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It's happened to all of us: Dinner's over and you're stuffed. But then someone brings out the pie and ice cream. And while a moment ago you couldn't have eaten another bite, suddenly… well, of course you can find room for a little pie.

And it's actually kind of true that you always have room for dessert. It has to do with how our bodies evolved—long before dessert existed the way we know now. But once you understand why you always have room for dessert, you'll see how you can use this weird quirk of your appetite to your advantage.

When it comes to our appetites in general, humans and other animals tend to get less pleasure out of eating something the more they eat it. This is called sensory specific satiety, and it's an example of habituation: Whenever you encounter some stimulus over and over again, your response to it goes down. It's like when you hear a great new song for the first time, and you love it—but then after a few months of hearing it on the radio, you're just completely over it.

Our brains react the same way to food. At first, a new food is really rewarding… but eventually, your brain gets tired of it. And neuroscientists have actually watched that happen in real time.

In a 2001 study published in the journal Brain, experimenters gave nine subjects a series of chocolates and scanned their brains while they ate them. After every piece, the subjects rated how much they enjoyed the snack and how much they wanted another. Even though they were eating the same kind of chocolate each time, both of these ratings kept going down with every passing piece.

Not only that, but their brain activity changed, too — specifically in the orbitofrontal cortex, which processes sensory and emotional information. In one spot, there was less activity over time, suggesting it was reacting to how rewarding the chocolate was. But in another spot there was more activity, suggesting that it was a sign of an increased sense of revulsion or punishment.

To chocolate. Because it had just had enough. And a number of studies have shown similar results:.

When people fill up on one thing, even if it's something they like, they begin to feel repulsed by it. But even if they can't stomach any more of that one thing, their brains don't have the same reaction to other food. So when it comes to finding room for dessert, something similar seems to be going on.

See, if you've had a well-balanced meal, you've probably filled up on vegetables, proteins, and complex carbs—so your body's had enough of that. But dessert is different: It doesn't have a lot of those things, and it usually has a lot more sugar. And your brain's not tired of that yet, so suddenly, you're not as full as you thought.

As weird as that seems, it might have been kind of an advantage from an evolutionary perspective. We don't know exactly why we evolved this trait, but in the past, the fact that we sought out variety might have meant we were better at eating a balanced diet, and weren't missing key nutrients. There's also one other factor that makes it especially easy to make room for dessert:.

Dessert just doesn't fill you up the same way as other food. Typically, you know you're hungry because your stomach releases a hormone called ghrelin, which alerts the brain that you need food. Then as you eat, the amount of ghrelin in your blood goes down, and you start to feel less hungry.

But that change in the amount of ghrelin depends on what you've eaten. Complex carbs and proteins cause a significant drop, but sugar barely changes your ghrelin level at all. Eating just simple sugars is almost as insignificant to your appetite as drinking water.

And let's face it—most desserts are basically sugar. So, not only is your brain not tired of it, but as you eat, dessert just doesn't fill you up as much. Your body does have other ways of informing you that it's full, like by using special receptors to sense how stretched or contracted your stomach is, so eventually you would feel full no matter what.

But if you're still feeling betrayed by your brain for letting you eat more dessert than you intended, think about it this way: You can also use all this to your advantage. For example, sensory-specific satiety does make it easier to squeeze in dessert, but you can also take advantage of it to squeeze other foods into your diet. Like, maybe you bought something healthy for snacking, like a bag of almonds, but now you're just tired of those, and the junk food is calling to you.

Well, if you have a variety of healthy snacks, you have a better chance of actually wanting to eat them. In a 2013 study in American Journal of Clinical Nutrition, researchers tested a similar thing on kids. During preschool snack time, they put out different fruits and vegetables and tracked what the children ate.

If they just put out one kind of fruit or vegetable, about 70% of kids took a snack. But if they put out a variety, 94% did—and they ate about three more pieces of fruit on average. So if you've ever struggled to get a picky kid to eat some vegetables, variety might help!

And when it is time for dessert, if you're trying to scale back, you can try avoiding eating sugars on their own. Like, you could have your ice cream with fruit or add oats to your cookies—and it may help you feel fuller for longer. If nothing else, it's good to know that it's not your imagination: Your body really does react a little differently to dessert at the end of a meal.

And at the very least, knowing how it works might help you trick yourself to eating a little better. The way we evolved alongside our food continues to shape our relationship with it today, and if you're interested in learning more about that, you might like the book “The Way We. Eat Now,” which is available on Blinkist.

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