Calories Trigger Overeating, Not Actual Taste

NEW HAVEN, Conn.Foods with calories trigger more brain responses linked to eating than calorie-free foods do, regardless of whether they taste better, according to a new study published in the journal Current Biology. The findings suggest there are two unrelated brain circuits that kick into gear when people eatone is related to consciously liking flavors, while the other responds to glucose in the blood.

Previous animal studies have found that mice, rats, and fruit flies are able to sense nutrition independently of taste. Even when researchers genetically engineered lab animals not to be able to taste sweetness, they learn to prefer mixtures containing real sugar instead of artificial sweetener.

Researchers at Yale University had study participants drink artificially flavored drinks. Some of the drinks were calorie-free, while others contained maltodextrin, a carbohydrate that people cant taste, but still has calories. In a series of experiments, the researchers found that over three weeks time, people come to like the flavor paired with maltodextrin more, even though they couldnt taste the added carbohydrate. Still, they only increased their liking from mildly pleasant" at the start of the study to moderately pleasant" at the end of the study.

The researchers saw a larger effect when they took functional magnetic resonance imaging (MRI) scans of peoples brains while they sipped the different flavors. Although they gave everyone 112.5 calories worth of maltodextrin in their caloric drinks, different people have different metabolisms, so the blood sugar levels differed after drinking the maltodextrin drink. The researchers saw that two regions in the brain, the hypothalamus and the nucleus accumbens, responded to the drinks in such a way that people with more blood glucose after drinking had more of a brain response. Meanwhile, the hypothalamus and nucleus accumbens responses werent related to how much people said they liked their drinks.

The researchers concluded people who overeat dont necessarily like calorie-dense foods more. Instead, some people may be more at risk for overeating because their blood glucose levelsand brainsare reacting more strongly than other peoples.