WASHINGTON, June 14 (Xinhua) -- A study published on Thursday in the journal Cell Metabolism showed that the reward center of the brain valued foods high in both fat and carbohydrate more than foods containing only fat or only carbohydrate, lending a clue why modern people tend to gain weight.
The findings based on 206 adults supported the idea that those kinds of food, mostly processed food, could hijack our body's inborn signals governing food consumption.
"The biological process that regulates the association of foods with their nutritional value evolved to carefully define the value of a food so that organisms can make adaptive decisions," said the paper's senior author Dana Small, director of Yale University's Modern Diet and Physiology Research Center. "For example, a mouse should not risk running into the open and exposing itself to a predator if a food provides little energy."
"Food 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. Our study shows that when both nutrients are combined, the brain seems to overestimate the energetic value of the food," said Small.
In work that could help explain brain-body mechanisms underlying the genetic predisposition for obesity, eating in the absence of hunger, and difficulty losing or keeping off excess weight, Small and colleagues in Germany, Switzerland, and Canada looked at the neural response to food cues.
Test subjects underwent brain scans while being shown photographs of familiar snacks containing mostly fat, mostly sugar, and a combination of fat and carbohydrates.
According to the study, allocated a limited amount of money to bid on their first-choice foods, subjects were willing to pay more for foods that combined fat and carbohydrates.
The fat-carbohydrate combo was found to light up neural circuits in the reward center of the brain more than a favorite food, a potentially sweeter or more energy-dense food, or a larger portion size.
Researchers said that the hunter-gatherer ancestors ate mostly woody plants and animal meat, and after the domestication of plants and animals and the development of grain and dairy production around 12,000 years ago, opportunities to consume fat and carbohydrates together increased, but processed foods like donuts, which could contain 11 grams of fat and 17 grams of carbohydrate, have only been around for 150 years, not long enough for us to evolve a new brain response to them.
They suggested that human beings' past experience with the nutritive properties of carbohydrate could release dopamine in the brain through an as-yet-unknown metabolic signal and these kinds of signals seemed to help regulate what and how much we eat.
The researchers theorized that the simultaneous activation of fat and carbohydrate signaling pathways launched an effect that human physiology has not evolved to handle.
Consistent with this suggestion, rodents given access to fat alone or carbohydrate alone regulate their total daily caloric intake and body weight. But given unrestricted access to fat and carbohydrates, they quickly gain weight. Enditem
