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.

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

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.

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