Huberman Lab | Episode – 64

Controlling Sugar Cravings and Metabolism with Science-Based Tools

Rating: 8/10

Listen on: Youtube | Spotify | Web


Sugar controls craving for foods that contain it in two ways. The rise in blood sugar in the gut and stomach as well as the sweet taste. Both are heavily used by the food industry, since both make us consume more, stop eating later, feeling full later, and develop preferences towards the food that has more sugar "hidden" in it.

Detailed Notes

Two mechanisms of how sugar changes us

  1. via sweet taste, we want to eat more of it, and others.
  2. via nutritive content, not only because of sweetness.

You can ingest too little sugar! Neurons can function less well because of too little sugar.

Main Goals of Episode: Answering the question of:

How much sugar should you be eating?

Sugar is Energy and Fuel source #1 for the brain.

Refined sugars are bad - especially those high in fructose content.

Calories In / Calories Out Principle -> the only way to maintain weight

Sugar makes us eat more hence disrupting that balance of calories in/out.

Sugar prevents goals if consumed wrongly.

What happens when we eat? Ghrelin - increases over time since we ate last. Makes us hungry by interacting with Arceus Nucleus of the Hypothalamus and the lateral Hypothalamus. When eating, Ghrelin goes down.

Eating increases blood glucose. Too high and too low blood sugar are bad for the brain. Insulin keeps blood sugar within a "tolerance" range. Too high Blood sugar is toxic to cells. Insulin clamps blood sugar by putting it into cells of muscles and liver.

Neurons run on sugar.

In fasted states, this is not entirely true.

Neurons in the visual cortex are aligned with certain stimuli. Detecting them, responding to different kinds of lines, vertical, horizontal, 45 degrees etc. That's named orientation tuning. Visual representation is built up out of those orientation tuned neurons.

Sharpness of tuning is dependant on blood sugar! In fasted states neurons are less tuned than in fed states. Outside perception is worse.

During fasted states, neurons use fat derived nutrients instead of sugar.

Glucose is still the preferred fuel for the brain.

Your brain as an organ is a glucose consuming machine.

Astrocytes bring glucose to neurons. Especially transporting it across the blood brain barrier. They also play a role in shaping the brain via neuroplasticity.

Intense neural activity (thinking, reading, conversation, deliberate practice) feels tiring because of the glucose uptake of the brain areas involved. Eventually glucose is depleted, hence you become tired. Sluggish. Slow.

Fructose in fruit is lower in quantity than in high fructose corn syrup. Sucrose is usually low in fruits. 1-10 % depending on fruits. Fructose is handled differently from Glucose.

Glycemic Index of something - how fast blood sugar spikes after eating it.

Fructose can not go to the brain directly. It has to be converted in the liver. This conversion trips into hormonal pathways that control appetite. Fructose suppresses hormones and peptides that suppress Ghrelin. Therefore eating fructose makes us hungrier/less satiated. Regardless of how many calories eaten. Fruits and high fructose corn syrup can stimulate appetite.

Rewarding properties of sugars are not just related to their sweet taste.

Mango peel can be eaten! Nice.

We have neural machinery to seek out sugary foods. Parallel pathways exist for doing all kinds of things. To ensure behavior is done properly, usually more than one pathway exists to make things work.

For sugars it's one pathway for the perception of sweetness, the other pathway is related to the nutrition content, i.e. how much it increases blood glucose. Distinctly different pathways for other tastes and seeking out those foods. Sweetness pathways are hardwired in that way into all mammals, they even exist in fruit flies.

Taste + nutritive components make us eat more of something. Craving is for both taste and higher blood sugar.

Conscious perception - sugary taste is preferred.

Taste perception is not only on the tongue but also on the pallet as well as in the rest of the mouth. We have distinct sweet perceptors that react to certain molecules (like glucose and sucrose) - how do they work?

Perception of foods changes when we ingest sugar and things seem more appetizing to the brain, while tasting sweetness. Tasting sweetness makes you seek more sweet stuff and food in general.

Taking care of "sugar appetite" shifts the perception of food to come.

Dopamine of course plays a role in that. Mesolimbic reward pathway plays a role also. Of course Motivational pathways are used to motivate eating behavior. Striatum (Dorsal - upper and ventral - lower) play a role in those.

Sugar - specifically its sweet taste - activates dopamine in the mesolimbic pathway. Especially in sweet liquids. Even diet drinks without sugar but still with sweetness. The sweetness works as a motivation for further craving. Not as a satiety factor.

Book Recommendation: Dopamination - Anna Lembke

Again, Pleasure Pain Balance is mentioned. Increase in dopamine goes along with increase in perception of lack - missing something, feeling bad.

Sweetness provides quenching of craving, right as it pauses, brain and body want more. That's the pain pleasure balance at work. Getting dopamine back up is usually done by eating more of a sweet thing, but diabolically the same stimulus doesn't get dopamine back to the same level as before. That's how binging down a whole chocolate works.

This is so much like Buddhist doctrine... Every pleasurable thing contains within it the capacity for suffering. That's mapping 1 to 1 onto how dopamine works.

Lack of dopamine => craving. Pain. Motivation.

Dopamine pathways are not evil. Understanding them helps doing what you want instead of what evolution wants. Ingesting something sweet cascades into wanting more of that sweet thing (and other foods).

Post ingestive reinforcing properties of sugar. Below conscious detection. Independent of taste! They are subconscious, that's why the food industry adds sugar to everything if they somehow can.

Knockout mice without sweetness perception don't want sweet tasting things, but after around 15 minutes, the mice still learn a preference for the sweet liquid, even though they can't distinguish it by taste. But it's subconscious.

Neuropod cells, see also, Wikipedia.

Neuropod cells are neurons in the gut that respond to presence of sugar in the gut. They send signals because of sugars via the vagus nerve, which plays a role in relaxation among other things, nodose ganglion and then from there to the nucleus of the solitary tract. And of course also to the mesolimbic pathway.

TLDR: Gut neurons control motivation to eat more sweet foods subconsciously.

Both of these pathways together increase dopamine spikes in response to sweet things and thereby trigger motivation.

Hidden sugars trigger neuropod cells, intense cravings are designed by the food industry.

Not eating the thing that we crave is extremely hard because of the dopamine parallel pathways.

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