Once we’ve started eating, what makes us stop? This is in part influenced by satiation — the perception of fullness you get during a meal that causes you to stop eating. (Satiety is sometimes used interchangeably with satiation, but the terms aren’t the same. Satiety is your perception of satisfaction, or reduced interest in food, between meals; satiation is your perception of fullness during a meal.) When we eat a meal, two physiological factors work together to tell us to put down our fork and call it quits: gastric distension and hormonal satiation.

Gastric distension When empty, your stomach can only hold about 50 mL. When you eat, the stomach can expand to hold 1000 mL (1 liter), or at the extreme end, 4000 mL (4 liters or 1 gallon). Your stomach is designed to stretch and expand, aka gastric distension. Your stomach is also designed to tell your brain about how much stretching is happening. As your stomach expands to accommodate the incoming food, neurons in your stomach send this message to your brain via the vagus nerve, which runs from your head to your abdomen.