When healthy older adults receive a specific dose of the hormone CCK-8 through an IV, they eat about 11% less food afterward, no matter what they ate before.

A two-week high-fat diet does not change how effectively the hormone CCK-8 reduces hunger in healthy older adults, as measured by how much food they eat afterward.

In older adults, eating a high-fat diet does not reduce the ability of the hormone cholecystokinin-8 to signal fullness after eating.

A 14-day high-fat diet increases total calorie intake by about 41% in healthy older adults, but does not change baseline levels of the hormone cholecystokinin or its ability to reduce appetite when administered externally.

When young people eat, their body releases more of the fullness hormone than older people do, which might help them feel satisfied faster.

Older people, no matter how well they eat, have more of a fullness hormone in their blood than young people—but that doesn’t explain why some older people eat less.