the consequences of that decision are right now and some of them are later.
- A simple example is that when you eat a cookie right now, the immediate benefit is the pleasure and reward value of it. You enjoy eating that cookie but there’s a delayed cost. The delayed cost is that the cookie may take you one step closer to obesity, diabetes, cardiovascular disease, not fitting into your swimsuit next summer, or not winning your triathlon, etc.
- You’re essentially making a decision between your current self and your future self, which one you value more. Most people value their current self more than their future self.
- This leads to disastrous consequences. Eating behaviour is just one of them but obviously, there are major financial consequences as well with people who are overspending or gambling.
- These are people who are making a very destructive trade-off between their current well-being and their future well-being. They’re essentially short-changing their future selves.
- What we see is that people who have less delay discounting or those who value their future self almost as much as their current self, tend to do better in a variety of life outcomes. Body fat control is one of those things that they do better in.
- It actually makes sense to value your future self less. The reason is that the future is uncertain whereas the present is certain. In a hunter-gatherer setting where our ancestors lived, or even in recent non-industrial agricultural settings, the future is very uncertain. You have a 50% chance of being dead by the time you are 35. There are accidents, warfare, infectious disease, no legal accountability that we have in modern society.
- So, it makes sense to have this intuitive impulse to greatly discount the future and we’ve inherited this from our ancestors.
- Today it’s different. We have very low mortality rates. We can put money away in a retirement account that we won’t touch for 30 years and we can trust that it will be there as long as the economy doesn’t collapse. So, there’s incredible stability in the modern world that we never had before.
- This means that it makes a lot more sense to value our future selves a lot more than we used to.
- Delay Discounting means that we discount or devalue things that are going to happen in the future to us relative to things that are happening right now.
- In other words, the immediate benefit and reward for our current self of eating certain foods tends to win over the potential costs (health, performance, looks) of eating this same food item for our future self.
What are the lipostat and satiety? How do these affect our eating behaviours?
- There are systems that control the energy status of the body. These are both situated in the brain.
- There’s a short-term system that is in the brain stem that I call the satiety system. This regulates your energy status on a meal-to-meal basis.
- What happens as you eat a meal is that signals go up from your digestive tract to your brain getting information about what you ate. Like the volume of what you ate from stretch receptors in your stomach, chemical composition from receptors in your small intestine and mouth, etc.
- All this information gets integrated into your brain stem which makes all these complex computations. But the only thing you’re aware of is whether or not you feel full. This is the conscious output of the system.
- This ties into other systems that cause you to terminate your meal once you reach that state. Your motivational systems get turned off. Your motor systems stop driving your hand with the fork going down to the plate.
What are the factors that affect how satiating a type of food is in this meal-to-meal system?
- How satiating a food is, is only loosely related to the number of calories it contains. So you can kind of trick your satiety system into feeling fuller with your calories if your food has specific properties.
- That includes food that has a lower calorie density - fewer calories per weight or volume. That would be like oatmeal versus crackers. Oatmeal has a lot more water and fibre. So the same number of calories will fill you up more.
- Food that is less palatable. The more delicious a food is, the less it fills you up per unit calorie.
- Higher fibre and protein fill you up more per unit calorie.
- Essentially, any kind of food that we intuitively recognize as fattening like ice cream, candy bars, pizza, or chips, invariably have physical and chemical properties that lead to less satiety per calorie.
- They typically have low fibre, high-calorie density, high palatability, and sometimes low protein but not always.
- This means that it requires you to eat more calories before you reach that point of satiety that causes you to terminate your meal.
- Conversely, foods that are more ancestral, that we think of as more slimming like whole, unrefined foods – potatoes, vegetables, fruits, meats, eggs, etc. - are on the opposite side of the spectrum where they have properties that provide greater satiety per calorie.
- The other system is the energy homeostasis system or lipostat. The lipostat governs body fat stability.
- What this system does is it regulates your body fatness, which is your long-term energy status.
- This long-term regulation is happening in the hypothalamus.
