How does appetite regulation work?
Appetite regulation — Appetite is set by hormones from the gut and fat tissue acting on the hypothalamus, which weighs hunger against fullness and adjusts intake.
Appetite regulation works as a feedback loop: the gut, pancreas, and fat tissue release hormones that report on the last meal and on long-term energy stores, and the hypothalamus integrates those signals into a single drive to eat or to stop. Hunger is therefore a physiological output, not only a matter of will, which is why hormone-based drugs move food intake so effectively.
The control centre
The arcuate nucleus of the hypothalamus holds two opposing cell populations:
- AgRP/NPY neurons drive hunger. Ghrelin, released by an empty stomach, activates them.
- POMC neurons drive fullness. Leptin (from fat tissue) and gut hormones activate them. POMC is cleaved into α-melanocyte-stimulating hormone, which suppresses intake through the melanocortin-4 receptor.
Downstream, the brainstem and the reward circuits of the midbrain decide palatability — why appetite for a specific food can survive a full stomach.
The signals
| Signal | Source | Effect |
|---|---|---|
| Ghrelin | Stomach, before meals | Increases hunger |
| GLP-1 | Intestinal L-cells, after meals | Increases fullness, slows gastric emptying |
| GIP | Intestinal K-cells, after meals | Modulates insulin and fat handling |
| Peptide YY | Distal gut, after meals | Increases fullness |
| Cholecystokinin | Duodenum | Short-term meal termination |
| Leptin | Fat tissue | Reports long-term energy stores |
| Insulin | Pancreas | Reports nutrient availability |
Two of these explain most drug development in the area: incretin hormones and the melanocortin system.
Why weight loss is defended
Losing fat lowers leptin and raises ghrelin, and both changes push intake back up. Measured resting energy expenditure also falls more than body-mass loss alone predicts. This coordinated defence of the previous weight is the main reason diet-only results regress, and the main reason sustained drug effect requires sustained dosing.
Why peptides care
- Semaglutide and Tirzepatide act on the GLP-1 receptor (tirzepatide also on the GIP receptor) to increase fullness and slow gastric emptying. Both are FDA-approved.
- Retatrutide adds glucagon-receptor agonism to the same two targets and is still investigational.
- Melanotan II is a non-selective melanocortin agonist; its reported appetite suppression comes from MC3R/MC4R activity rather than from the incretin pathway. It has no regulatory approval anywhere.
Related concepts
Read incretin hormones for the gut side of the loop and GLP-1 receptor agonists for the drug class built on it.
Related peptides
See also
External links
This page was last updated on August 21, 2026, at 00:00 (UTC).
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