Satiety Hormones Library: The Signals That Make You Full

For every signal that drives you to seek food, the body keeps a counterweight that tells you to stop. Hunger gets the attention — it is loud, urgent and easy to name — but fullness is the more crowded side of the ledger. Where appetite is pushed up by essentially one major hormone, ghrelin, the brake is applied by a whole committee of them, released in sequence as a meal moves through the body. Together they form the satiety system: the chemical machinery that decides when enough is enough.

This library is a reference to that committee. It covers the seven hormones that do most of the satiety work — cholecystokinin (CCK), GLP-1, peptide YY (PYY), leptin, amylin, oxyntomodulin and insulin — and for each it sets out four things: where it is made, what triggers its release, what it actually does, and over what timescale. Some act within minutes of the first mouthful; others report on energy reserves built up over weeks. A few have become the templates for modern weight-loss drugs. For the broader picture of how these signals are read by the brain, our companion hunger hormones guide sets satiety against the hunger side of the system.

A note on terms. Satiation is the process that brings a single meal to an end; satiety is the longer sense of fullness that suppresses the next one. Most of the hormones below contribute to both, and the distinction matters more in the laboratory than at the table — though if you want it teased apart, see our piece on satiety versus fullness. What unites every hormone here is direction of travel: each one, in its own way, says stop.

CCK (cholecystokinin): the first brake

CCK is the earliest satiety signal in a meal — the first hand raised to call a halt. It was also the first gut hormone shown to do so. In 1973, James Gibbs and Gerard Smith, working with Robert Young, reported in the Journal of Comparative Physiology and Psychology that injecting CCK into rats made them stop eating sooner and take smaller meals, in a dose-related way, without simply making them ill. It was the founding demonstration that a hormone from the gut could end a meal, and it launched the entire field of gut-derived satiety.

Where it is made: by I-cells in the lining of the duodenum and upper small intestine. Trigger: the arrival of fat and protein in the upper gut as the stomach empties. Action: CCK slows gastric emptying, prompts the gallbladder to release bile and the pancreas to release digestive enzymes, and — most relevant here — signals through the vagus nerve to the brainstem that a meal is underway and can be wound down.

Timescale: fast and short. CCK rises within about fifteen minutes of eating and fades quickly, which is why it governs the size of the meal in front of you rather than your appetite hours later. Drug relevance: CCK itself has proved hard to turn into a medicine — its action is too brief, and sustained stimulation breeds tolerance — but it remains the proof of concept on which later, longer-acting hormones built. It works closely alongside GLP-1 and PYY, the trio explored in satiety hormones: GLP-1, PYY and CCK.

GLP-1 (glucagon-like peptide-1): the signal behind the medicines

GLP-1 is the satiety hormone that reshaped obesity medicine. It is the molecule that semaglutide and tirzepatide are engineered to imitate, and understanding what it does naturally is the clearest route to understanding why those drugs work. Daniel Drucker, whose 2018 review in Cell Metabolism remains a standard reference, helped establish its many-handed profile over a long career.

Where it is made: by L-cells in the lower small intestine and colon. Trigger: nutrients reaching the distal gut after a meal. Action: GLP-1 does several jobs at once. It prompts the pancreas to release insulin, but only when blood glucose is high — which makes it safe from a hypoglycaemia standpoint; it slows the rate at which the stomach empties, prolonging fullness; and it acts directly on the appetite centres of the brain to enhance satiety and dampen the reward pull of food.

Timescale: GLP-1 begins rising within ten to fifteen minutes of eating and stays elevated for an hour or more — but the native hormone is destroyed within about two minutes once released, which is the whole problem the drugs were built to solve. Drug relevance: central. GLP-1 receptor agonists are modified so the body cannot break them down quickly — semaglutide lasts roughly a week — supplying a steady satiety signal the brain reads as well-fed. Our explainers on how GLP-1 influences satiety and how satiety signals work go further into the mechanism.

PYY (peptide YY): the post-meal brake

PYY is GLP-1's close companion — released from the same cells, at the same time, in the same direction. If CCK opens the meal's closing argument, PYY sustains it over the following hour or two. In 2002, Rachel Batterham and Stephen Bloom's group at Imperial College London showed in Nature that infusing the active form, PYY(3-36), into healthy volunteers cut how much they ate at a later buffet by roughly a third — a striking demonstration that a single gut hormone could measurably curb intake in people.

Where it is made: by the L-cells of the lower small intestine and colon, the same population that produces GLP-1. Trigger: the calorie content of a meal, and especially its protein and fat. Action: PYY acts on the gut and on the brain's appetite centres to reduce the desire to eat more — a meal-termination brake in the plainest sense.

Timescale: PYY climbs over the one to two hours after eating and stays raised for several hours, bridging the gap between one meal and the next. Drug relevance: a long-standing target. Batterham's group also found that people with obesity release less PYY after a meal and feel correspondingly less full, which is partly why high-protein meals — which drive a stronger PYY response — tend to satisfy for longer, a theme picked up in why some foods fill you up.

Leptin: the long-term fuel gauge

If the gut hormones report on the meal in front of you, leptin reports on the energy you have banked. It is the body's fuel gauge — and its discovery in 1994, by Jeffrey Friedman and colleagues at Rockefeller University, transformed how obesity was understood. Tracking down the gene behind a strain of enormously obese mice, they found it encoded a hormone made by fat cells; replacing the missing hormone in those mice stopped their overeating almost overnight. They named it leptin, from the Greek leptos, meaning thin.

Where it is made: by white adipose (fat) tissue, in rough proportion to how much fat you carry. Trigger: total fat mass — leptin is a slow background signal, not a meal-by-meal one. Action: it acts on the hypothalamus to quieten hunger-driving neurons and stimulate fullness-driving ones, biasing the system toward satiety when energy stores are healthy.

