A picture may worth a thousand calories

Led by Kathleen Page of the University of Southern California, Los Angeles, USA, the research team used functional magnetic resonance imaging (fMRI) to assess the brain responses of 13 obese people – finding that simply viewing images of high calorie foods such as ice cream and cupcakes activated brain regions that control appetite and reward, unlike pictures of non-foods.

"This stimulation of the brain's reward areas may contribute to overeating and obesity," said Page. "We thought this was a striking finding, because the current environment is inundated with advertisements showing images of high-calorie foods.".

Page added that viewing pictures of high-calorie foods also significantly increased ratings of hunger and desire for sweet and savoury foods, whilst ratings of hunger and desire for savoury foods were also higher after ingestion a sugar drink.

"These findings suggest that added sweeteners could be one of the main contributors to the obesity epidemic,” said Page.

Study details

In the study each participant had two fMRI scans as they viewed blocks of images of high-calorie foods as well as low-calorie foods, such as fruits and vegetables, and non-food items. After each block of similar images, participants rated, on a scale of 1 to 10, their hunger and their desire for either sweet or savoury foods.

Halfway through the scans, participants drank 50 grams of glucose on one occasion and an equivalent amount of fructose on another occasion.

The researchers then identified which brain regions activated in response to viewing the images and how sugar consumption influenced brain activation and ratings of hunger and appetite.

In addition to high calorie foods leading to greater brain activation it was revealed that glucose ingestion, compared to fructose, tended to produce greater activation of brain regions involved in reward and motivation for food.