Logic dictates that we load up our one stomach with one meal, and we’re done. For a few hours, at least. But as many of us know, it doesn’t quite work out that way. When it comes to dessert, it’s almost as if we develop a second stomach. You might think it’s a lack of willpower, but according to Michelle Spear, a professor of anatomy at the University of Bristol, that “second stomach” you rapidly developed when you heard there was cake yet to come is the result of brain chemistry and social conditioning working in tandem exactly as designed.
Writing in The Conversation, Spear describes the exact feeling a lot of us experience in the gauntlet of massive holiday meals that end every year. Specifically, she examines them through the lens of the Japanese word “betsubara,” or “separate stomach.”
The Japanese have not discovered a second cow-like stomach in humans. The term is a silly colloquial way of describing the sudden and seemingly inexplicable desire to find room for dessert when there previously was no room for anything else. The sensation is real, Spear argues, but there’s nothing especially fascinating going on in our stomachs that makes room for sweet treats.
While our stomachs find a way to accommodate any desserts we put in them, our brains play a bigger role than you’d think.
The human stomach isn’t a rigid container that hits max capacity when it fills to the brim. It’s kind of elastic-y. When you eat, it relaxes through a process called gastric accommodation and expands without dramatically increasing pressure. Dessert is usually soft and mushy, low on fiber and protein, so it doesn’t take up a whole lot of space and doesn’t require much mechanical effort to digest. Ice cream is easier to make room for than a second steak, for instance.
Hunger doesn’t shut off once you’re physically full. What takes over is “hedonic hunger,” the urge to eat for pleasure rather than necessity. This is where your brain takes over. Desserts activate the brain’s reward system, releasing dopamine and temporarily quieting signals that tell your stomach you’ve had enough.
You may not need dessert, but your brain wants it — and it will perform all the complicated mental gymnastics necessary to convince you that it’s not just a good idea, but the best idea.
As you eat one type of food, your brain gradually finds it less rewarding. Switching to something sweet or creamy or both refreshes that response. That’s why someone who can’t finish their main course might still be able to find a little room for dessert. Their bellies may not be full, exactly, but they may be experiencing a kind of overstuffed sensory response that needs a little novelty to reset interest.
Fullness signals from hormones like GLP-1 and peptide YY take 20 to 40 minutes to fully kick in. Dessert decisions often happen before that system has caught up. Restaurants know this instinctively, offering menus while our natural reward system can still be exploited. Add cultural aspects, like how dessert is often seen as a celebratory act or part of a ritual, and then toss in a little bit of emotional eating when we need a sugary pick-me-up, and it’s easy to understand why, especially during the holidays, there’s always room for dessert.
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