How Our Hormones Control Our Hunger, Eating & Satiety
This episode explores the complex interplay between hormones from the gut, liver, pancreas, and brain that regulate appetite, hunger, and the feeling of fullness. Dr. Huberman explains specific neurons and hormones like ghrelin, MSH, and CCK that control our desire to eat or stop eating, and provides practical tools including meal timing strategies, supplements, exercise protocols, and dietary approaches to optimize these systems.
1. Introduction to Neural Control of Hunger
The podcast dives into how hormones work together with the nervous system to control whether we want to eat more, less, or stop eating altogether. Dr. Huberman emphasizes that there are multiple "entry points" for tools you can use to regulate hunger, meal timing, and satiety.
The first key brain area to understand is the hypothalamus, located at the base of the forebrain. This region contains neurons controlling many functions including sexual behavior, body temperature, circadian rhythms, sleep, and even rage.
"There are actually neurons that if we were to stimulate them would send you or anyone into a rage. They're just powerful control centers for the brain and body."
Within the hypothalamus, there's a specific area called the ventromedial hypothalamus that researchers have studied for its relationship to hunger and feeding. Interestingly, this area creates paradoxical effects:
- Some lesions make animals or people hyperphagic (wanting to eat excessively)
- Other lesions make them anorexic (not wanting to eat at all)
This tells us the ventromedial hypothalamus is definitely important for hunger control, but there's something more complex going on beneath the surface.
2. The Role of Chewing and Touch in Eating
Beyond the hypothalamus, there's another neural component involving your mouth. The insular cortex, located higher up in the brain, processes information about what's going on inside you (called interoception).
This brain area receives input from touch receptors in your mouth and has powerful control over:
- Whether you're enjoying what you're eating
- Whether you want to avoid certain foods
- Whether you've had enough
- Whether you want more
"I'm one of these people, I love eating so much, that I just like the mere act of chewing."
Dr. Huberman shares that he personally finds the act of chewing pleasurable, which is why people enjoy chewing gum or crunching on celery sticks. The key insight here is that touch and texture play a huge role in our eating experience, not just taste.
The consistency of food matters tremendously – some people love the texture of urchin at sushi restaurants, while others find it off-putting. This preference is highly individual, probably learned, and potentially influenced by cultural background.
One important note: chewing something without calories (like celery or sugar-free gum) won't drive increased hunger. However, eating something with sugar has a very specific action that promotes the desire to eat more.
3. The Parabiosis Experiment: Proof That Hormones Control Hunger 🐀
A classic experiment demonstrated the crucial role of hormones in hunger control. Researchers took two rats and parabiosed them together, meaning they surgically linked their blood supplies so they could exchange factors in the blood while keeping their brains and mouths separate.
When they lesioned the ventromedial hypothalamus in one rat:
- That rat became extremely obese – a "super rat, jumbo rat"
- The connected rat became very thin and lost weight, despite eating the same amount as before
"This tells us that there's something in the blood that's being exchanged between the two animals... And that tells us that there's hormone or endocrine signals that are involved in the desire to eat, and hunger and appetite."
This groundbreaking experiment proved that hormonal signals are essential players in controlling our desire to eat.
4. The Arcuate Nucleus: The Brain's Appetite Control Center
One of the most exciting discoveries in feeding science over the last 20 years is the arcuate nucleus, a brain area containing fascinating neurons that release incredible molecules into the blood.
POMC Neurons and Alpha-MSH
The first set of neurons are called POMC neurons (Proopiomelanocortin). The "melano" in the name hints at its connection to pigmentation and melanin.
These neurons produce Alpha-MSH (Melanocyte-Stimulating Hormone), which Dr. Huberman emphasizes is crucial to remember:
"If you don't want to remember any of the other acronyms and terms I've talked about this episode so far, do try and remember M-S-H, okay? Mouse, Sam, Hamster, M-S-H, okay? MSH reduces appetite and it's a powerful molecule."
AgRP Neurons
The second population of neurons are called AgRP neurons, which stimulate eating. Whenever you're approaching food or feeling excitement (or even anxiety) about eating, these neurons are active.
Key findings about AgRP neurons:
- Activity goes way up when animals or people haven't eaten for a while
- If you kill these neurons, animals and people stop eating entirely
- If you stimulate them, animals or people will eat to the point of bursting
"Which just sounds horrible, but it just tells you this is the accelerator on eating."
5. Sunlight and MSH: Why Light Suppresses Hunger ☀️
Here's where things get really interesting. Alpha-MSH is activated by ultraviolet light to the eyes – not to the skin or directly to the pituitary, but through the eyes.