Timescale: the slowest signal here — days to weeks, tracking the size of fat stores rather than the timing of meals. Drug relevance: a cautionary tale. Giving extra leptin to people with common obesity barely curbs appetite, because most already have high levels; what fails is the brain's ability to hear the signal, a state called leptin resistance covered in leptin resistance and never feeling full. Leptin replacement does work, dramatically, in the rare people born unable to make it.

Amylin: insulin's quiet partner

Amylin is the least familiar hormone on this list, yet it travels everywhere with one of the best known. It is co-secreted with insulin from the same pancreatic cells, in a fixed ratio, and adds a satiety dimension that insulin alone lacks. Because the natural molecule clumps into fibrils — making it useless as a drug — a stabilised analogue, pramlintide, was engineered and approved in 2005 as an add-on to mealtime insulin in diabetes.

Where it is made: by the beta cells of the pancreas, alongside insulin. Trigger: rising blood glucose after a meal, the same stimulus that releases insulin. Action: amylin slows gastric emptying, suppresses the post-meal release of glucagon, and signals through the brainstem — the area postrema in particular — to promote satiety and limit meal size.

Timescale: meal-related, rising and falling with each meal in step with insulin. Drug relevance: growing fast. Pramlintide reduces food intake in people with and without diabetes, and amylin-based agents — alone and paired with GLP-1 drugs — are now among the most closely watched candidates in obesity medicine, precisely because they hit a different satiety pathway from GLP-1.

Oxyntomodulin: the dual-action signal

Oxyntomodulin is something of a hybrid, and that is the source of its appeal. It is cut from the same precursor protein as GLP-1 and behaves like a two-in-one molecule, switching on both the GLP-1 receptor and the glucagon receptor. The result is a signal that both lowers appetite and, unusually, raises the rate at which the body burns energy. In a 2005 randomised trial in Diabetes, Katie Wynne and colleagues at Imperial College London showed that four weeks of self-administered oxyntomodulin reduced both food intake and body weight in overweight and obese volunteers.

Where it is made: by the L-cells of the lower gut, alongside GLP-1 and PYY. Trigger: food intake, in proportion to the calories consumed. Action: it reduces appetite through the GLP-1 receptor while increasing energy expenditure through the glucagon receptor — attacking the energy balance from both sides at once.

Timescale: meal-related, like the other L-cell hormones, and similarly short-lived in its native form. Drug relevance: considerable. Native oxyntomodulin is degraded too quickly to be a practical drug, but its dual GLP-1/glucagon design has inspired a class of long-acting "twincretin" and triple-agonist molecules now in advanced development for obesity.

Insulin: the metabolic hormone with an appetite role

Insulin is famous for controlling blood sugar, but it doubles as a satiety signal — and, like leptin, it is one the brain can stop hearing. The two are often discussed together because they play similar central roles: both report on the body's energy state and both are blunted in obesity.

Where it is made: by the beta cells of the pancreas. Trigger: rising blood glucose after a meal. Action: insulin's day job is to move glucose out of the blood and into cells for use or storage. But it also crosses into the brain, where — like leptin — it acts on the hypothalamus as an adiposity signal, reporting on energy state and nudging appetite downward.

Timescale: dual. Insulin tracks blood glucose minute to minute, yet its average level over time also reflects body fat, giving it both a fast and a slow character. Drug relevance: indirect but important. In insulin resistance — common in obesity and type 2 diabetes — cells respond poorly, the pancreas compensates by releasing more, and the chronically high levels both promote fat storage and appear to blunt insulin's own appetite-lowering message in the brain. As reviewed by David Cummings and Joost Overduin in their 2007 survey of gut and pancreatic satiety signals, insulin sits at the junction of metabolism and appetite rather than belonging cleanly to either.

The satiety hormones at a glance

The seven hormones below all push in the same direction — toward ending a meal or curbing the next one — but they do so on very different clocks and through different routes. The table summarises where each is made, what triggers it, and what it does; the body of this library fills in the timescale and drug relevance for each.

What the table cannot show is how they work as an ensemble. CCK opens proceedings within minutes; GLP-1, PYY and oxyntomodulin build the case over the following hour or two; amylin and insulin track each meal while also reporting on the longer term; and leptin sits in the background, gauging the fat reserves accumulated over weeks. All of them converge on the same small regions of the brain — chiefly the hypothalamus and the brainstem — where their combined message is weighed against the single, insistent hunger signal of ghrelin. Fullness, in other words, is not one thing arriving but a chorus reaching the brain at once. For how that chorus is decoded, see the broader how satiety signals work.

Why the satiety system matters for weight

The reason this library is more than a curiosity is what happens to these signals in obesity and after weight loss. Several of them — the meal-time rise in GLP-1 and PYY, the brain's response to leptin and insulin — are blunted in people with obesity, so the after-eating brake arrives weaker than it should. And after dieting, the satiety hormones as a group tend to stay suppressed for a long time, while hunger signalling climbs. The body reads weight loss as a threat and defends its former size by easing off the brakes and pressing the accelerator.

This is the insight that modern weight-loss medicine is built on. Rather than asking willpower to fight a hormonal environment tilted toward eating, GLP-1 receptor agonists and their successors supply a satiety signal strong and steady enough that the brain reads the body as well-fed even while a person eats less. The amylin and oxyntomodulin programmes now in development aim to do the same through parallel pathways, on the logic that hitting several satiety routes at once may work better than leaning on one. For how these threads come together across the wider topic, see the hunger and satiety guide, the hunger and satiety hub, and the broader appetite and hunger collection.