Overweight people make unhealthier food choices than lean people when presented with real food, even though both make similar selections when presented with hypothetical choices, according to research led by the University of Cambridge and published in the journal eNeuro.
The researchers found that when making hypothetical food choices, lean and overweight people showed highly comparable patterns both in terms of their choices and the accompanying brain activity. The activity in the brain was a good predictor of which foods they would choose when later faced with a selection of real food choices. But the presence of real food influenced choices differently across the groups.
In a related study published recently in the International Journal of Obesity, the researchers show that the brain structure in obese people differs from that in lean individuals in key regions of the brain involved in processing value judgements.
More than 1.3 billion people across the world are overweight and an additional 600 million are obese. Being overweight or obese are leading risk factors for deaths globally, being associated with increased incidence of type 2 diabetes, cardiovascular disease and some cancers.
Previous studies have suggested that obesity is associated with a greater consumption of unhealthy foods – those with high sugar and/or fat content – even though lean and overweight people do not appear to differ in their judgements of the relative healthiness of foods. To help explore further this apparent contradiction, researchers from the University of Cambridge and the Medical Research Council Human Nutrition Unit examined the relationship between how people judge the healthiness and tastiness of food and whether this predicts their food choices at a buffet lunch.
The researchers asked 23 lean and 40 overweight individuals to rate 50 common snack foods, presented on a computer screen, on a five-point scale for their healthiness and tastiness independently. They then examined the degree to which each of these individually-rated attributes appeared to influence a person’s willingness to swap a particular food for one that had previously been rated as “neutral”.
Participants were shown a picture of the “neutral” reference food item at the beginning of the task and told that on each trial they would have to choose between the food item shown on that trial and the reference food item. For example, if they had chosen a granola bar as neutral (and hence their reference food), they might be shown an apple and asked if they would be willing to swap the granola bar for the apple. During this swap-choice task, participants were placed in a functional magnetic resonance imaging (fMRI) scanner, which indirectly measures activity in the brain.