This is why:
- Getting ample sunlight helps keep appetite in healthy ranges
- In spring and summer months, animals and people generally eat less
- In cold winter months, appetite increases (and it's not just because of holiday foods)
"If you're getting ample sunlight to the eyes, it's converted into a signal for the MSH neurons... And then MSH can bind its receptors, and can keep the brake on appetite in check."
Practical Takeaway
Make sure you're getting enough light throughout the day – not just in the morning. This means:
- Avoid wearing sunglasses when it's safe to do so
- If you lack access to sunlight, use artificial light
- Avoid blue blockers during the daytime (they block the UV and shorter wavelength light needed for MSH release)
The Underground MSH Scene
Some people actually inject MSH or similar compounds, which Dr. Huberman does not recommend. The three main consequences are:
- Reduced appetite (used as a dieting drug)
- Becoming very tan
- Dramatically increased libido – to the point of priapism (chronic erection that can actually cause physical damage)
6. Ghrelin: The Hormone That Determines When You Get Hungry 🕐
Ghrelin (spelled G-H-R-E-L-I-N) is released from the GI tract and its main role is to increase your desire to eat. It works through several mechanisms:
- Stimulates brain areas that make you want to eat
- Creates food anticipatory signals in your nervous system
- Makes you start thinking about foods you like at particular times of day
"Ghrelin is sort of like a clock, a hormonal clock that makes you want to eat at particular times."
The signal for ghrelin release is reduced glucose levels in the blood. But here's the fascinating part: ghrelin also gets input from a clock in your liver that's linked to the clock in your hypothalamus.
This means if you eat at regular meal times, you'll start getting hungry a few minutes before those times. That stomach growling? That's ghrelin at work.
7. Meal Timing Determines Hunger, Not the Other Way Around
This is a crucial insight: when you eat controls your appetite, not the other way around.
Looking at the extremes:
- Some people feel they need to eat every 2-3 hours or their blood sugar drops
- Others eat once or twice a day during a limited feeding window and feel fine
For those who eat on a very regular schedule, their ghrelin secretion matches their eating times. This creates a predictable hunger pattern.
Dr. Huberman discusses his colleague at Stanford (now at Neuralink) who has a clever practice:
"He keeps his ghrelin system at random. What he does is he skips one meal per day and he makes his external schedule dictate that. So, sometimes he skips breakfast, sometimes he skips lunch, sometimes he skips dinner."
This approach keeps the ghrelin system "off kilter" and builds what's called top-down control – the knowledge that the hunger you're feeling isn't necessarily hypoglycemia, but rather just an activation of AgRP neurons.
8. The 45-Minute Rule for Shifting Meal Schedules
If you want to shift your feeding schedule, here's the practical guidance:
The neural circuits that link the ghrelin system to feeding control can handle shifts of about 45 minutes per day. This is a form of neuroplasticity.
Example Protocol
If you normally eat breakfast at 8:00 AM and want to start eating your first meal at noon:
- Take 4-5 days for the transition
- Push your meal out by about 45 minutes to an hour each day
- Continue until you reach your target eating time
"So it's not quite as painful. Or you can just take the plunge and just do it all at once."
Dr. Huberman shares his own experience transitioning from eating every 3-4 hours to eating twice a day (lunch and dinner):
"At first it was excruciating. I remember thinking like, this is really brutal pushing out feeding."
But now we know that for most forms of exercise, you can train fasted just fine, primarily relying on glycogen from the liver and body fat for longer exercise bouts.
9. CCK (Cholecystokinin): The "No More!" Hormone
CCK (Cholecystokinin) is released from the GI tract and is potent in reducing hunger levels. Its release is governed by:
- Specialized neurons that detect what's in the gut
- Elements of the mucosal lining and gut microbiome
"CCK is stimulated by fatty acids... amino acids... as well as by sugar."
What Triggers CCK Release?
Omega-3 fatty acids from algae, krill, or fish oil, plus Conjugated Linoleic Acid (CLA) from food or supplements, stimulate CCK release, which blunts appetite.
The other major trigger is amino acids, particularly glutamine, an essential amino acid.
10. We're All Fat and Amino Acid Foraging
Here's a profound insight about eating:
"Most people don't understand that when we're eating, we are basically fat foraging and amino acid foraging."
Studies show that people and animals will essentially eat until they feel they've consumed enough:
- Omega-3s
- Omega-6s
- CLAs
- Certain amino acids (especially glutamine and other essential amino acids)
Once threshold levels of these nutrients are reached, CCK is released and signals to your brain that you're not interested in eating more. At a subconscious level, your gut is informing your brain when you've ingested enough of what you need.
