When fat is delivered directly into the small intestine of healthy young adults at a rate of 6 grams per hour, it triggers the release of a hormone called cholecystokinin, which leads to increased feelings of fullness and reduced eating afterward. Blocking this hormone reduces those effects.

We analyzed one assertion on this topic and found that delivering fat directly into the small intestine of young adults at 6 grams per hour increases the release of cholecystokinin, a hormone involved in digestion and appetite control. This increase was linked to stronger feelings of fullness and lower food intake afterward. When cholecystokinin was blocked, those effects weakened [1]. What we’ve found so far suggests that fat in the small intestine can signal fullness through this hormone pathway in healthy young adults. The mechanism appears consistent: fat triggers cholecystokinin, which then reduces how much people eat. There were no studies in our review that contradicted this pattern. This does not mean fat always reduces hunger in every situation — the effect was observed under controlled conditions using direct infusion, not through normal eating. We also don’t know if this works the same way in older adults, people with metabolic conditions, or with different fat amounts. The evidence we’ve reviewed is limited to one specific setup and one group of people. For now, the pattern points to cholecystokinin playing a role in how the gut responds to fat, and that response may help reduce eating. But this is just one piece of a much larger picture. In everyday terms: if fat reaches your small intestine, your body may naturally signal you to stop eating — but this doesn’t mean eating more fat will make you less hungry in real life. The way fat is delivered matters.