So these ultra-processed foods have a number of features that make them, make people prone to gain weight. And there's really beautiful work, I don't know if you know this, from Kevin Hall at the NIH who's investigated this. He's really, in my opinion, the best person doing this kind of human obesity research today.

And he does these experiments where he takes people into the NIH, into the hospital, hospitalizes them for several weeks so he can exactly control what they eat. And he did this beautiful experiment where basically he had chefs prepare two kinds of food, one ultra-processed and the other not ultra-processed, sort of more whole foods, more healthier foods, but had them take a lot of care so that when they gave the foods to independent raters, to people to test, they would say, "This is about equally palatable." So I like this ultra-processed dish as much as this non-ultra-processed dish.

What's an example of an ultra-processed dish, like an out-of-package macaroni and cheese? Exactly, that kind of stuff. With bacon kind of thing? Exactly. Versus some pasta sitting next to a vegetable and a nice piece of... Salmon or something. Exactly, exactly. Okay. And took people into the hospital, basically allowed them to eat just as much as they would like first of the ultra-processed meals.

So they had the selection of ultra-processed meals for a couple of weeks, and then switched them to the non-ultra-processed meals, and then also did it in the reverse order. So the other half of the people, they got the regular food first, then they got the ultra-processed food. And what he found is that even though people rated the foods as equally palatable, they ate much more of the ultra-processed food.

And they actually gained weight during that two-week period when they were being given the ultra-processed foods. And then when you switched them, they lost weight. So the idea being that you can have two sets of food that you have equal preferences for, but something about the ultra-processed food is making you eat more of it when you actually consume it.

And there's a number of ideas about why that could be. So one idea is that these ultra-processed foods have been optimized to have the right percentage of fat and sugar and protein to sort of promote more consumption once you start eating it. So that could be part of it.

Another idea is that, you know, a big thing about whole foods is that they take more energy to digest and they have more volume. So one of the striking things from that study is if you just look at the pictures of the meals, they're the same number of calories, but there's so much more food, seemingly, on the non-processed food versus the ultra-processed food.

And that's just because whole foods are bigger, because they're not so energy dense. And we know that, for example, volume is a major signal in the short term for regulating food intake. So if you just eat more volume, that could be valuable. And there's lots of things like that.

So I think that's another plausible hypothesis, but the truth is we don't really know. - I have a hypothesis and I don't want to force you into speculation, but given that you've studied and discovered that the neurons and circuits involved in appetitive and consummatory behaviors can learn based on experience and expectation, I think it's fair game to at least ask your thoughts on this.

So I've been paying a lot of attention to the landscape of what the general public think about, let's call them elimination diets, where people will just eat meat, or will go onto a vegan diet, or do some time-restricted feeding, or do any number of different things that have been shown to promote weight loss, provided people obey the laws of thermodynamics and consume fewer calories than they burn.

I do believe in calories in, calories out, and there are a number of different routes to get there, and some are more painful, some are less painful, and it depends on the individual lifestyle exercise and on and on. But let's just suppose for a moment, based on Kevin's work on highly processed foods versus whole foods, that there's a learning that takes place when we eat, and that this learning takes place over time, such that our brain and appetite start to link the variables of taste, macronutrients, proteins, fats, and carbohydrates, so knowledge about macronutrients, a piece of fish is mostly protein, has some fat, a bowl of rice is mostly carbohydrate, has some protein, put a pat of butter on it, has some fat also, it's sort of obvious.

But taste, macronutrient content, calories, which we already know people with anorexia are exquisitely good at counting with their eyes. So it's possible they represent, again, a pathologic extreme of this. And micronutrient content, maybe even amino acid content, like how much leucine is there. Now, most people aren't thinking about how much leucine is in a meal, but we know that leucine is important for certain aspects of muscle metabolism.

It's present in certain proteins and not others. You're going to find less of it in a vegetable, typically, than you would in a piece of chicken and so on. And that when people eat mostly non-processed or minimally processed foods and not in combination, so we're not talking about stewing all this together or blending all of it together, which sounds disgusting, right?

Broccoli, rice, and a chicken breast blend together, it just sounds horrible, but eating them separately, if there's some olive oil and a little pat of butter involved, like that sounds pretty good. But a highly processed food in some ways is a blending together of macronutrients, micronutrients, if there are any, and other features of the food that neurons in the brain seem to pay attention to, and then giving it a unified taste, a Dorito, right?

A candy bar that we attach to the product, we attach to the name of the processed food, to the packaging. But I could imagine, and here's the hypothesis, that that is "confusing" to our neural circuits in a way that doesn't match up well with our thermodynamic requirements of how much we're burning versus how much we need to eat.

Whereas when I eat a piece of steak and a vegetable, I actually want less carbohydrate afterwards. If I eat the carbohydrate first, for me, it's difficult because I love the taste of carbohydrates, especially when they're combined with fat. But there seems to be an easier time regulating food intake when people step back and say, "I'm going to consume minimally processed whole foods." And I'm guessing it's not just because they're trying to be healthier, that might be what stimulates the shift, but that the brain starts to learn the relationship between food volume, smell, taste, what these things look like, and satiation at the level of, "Oh, that's enough amino acids because I had a piece of fish, so maybe I don't need to consume as much of some other things." Or the vegetables provide volume and fiber, and often vegetables can taste really delicious too.

