People like food because it contains calories they need to survive. However, researchers from The John B Pierce Laboratory and Yale have discovered an interesting twist to the basic biology story: Calories trigger responses in areas of the brain that control eating behavior independently of how much the subject likes the flavor.
“The implication is that calories don’t need to increase liking to influence our eating,” said Dana Small, associate professor of psychiatry, associate fellow of the Pierce Laboratory, and senior author of the study to be published in the May 20 edition of the journal Current Biology.
The findings shed light on how food cues trigger eating, insights that can help explain overeating and obesity, say the researchers.
The Yale team was interested in teasing out the signals that allow the brain to assess the nutritional value of the food.
Fourteen subjects were tested for preferences for flavors of novel drinks without calories. Later, calories were added to one of the drinks by adding an undetectable carbohydrate.
The subjects consumed this flavored beverage and one without calories repeatedly over three weeks. The effect of consuming these drinks on blood glucose was also measured. Following this conditioning, subjects’ brains were then scanned as they sampled non-caloric versions of both flavored drinks. As predicted, participants liked the calorie-paired flavor. The team found that a change in blood glucose produced by drinking the flavor that had once contained calories strongly predicted responses in regions of the brain known to guide feeding.
“What was striking was that this happened completely independently from changes in liking,” Small said.
This helps explain why eating — and over-eating — are often unrelated to how much a person likes the food, say the researchers. It also suggests that individuals with altered glucose metabolism, like people with diabetes, will be more susceptible to food cues because they have increased glucose responses to food.
Ivan E de Araujo was lead author of the paper. Other Yale authors are Tammy Lin and Maria G. Veldhuizen.
The National Institute of Diabetes and Digestive and Kidney Diseases funded the study.