Everyone has heard, at some point in their life, that eating less will make your stomach shrink. And, in turn, eating more will make your stomach stretch and expand. But is this true? Sort of, but it isn’t as easy as it sounds, Dr. Kyle Staller, a Gastroenterologist at Massachusetts General Hospital. says “The stomach is an organ that’s made to stretch,” he says.

“When you eat food, it doesn’t just plop into a big bag,” he explains. When first entering the stomach, the food goes into something called the fundus, which is in the upper part of your stomach. It stretches out as much as it can to accommodate the food you have just eaten. Everyone has different thresholds when it comes to their fundus, however. This explains why you may actually be able to always have room for dessert, but not another entrée, you’re actually working with less volume.

Your stomach may stretch, but in only about 4 or less hours it will return to its normal size, due to your food moving into your small intestine. But if you’re regularly eating more than usual, and at a faster pace than your stomach can signal to your brain that you’re full, it’s possible for you to train your fundus to accommodate more food.

“On the flip side, if you don’t eat as much as usual for a while (like when you’re trying to lose weight), you stomach won’t necessarily shrink, but it won’t be able to fit in as much food as before right away,” Staller says. That explains why you tend to feel fuller faster when you eat a big meal after dieting. “It’s like your muscles—you’ll be able to do less and less each time when you don’t use it,” Staller explains.

So, next time you want to make room when you spot a tasty-looking flan on the dessert menu, know this: Your fundus is probably up for it—and provided you pick up your clean-eating habits in the next morning, it’ll shrink back to normal in no time.