A new neuroimaging study suggests that our brain evaluates food based on caloric density, even when we're not conscious of how many calories something contains, which is perhaps why many of us prefer junk food.

Researchers from the Montreal Neurological Institute and Hospital of McGill University in Canada, have discovered that our brain subconsciously makes decisions on what food to eat based on the food's calorie content. The findings which are published in the journal Psychological Science, could explain why many people choose high calorie foods.

"Earlier studies found that children and adults tend to choose high-calorie food" said Alain Dagher, neurologist and lead author of the study, in a press release. "The easy availability and low cost of high-calorie food has been blamed for the rise in obesity. Their consumption is largely governed by the anticipated effects of these foods, which are likely learned through experience."

The study involved a group of participants who were asked to rate pictures of familiar foods based on which they would like to consume. They were then asked to estimate the calorie content of each food item. Observations showed that the participants preferred high caloric food, even though they were not able to accurately indicate the calorie content.

The team also performed brain scans on the participants while they were evaluating the food images which supported the observations. The scan results showed that activity in the ventromedial prefrontal cortex - an area of the brain that is involved in decision making - was correlated with the foods' caloric content. While the participants were rating the foods, there was increased activity in the insular cortex - a part of the brain that is involved in processing the sensory properties of food.

"Our study sought to determine how people's awareness of caloric content influenced the brain areas known to be implicated in evaluating food options. We found that brain activity tracked the true caloric content of foods," said Dagher. 

The team believe that understanding the reasons behind people's food choices could assist in preventing factors that lead to obesity, and other diet related health problems such as heart disease, and type 2 diabetes.

Source: Association for Psychological Science