The Yale University finding sheds light on how the processed food industry cashes in on the human craving for unhealthy diets.
Senior author Prof Dana Small, director of the Modern Diet and Physiology Research Centre at Yale University in the USA, said: "Surprisingly, foods containing fats and carbohydrates appear to signal their potential caloric loads to the brain via distinct mechanisms".
The study points out foods high in both carbohydrates and fats rarely exist in nature, with the exception of breast milk.
A study of 206 adults, that appeared June 14 in the journal Cell Metabolism, supports the idea that these kinds of foods hijack our body's inborn signals governing food consumption.
"These foods that have both fat and carbohydrate are tricking this ancient mechanism, so the response is larger than it should be for the amount of energy that's actually there", Small said.
Results showed that the neurons at the reward centres of the brain lit up when the fat and carbohydrate rich foods were shown. The participants were asked if they would spend more money to buy these unhealthy options and majority said they would.
Our hunter-gatherer ancestors ate mostly woody plants and animal meat, the researchers noted.
Study leader Dana Small, director of Yale's Modern Diet and Physiology Research Center, and her colleagues set out to perform an experiment using real-time brain scans. "By contrast, it is very common for processed foods to have high fat and high carbohydrate loads".
The snacks were either high in carbs (lollipops or candy), high in fats (meatballs or cheeses), or high in both (cookies or cakes), Small said.
To know about it, the researchers of the study took MRI scans of the brains of participants invited for the study while showing them pictures of various foods.
It's believed that our past relationship with carbohydrates influences the release of dopamine in the brain when presented with certain foods. These kinds of signals seem to help regulate what and how much we eat. And since farming methods developed around 12,000 years ago, it has become easier to produce fats and carbohydrates both separately and together.
"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".
"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", she continued.
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