Carbs and fats, the brain is wired to love the combination

Why do some of us tend to overeat certain foods even when we are not hungry? Researchers from Yale University revealed how the carbohydrate-fat combination may light up the brain's reward system.

The study titled "Supra-Additive Effects of Combining Fat and Carbohydrate on Food Reward" was published in Cell Metabolism on June 14. Dana Small, director of the Modern Diet and Physiology Research Center at the university, was the senior author of the study. She explained how biological processes in our body carefully define values for food in order to make adaptive decisions.

"For example, a mouse should not risk running into the open and exposing itself to a predator if a food provides little energy," she said.

As many as 206 adult participants were shown photos of snacks that contained mostly fat, mostly sugar, and a combination of fat and carbs. They were asked to estimate how many calories were in the food items and also reveal how much they would pay for it.

"Surprisingly, foods containing fats and carbohydrates appear to signal their potential caloric loads to the brain via distinct mechanisms. Our participants were very accurate at estimating calories from fat and very poor at estimating calories from carbohydrate," explained Small.

Participants were also willing to pay more money for the fat-carb combination foods compared to the ones containing only fat or only carbohydrates. By using real-time brain scans, the research team observed how these combination foods could light neural circuits in the reward center of the brain.

The response was found to be greater when compared to sweeter snacks, more energy-dense food, or even a favorite food. "Liking has nothing to do with this response. Certain foods are harder to resist," Small said.

To understand why our brain works in such a way, the authors note how our ancestors mostly ate natural sources of food and did not consume snacks combining fats and carbs.

But today, our modern menus offer options ranging from pizza to doughnuts to other processed foods. Doughnuts, invented in 1847, are estimated to contain 11 grams of fat and 17 grams of carbohydrate. Since these foods have not been around for too long, the human brain may not have evolved to handle the reaction they trigger.

"The modern food environment proffers up nutrients in doses and combinations that do not exist in nature," the authors wrote. "This contrasts sharply with our ancestors’ diet composed mostly of woody plants and raw animal meat."

These findings may help experts understand how the reward system contributes to weight gain by promoting overeating, even if the person is not hungry. Recent studies highlighted increasing rates of obesity in the United States as well as the abundance of processed food options in the workplace.

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