I was going to have celery but my brain wanted chocolate!

Choosing healthy snacks instead of junk food might be more difficult than we realised. Scientists have found that, as we read a menu or scan the shelves at the supermarket, our brains are making decisions based on a food’s calorie content.

In a study published in Psychological Science, brain scans were conducted of healthy participants who were asked to examine pictures of various foods. Participants rated which foods they would like to consume and were asked to estimate the calorie content of each food. While they were poor at accurately judging the number of calories in the various foods, their choices and their willingness to pay still centred on those foods with higher calorie content.

“Earlier studies found that children and adults tend to choose high-calorie food,” says Dr Alain Dagher, neurologist at the Montreal Neurological Institute and Hospital and lead author of the study. “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. 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.”

Decisions about food consumption and calorie density are linked to a part of the brain called the ventromedial prefrontal cortex, an area that encodes the value of stimuli and predicts immediate consumption.

It is hoped that understanding the reasons for people’s food choices could help to control the factors that lead to obesity.