Does your stomach really expand and shrink, depending on how much you eat?
Yes and no: It does expand every time you eat a meal (and contracts again after you’re done digesting), but it won’t shrink if you diet or fast. The organ has an average resting volume of about 50 ml (.01 gallon), but after a normal meal it expands to about 1 liter (0.26 gallon). If really pushed, the stomach can accommodate up to 4 liters (an entire gallon) of food.
So what if you really push it? Say you go for the tasting menu one night and end up eating twice as much as you normally do at dinner—will your stomach permanently expand a little bit? Nah. It will probably remain distended for longer than usual, because rich, fatty foods slow digestion and thus stay in the stomach longer than leaner fare. And when high fat content is coupled with a large volume of food, your stomach definitely has more work to do than it normally would (plus, it needs more acids and enzymes to do the job, and these add more volume). Still, we’re not talking days here; typically, the stomach is fully empty and “deflated” anywhere from three to five hours after a meal.
Except if you’re a competitive eater, routinely testing your stomach’s 1-gallon limit by eating massive amounts of food. In that case, says Dr. Carol Semrad, a gastroenterologist at the University of Chicago, “the stomach may not get a chance to completely empty and therefore stays enlarged—and this may account for [competitive eaters’] ability to chronically eat a large amount of food without stomach rupture.”
On the “shrinking” side, the only thing that will permanently reduce the size of your stomach in its deflated state is gastric bypass surgery; dietary changes don’t alter the physical size of the organ. “If we eat less, we get used to eating less,” says David Levitsky, a professor of nutrition and psychology at Cornell University. “But the change is behavioral—it’s not due to actual shrinkage.”