Control Sugar Cravings & Metabolism with Science-Based Tools | Huberman Lab Essentials

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Welcome to Huberman Lab Essentials, where we revisit past episodes for the most potent and actionable science-based tools for mental health, physical health, and performance. I’m Andrew Huberman, and I’m a professor of neurobiology and ophthalmology at Stanford School of Medicine. Today, we are going to discuss sugar, in particular how our nervous system regulates our sugar intake and our seeking of sugar. We are going to place sugar into its proper context. The way I want to start off by doing that is to tell you a little bit of what happens when we eat and a little bit of what the brain does to respond to those events.

So, what happens when we eat? Let’s just take a what I call top-contour view of the hormonal response to ingesting food. Anytime we eat, that is the consequence of a number of things that happened before we ate. There’s a hormone in our brain and body called ghrelin, spelled g h r e l i n. Ghrelin is a hormone that increases depending on how long it’s been since we ate last.

Okay? So, the longer it’s been since we had a meal, ghrelin levels are going to be higher and higher and higher, and it essentially makes us hungry by interacting with particular neurons in an area of the brain called the arcuate nucleus of the hypothalamus and some other areas as well, like the lateral hypothalamus. And then when we eat, typically what happens is ghrelin levels go down. So, it’s a very logical system. Now, when we eat, assuming that we eat carbohydrates, but even if we just eat some protein and some fats, we will experience a slight or in some cases a large rise in blood glucose.

Blood glucose is simply blood sugar, and the body and brain, we should say, particular the nervous system doesn’t function well if blood sugar is too high or too low. So, as a consequence, we have another hormone which is released from the pancreas, which is called insulin, which helps regulate the amount of glucose in the bloodstream. Now, one of the chief organs for glucose utilization is the brain. Neurons are tremendously metabolically active, and their preferred mode of metabolism is glucose metabolism. The same thing is also true for the neurons in your body.

The way that you are able to move the limbs of your body, the way that you are able to perform exercise or movement of any kind for that matter, is because neurons called motor neurons send electrical potentials to the muscle fibers. Those neurons are also very metabolically demanding, especially when you’re doing demanding types of physical work, but also deliberate thought, deliberately controlling the way that your brain and body is moving requires more glucose uptake, more energy in those very neurons. And this is also why after doing a long bout of exercise, you might be tired, but also if you do a bout of skill learning of any kind, or if you’ve been reading and thinking about what you’re reading, or if you had a intense conversation with somebody where you’re really forcing yourself to listen, that’s work, and that work requires glucose uptake by neurons both in the brain and in your body. Now that we’ve established that glucose is the preferred source of fuel for the nervous system, I’d like to concentrate on a few of the other types of sugars that we ingest on a common basis and the impact that those have on brain function and body function. I’d particularly like to focus on fructose.

Fructose, of course, is found in fruit. It’s also found in the infamous high fructose corn syrup, which we will talk about today. It’s worth pointing out that the concentrations of fructose in fruit is quite low compared to the concentrations of fructose in high fructose corn syrup. Typically, the amount of fructose, fructose, I I think is the proper pronunciation that people are always correcting me, fructose, is anywhere from 1% to about 10%. Now, high fructose corn syrup is a different issue, and too much consumption of anything, but fructose included, can be a problem for the ways that it impacts the neural circuits that process sugar, not just glucose, but fructose.

One of the key distinctions between glucose and fructose is that fructose most likely cannot directly access the brain. It actually needs to be converted into glucose in the liver. And the way that conversion occurs feeds back to a set of hormones and neural pathways that we talked about earlier, which have a lot to do with appetite. And to just summarize what is now a a lot of very solid data, fructose, and specifically fructose, has the ability to reduce certain hormones and peptides in our body whose main job is to suppress ghrelin. So, although I, and I think pretty much everyone out there, save for a few individuals, agrees that calories in, calories out is the fundamental principle of weight loss, weight weight maintenance, or weight gain, ingesting fructose shifts our hormone system, and as a consequence, our neural pathways within our brain, the hypothalamus, to be hungrier, regardless of how many calories we’ve eaten.

So, current recommendations for most people are to eat more fruits and vegetables, but for those of you that are trying to control your hunger, ingesting a lot of fructose is probably not going to be a good idea. Certainly, ingesting it from high fructose corn syrup is not going to be a good idea because of the enormous percentages of fructose in high fructose corn syrup, 50% or sometimes even more. Fructose provides a bridge for us between a particular kind of sugar, hormone function, in this case, ghrelin, and the hypothalamus, which leads us to the next question, which is what is it about sugar that makes it such an attractive thing for us? Why do we like it so much? And the obvious answer that most people arrive at is, well, it just tastes really, really good.

But, that’s actually not the way it works. The rewarding properties, as we say, of sugar, whether or not they come in the form of sucrose or fructose, or foods that increase glucose to a a very high level, actually is not just related to the taste of the foods that produce that elevation in glucose, sucrose, or fructose. It is in part, but that’s only part of the story. And the rest of the story, once you understand it, can actually place you in a position to much better control your sugar intake of all kinds, but also your food intake in ways that can allow you to make much better choices about the foods you ingest. So, now I want to take us on a journey into the nervous system to explain the pathways in the brain and body that regulate our appetite for sugar.

Now, keep in mind what I already told you before, which is that when we ingest foods, they’re broken down into various components, and glucose is going to be shuttled to the brain, and of course to other neurons in our spinal cord and elsewhere, and to our muscles, et cetera, in order for all of those cells and organs and tissues to be able to function. The fact that so many cells and organs and tissues require glucose in order to function has led to a situation where you have dedicated neural machinery, pieces of your brain, that are almost entirely, if not entirely, devoted to seeking out of sugar or foods that contain sugars, and to make sure that you not only seek those out, but you know where those foods are, and that you ingest more and more and more of them. And there are two main ways that these neural circuits work. In fact, we can say that there are two neural circuits entirely that work in parallel. In the case of sugar consumption, the two parallel pathways involve one pathway related to the actual taste and the perception of sweet taste that lead not just you, but every animal that we’re aware of, to seek more sweet containing foods.

The other parallel pathway is related to the nutritive component of sweet foods, meaning the degree to