Essentials: Control Sugar Cravings & Metabolism with Science-Based Tools

Andrew Huberman, who introduces himself as a professor of neurobiology and ophthalmology at Stanford School of Medicine, frames this Huberman Lab Essentials episode around one question: how the nervous system regulates both how much sugar we take in and how much we seek it out. He says his aim is to put sugar "into its proper context". To do that, he first gives what he calls a "top contour view" of the hormonal response to eating, and points out that every meal is the result of things that happened before it.

The first of those things is ghrelin. Huberman describes it as a hormone that rises the longer it has been since we last ate. It makes us hungry by acting on neurons in the arcuate nucleus of the hypothalamus and in other areas such as the lateral hypothalamus. Eating typically brings ghrelin levels down again, which he calls "a very logical system." Eating also raises blood glucose, slightly or in some cases a lot. He notes that this happens mainly with carbohydrates but can also follow a meal of only protein and fats. He stresses that the nervous system in particular "doesn't function well if blood sugar is too high or too low."

That sensitivity is why insulin matters. Insulin is released from the pancreas and helps regulate the amount of glucose in the bloodstream. Huberman then names the brain as one of the chief organs that uses glucose. Neurons are "tremendously metabolically active," he says, and glucose is their preferred fuel.

Huberman extends the point from the brain to neurons throughout the body. Motor neurons let us move our limbs by sending electrical potentials to muscle fibers, and he says these neurons are very metabolically demanding, especially during hard physical work. He applies the same reasoning to mental effort: deliberately controlling how the brain and body move "requires more glucose uptake, more energy in those very neurons."

He offers this as an explanation for ordinary fatigue. People may feel tired after a long bout of exercise, but also after skill learning, reading while thinking about the text, or an intense conversation in which they force themselves to listen. In his words, "that's work, and that work requires glucose uptake by neurons both in the brain and in your body." He cites no specific study here. The argument rests on the general principle he has just set out.

After establishing glucose as the nervous system's preferred fuel, Huberman turns to other common sugars, mainly fructose. It is found in fruit and in what he calls "the infamous high fructose corn syrup." He draws a quantitative contrast. In fruit, he says, fructose makes up "anywhere from 1% to about 10%." In high fructose corn syrup the share is "50% or sometimes even more." He adds a broad caveat: too much of anything, fructose included, can be a problem because of how it affects the neural circuits that process sugar.

The key difference he draws between glucose and fructose is about access to the brain. He hedges this claim: fructose "most likely cannot directly access the brain" and has to be converted into glucose in the liver. That conversion, he says, feeds back onto hormones and neural pathways closely tied to appetite. He describes the evidence as "what is now a lot of very solid data," but names no particular studies in this part of the episode.

fructose, and specifically fructose, has the ability to reduce certain hormones and peptides in our body whose main job is to suppress ghrelin.