Consuming a protein-rich drink before a meal leads to a 19% reduction in the amount of food eaten during that meal in healthy young men.

When healthy young men consume protein before a meal and fat is delivered directly to the upper intestine, the total amount of food they eat is not lower than when they consume protein alone. This suggests the two stimuli affect fullness independently, not together.

Consuming a protein-rich drink before a meal reduces feelings of hunger and increases fullness in healthy young men, but introducing fat directly into the upper intestine does not significantly affect these sensations, suggesting that protein's effect on fullness comes from signals originating in the stomach or nerves rather than hormones.

When the proportion of protein in the diet is lowered from 15% to 10% of total calories, people tend to eat more total food to maintain their protein intake, resulting in higher overall energy consumption.

When people eat a meal with less protein than usual, they tend to eat more total calories that day — and this pattern holds up even when accounting for other factors.

The day after eating a meal with less protein than usual, people tend to eat about 60 fewer calories than normal.