The findings explain why processed foods like doughnuts, chips and chocolate are particularly hard to resist. The study – published in Cell Metabolism – put 206 adults through brain scans while they were shown photographs of different fatty foods, sugary foods and foods featuring a combination of both. Not only did the fatty-carby foods elicit a greater response in the brain’s reward centre, participants also reported that they were willing to spend more money on those particular treats.
“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,” the study's senior author Dana Small said in a statement.
“Our participants were very accurate at estimating calories from fat and very poor at estimating calories from carbohydrate and our study shows that when both nutrients are combined, the brain seems to overestimate the energetic value of the food.”
The research demonstrates that our brains have two separate “systems” for assessing fatty foods and carb-heavy foods, and determining whether we want to eat them. However, when confronted with the combination of both – often found in a range of modern, processed foods that are rarely found in nature – our brain can't handle it because it hasn’t evolved to comprehend it.
These findings might also explain our current obesity epidemic.
"In the modern food environment that is rife with processed foods high in fat and carbohydrate — like donuts, French fries, chocolate bars, and potato chips — this reward potentiation may backfire to promote overeating and obesity,” Small said.