satiety
Satiety is the comfortable “I'm done” feeling that brings a meal to an end and keeps you from eating again for a while. Rather than a single switch, it builds up like a tide — beginning while you are still eating and continuing for hours after, as the gut digests and reports back to the brain.
Physiologically, satiety has two parts. Satiation is the within-meal process that makes you put down your fork, driven by stomach stretch and rapid gut hormone release such as CCK. Satiety proper is the longer between-meal suppression of hunger, supported by hormones like GLP-1 and PYY from the intestine and by background signals such as leptin and insulin reflecting overall energy stores. These messages converge on hypothalamic and brainstem circuits.
Foods differ in how much satiety they produce per calorie: protein and fiber are strongly satiating, while highly processed, energy-dense foods tend to be eaten in excess before fullness registers. Many modern weight-loss drugs work largely by amplifying these natural satiety signals.
There is a built-in lag: the brain takes roughly 15–20 minutes to register fullness, which is why eating slowly tends to reduce overall intake.