- The way this works is that body fat produces a hormone called leptin, in proportion to its (the body fat store's) size. The brain measures the level of leptin in your circulation using receptors. It then uses this information to enact corrective responses to bring your body fat back up if you start to lose fat.
- These responses include activating your hunger and food motivation systems so you’re going to crave more. You’re going to be hungrier. You’re going to respond more to visual and smell cues of food. You’re going to think more of food.
- On the other side, it starts to lower your metabolic rate and make you perhaps feel colder and less interested in physical activities.
- So it’s trying to bring more energy into your body and allow less energy to leave your body in order to restore your lost fat.
- This is one of two key reasons why fat loss is so difficult. The other one just being that we have our habits and we don’t like to stick to weight loss diets.
- The long-term system, the lipostat, sets the gain of the short-term system. It tells the short-term system how much food it should require for achieving that state of fullness.
- Let’s say you’ve lost weight. Your leptin has gone down. Your lipostat has activated a starvation response. Through its communications with the brain stem, it’s going to say that you need to eat 50% more food at each meal to achieve the comfortable feeling of satiety. If you don’t, you’re still going to be hungry. This is part of the way that the brain tries to restore lost body fat.
- This is a very important system to understand for anyone who’s trying to modify their body fat. Understand that you’re actually fighting this regulatory system.
- However, that lipostat set point (the body fat level it defends) is not rigid. It depends to some extent on the circumstances of your life and of your diet.
- We don’t have a lot of definitive information about how you can modify the set point around which the lipostat regulates your body fatness but we have some suggestive clues.
- One of them is that if you tend to eat a lower palatability, reward, and calorie density diet, that tends to make the lipostat defend a lower level of body fatness. It’s very easy to demonstrate in rodents that they will defend different levels of body fatness against changes depending on the dietary context you placed them in.
- Also, higher physical activity seems to lower the set point, at least in some people. Better sleep and stress management are also among the things that there’s at least strong indirect evidence that the set point can be modified.
What are some practical applications that we can do to prevent ourselves from overeating?
- I tend to look at things from the non-conscious brain circuits. The path to sustainably manage your eating behaviour is to give them the right cues, because these systems are very responsive to the cues that they’re receiving from inside and outside your body.
- You can’t directly control the activity of these circuits but you can indirectly control them by giving them the right cues.
- There are two things that I really like to focus on. One is your food environment. You can have a diet that’s relatively healthy but if you’re surrounded by tempting foods all day, you’re going to tend to eat too much.
- Regulating the cues that you’re feeding those circuits will help to control the activity of those circuits. In your home or at work, you can do this by not having food on the counter, not having food visible to you, and not having things that you can just grab easily and eat.
- You can create small effort barriers like having nuts with shells, or fruits that you have to peel like oranges. Little things like these help align your eating behaviour with your true needs.
- So the food environment is very important and this is one of the main things that has made us fatter over the last few decades.
- The second thing is the satiety component. Eating foods that trigger more satiety per calorie at a particular meal give the non-conscious satiety circuits the right cues that help align your eating impulses with your eating goals.
- These are the foods that have lower calorie density, moderate palatability, higher protein content, and a higher fibre content.
Favourite book, blog, or resource:
- The book Salt Sugar Fat by Michael Moss
Favourite Hungry Brain approved food:
A personal habit that helped you achieve success:
Links, resources and contact
Links and resources mentioned
Connect with Stephan Guyenet
Connect with host Mikael Eriksson
Hi! I'm your host Mikael,
I am a full-time triathlon coach and an ambitious age-group triathlete. My goal is podium at the Finnish national championships within the next few years.
I first started the website Scientific Triathlon in autumn 2015 as a passion project to share my learnings with a larger triathlon audience. Later on, in early 2017 I started the podcast That Triathlon Show.
I sincerely want you to contact me to
- Send me feedback
- Give constructive criticism
- Request topics and guests for the podcast
- Send me your triathlon-related questions
- Tell me that you've rated and reviewed That Triathlon Show so I can give you a shout-out on the show and tell you how much it means to me!