11. Glutamine: Immune Booster and Sugar Craving Killer
Glutamine deserves special attention. This amino acid:
- Bolsters the immune system (can increase killer cells)
- Triggers CCK release very potently
- Reduces sugar cravings
Dr. Huberman shares a story about a friend who's essentially addicted to sweets:
"He's a grown adult, but he eats candy and chocolate as if he was like a 14 year old kid hanging out at the local convenience store."
This friend started taking a teaspoon or two of glutamine several times throughout the day or whenever he craved sugar, and it significantly reduced his sugar cravings.
Important Notes on Glutamine
- Some people mix it with half and half to improve the chalky taste
- It can slightly increase blood sugar (especially in supplemental form)
- Caution: Many cancers and tumors like glutamine, so those with cancer predisposition should consult their doctor
- Can be obtained from foods like cottage cheese
12. Emulsifiers: The Hidden Danger in Processed Foods ⚠️
This is information that Dr. Huberman estimates 99.9% of people don't know about.
Emulsifiers are added to processed foods to extend shelf life. They allow certain chemical reactions to occur by bringing fatty molecules together with water molecules. They're found in candy bars, cereals, pastries, chips, and even some meats.
Why Emulsifiers Are Terrible
When you ingest emulsifiers:
- They strip away the mucosal lining of the gut
- They cause neurons that extend into the gut to retract deeper
- As a result, signals like CCK never get deployed
- The signals that shut down hunger are never triggered
- You want to eat far more of these processed foods
"In addition, if you then go from eating a highly processed food to non-highly processed foods, you're not able to measure the amounts of amino acids, sugars, and fatty acids in those foods as accurately."
The damage can be repaired if you stay away from processed foods, but the negative effects are quite real.
13. A Calorie Is NOT a Calorie
Dr. Huberman references a study by his colleague Chris Gardner at Stanford that found all diets (vegan, vegetarian, omnivore, intermittent fasting) produced equivalent weight loss when people adhered to them.
However, the processed foods research tells a different story. A study in Cell Metabolism took in-patient adults and gave them either ultra-processed or unprocessed diets for 14 days, matched for calories, sugar, fat, fiber, and macronutrients.
The results:
- People eating processed food ate much more
- Body weight changes were much greater
- These changes couldn't be accounted for by just increased calories
"The bottom line is that highly processed foods are just bad for you. They increase weight gain. They disrupt the lining of your gut in a way that disrupts things like CCK and proper satiety signals."
For more on this topic, Dr. Huberman recommends Dr. Robert Lustig's lecture (available on YouTube) about the history of processed foods and why the food industry started adding sugars and salts.
14. Insulin and Glucose: Understanding Blood Sugar Management
Insulin is secreted from the pancreas and is essential for:
- Shuttling glucose to appropriate tissues
- Keeping glucose levels in check
Blood Sugar Ranges
- Hypoglycemic: Too low
- Hyperglycemic: Too high
- Euglycemic (healthy range): About 70-100 nanograms per deciliter
Why Blood Sugar Management Matters
High glucose levels can damage and kill neurons, leading to:
- Peripheral neuropathies (loss of sensation in fingers, hands, feet)
- Diabetic retinopathies (blindness)
Types of Diabetes
- Type 1: No insulin production (requires insulin injections)
- Type 2: Insulin insensitivity (often associated with being overweight, usually manageable through weight management)
15. The Order You Eat Foods Matters
This is a practical gem: the sequence in which you consume macronutrients profoundly affects your blood glucose response.
Eating Carbohydrates First
- Blood glucose rises in a sharp spike
- This is why restaurants serve bread or chips before meals – steep increases in blood glucose promote the desire to consume more glucose
Eating Fibrous Foods First
- Blunts the release of glucose
- Even blunts the glucose increase from carbohydrates eaten afterward
- Leads to more steady blood sugar rise
- You'll achieve satiety earlier in the meal
"So what this means is, if you feel a lot of food related anxiety, or you feel you're one of these people that you can kind of sense like your blood sugar increasing very quickly... the key thing is to try and get some movement sometime around the meal."
The Ideal Order (for stable blood sugar)
- Fibrous vegetables first
- Protein second
- Carbohydrates last
16. Movement, Exercise, and GLUT4
Movement has an enormous impact on blood glucose management.
Before Eating
Any kind of exercise (even walking or jogging) before eating will dampen blood glucose levels through the release of GLUT4 (also called GLUT-4), which shuttles glucose toward muscle and glycogen stores and away from body fat stores.
After Eating
A 30-minute walk after a meal can significantly blunt blood glucose in beneficial ways.
"The higher intensity the movement, the greater the GLUT4 increase, and the more that the blood glucose will be blunted and you'll shuttle more of that to glycogen and muscle stores."
17. Why Sugar Stimulates Your Appetite
Understanding insulin and glucose explains why hidden sugars in processed foods are so problematic. Manufacturers add sugar you can't even taste because:
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