Northwest Arkansas Democrat-Gazette
Why do we have room for dessert?
One of the more curious phenomena during the holiday season is how we can feel completely full after a big meal, yet somehow always find room for dessert.
Our ability to eat a ridiculous amount of food on Thanksgiving and other holidays is related to the sheer variety of foods typically offered in a feast. Variety excites the appetite.
This “variety effect” is an evolutionary adaptation that served us well during pre-buffet times. Imagine if your ancestors binged on buffalo meat and then stumbled across a patch of ripe berries — but everyone was too full to eat them. Skipping dessert in that scenario would mean missing out on a stash of important nutrients. (And if that had happened, you probably wouldn’t be reading this now.)
The mechanism that allows us to make room for dessert is called sensory specific satiety, which means that the body has different limits for different foods as a way to help ensure a balanced intake of nutrients. Barbara Rolls, a professor and the director of the Laboratory for the Study of Human Ingestive Behavior at Pennsylvania State University, has been studying sensory specific satiety since the early 1980s.
“It’s the reason most of us manage to eat a balanced diet even if we don’t have nutritional knowledge,” Rolls said. “Variety is our friend in terms of nutritional balance.”
Over the years, Rolls has asked countless adults and children to fill up on savory foods such as chicken or sausages. When offered a second serving, study subjects were often too full to eat much more. But when they were then offered cookies, bananas or raisins, they always had room for another bite.
“It’s a change in your hedonic response to the food you’ve just eaten,” said Rolls, referring to the pleasure we get from eating. “If you’ve had a lot of salty and savory foods, the sweet foods might get more pleasant.”
Fast-forward to the modern feast, and you begin to understand why at this time of year so many of us become eating machines. After filling up on a few rounds of prime rib, latkes or other holiday favorites, chances are you’ll feel quite full. But when the pie with whipped cream or cheesecake
comes around, your brain will sense an entirely different kind of food, and suddenly, you’ll find yourself reaching for dessert.
But don’t worry. Although sensory specific satiety allows you to keep eating new foods, eventually your body will tell you to stop eating. After about 1,500 calories in one sitting, the gut releases a hormone that causes nausea.
Notably, the satiety signal is particularly strong in children and diminishes with age. In studies by Rolls, children were allowed to eat unlimited quantities of M&M’s. But once they were full, they had a strong response to being offered more. “These little kids said, ‘These taste yucky — I don’t like them anymore,’” Rolls said. “We’d never seen as strong a response in adult subjects.”
The reason for the pronounced difference in response by age isn’t clear, Rolls said. It may have to do with a natural decline in sense of smell and appetite as we get older. Or it could be that a lifetime of eating highly processed foods interferes with our natural satiety signals.
The main consequence of eating a big meal is the need to unbutton your pants. (Recently, on the “Milk Street” podcast, culinary historian Yolanda Shoshana recommended a “pajama” Thanksgiving to solve that problem. Find that at arkansasonline. com/ 1213milk.) Indigestion and flatulence are also common hazards of feasting. In rare cases, the extra digestive workload can temporarily raise the risk for a heart attack or gallbladder problems, so people with underlying cardiovascular disease should take care to avoid overdoing it.
The biggest downside of this variety effect is that food makers have taken notice. It’s the reason marketers have created variety packs and bundle multiple foods together in “value meals.”
“It’s of great interest to food companies who want to sell you more food and get you to eat more food,” Rolls said. “But you can also engineer your eating environment to have this work for you. Nobody wants to eat a half a plate of broccoli, but if you fill half your plate with a variety of vegetables and fruits, in that case, variety is a good thing.”