So that there's a linking of nutrients, calories, and taste in a way that's more appropriately matched to the energetic demands of the organism, in this case, us humans, that highly processed foods bypass. Now, I realize that was long-winded and forgive me, but my audience is used to that. Whenever I'm trying to table something for, no pun intended, for discussion that I would like to think can at least stimulate some additional thinking about a landscape, in this case, nutrition and feeding behavior, that for a lot of people is just really confusing.

And here's why. And this is the last thing I'll say. I have several friends who have been very overweight their entire lives, for whom the following diet has worked exceptionally well. I'm not a diet coach. I'm not a nutritionist. I don't pretend to be one. I say eat proteins like meat, fish, eggs, vegetables, and fruit, and do that for a couple of months, and then add back in starches as you see fit based on your food intake.

And without fail, they all lose a ton of weight. They're very happy with that. They add back in a minimum of starches, they keep the weight off, and they're also exercising, but not more than they were before in most cases. And I don't think that it's meat or fish or vegetables per se.

I think it's that they finally develop an appreciation for what different foods have in terms of what they actually need. And without fail, they all say, "Oh, you know, I went to this party and I had a piece of cake and it didn't taste good to me after three or four bites." So that's interesting too.

So I just would like your thoughts on this. We're not defining any new diets. I don't sell any diets. I don't do any of that. But I find it amazing that when people start eating minimally processed whole foods, I have to assume that their brain changes as it relates to appetite, craving, and just kind of an unconscious understanding about what food is providing them or not.

And that highly processed foods basically bypass all of this and just get you to consume more, perhaps in hopes of getting something that you probably aren't getting at all or that you need to consume a lot of this food in order to get. There are several interesting ideas there.

So there's two that come to mind just thinking about what you just said. So the one is the idea of what's going on when these people consume simpler diets, more of whole foods. And one thing I think that's very likely going on is this phenomenon of sensory-specific satiety as being engaged.

And so sensory-specific satiety is just the idea that as you expose yourself repeatedly to a certain flavor or taste, you basically lose appetite for that. You get specific loss of appetite for that flavor or taste. This is why, as you said, basically if you start off eating the protein, after a while you're like, "I don't want any more salmon, but I would like some carbohydrates now," because you have this sensory-specific satiety.

And so it's well known, actually, that if you simplify your diet, make your diet really simple, so there's just a few things, the sensory-specific satiety alone can cause you to eat less, basically, because there's just less variety in your diet and you don't want to eat more of that same thing.

And so I think a lot of diets, actually, it's not about the specific macronutrient or the specific food, it's just that they're reducing the variety in the diet. Eventually you just get sick of eating the same thing. And the thought behind that idea is that it's important evolutionarily so that you eat a diverse diet.

It's the reason, probably, that you want sweets after you've eaten a savory meal and so on. A second idea, though, that comes to mind is just, as you mentioned, this idea of learning. And so much about our preferences for food, they're not innate, they're driven by learning. And so there are some things that are innate.

So if you put sugar on a baby's tongue, it'll smile, indicating that it likes it. And if you put something bitter, it'll frown. And a rat will do the same thing, a neonate rat. But most of flavor and the perception of food is not just sweet or bitter, it's this much more complex sensation that involves smells, it involves taste, and then it involves how those tastes and smells interact with the post-ingestive effects of the nutrients.

So the sensing of those nutrients in your stomach and in your intestine, primarily in your intestine, are thought to then feed back and then change your preference for these foods. And so there's lots of examples of this that you can just imagine from everyday experience. Most people, the first time they had a beer or the first time they had a glass of coffee, found it repulsive, right?

Because it's extremely bitter. But then we come to crave these things because we know what they do to our body, we like what they do to our body. And that doesn't just make us take them like they're medicine, we actually somehow change our very perception of how that flavor is.

We actually come to savor that flavor we previously found disgusting. And it's because our sensation of whether something's good or bad depends on our internal state. And so it's an interesting idea, perhaps if these ultra-processed foods that have so many different ingredients and such an unnatural combination, perhaps this process of learning about the nutrient content of different foods and flavors becomes impaired because it's just the brain is not used, the brain's used to saying, this is a piece of chicken and this is primarily protein.

And so I can gauge from this flavor, I can connect this flavor to an amino acid content, but something that's so diverse, it might be harder to do. - And isn't it the case that the neurons in the gut and the hormones that are produced by the gut as we digest food, and that the neurons in the brain that control appetite and feeding have to be tuned to macronutrient content, because those are the primary colors of nutrients and nutrients are the way in which we can persist on a day-to-day basis, right?

I mean, I'm not trying to sound more sophisticated where simpler terms would suffice. What I'm basically saying is that the neurons in our brains that control these behaviors, both eating and cessation of eating an ingredient or an entire meal, can't be tuned to a particular food product or to chicken or to an egg or to a steak or to lentils, but rather to amino acid content, essential amino acid content in particular, essential fatty acids.

And in the case of carbohydrate, whatever is going to replace whatever glycogen we might have depleted, right? I mean, like if we really break it down into biology, eating is for a purpose. And my understanding is that the purpose of eating is to replace those things as needed rather than to, you know, taste savory or taste, you know- Absolutely.

Absolutely. Absolutely. Those are just, those sensory cues are just markers that tell the brain what might be in that substance. Thank you for tuning in to the Huberman Lab Clips channel. If you enjoyed the clip that you just viewed, please check out the full-length episode by clicking here.