London: 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, a new study has found.
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 people to rate 50 common snacks 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".
During this swap-choice task, participants were placed in a functional magnetic resonance imaging (fMRI) scanner, which indirectly measures activity in the brain.
Neither choice behaviour nor accompanying brain activity differed measurably according to participants' body weight.
For both groups, taste was a much better guide to whether a person might choose to swap a food than healthiness.
Following the scanner experiment, participants were presented with an all-you-can-eat buffet with a selection of sandwiches, desserts, drinks and snacks.
For each type of food, there were healthier and less healthy options, such as chicken sandwich and a BLT (bacon, lettuce and tomato) sandwich, or cola and diet cola.
Once they had rated the buffet choices for healthiness and tastiness, the participants were allowed to eat freely and as much as they wanted.
Brain activity predicted the proportion of healthy food consumed in both lean and overweight individuals and both groups selected a greater proportion of foods that they had rated as tasty.
However, the overweight participants consumed comparably more unhealthy foods than lean participants.
The researchers also measured each person's impulsivity or self-control using computer tasks and a questionnaire.
While the level of impulsivity made no difference in lean individuals' selections, the researchers found an association in overweight people between impulsivity and consumption of unhealthy foods - the greater their level of impulsivity, the greater the proportion of unhealthy food they ate.
This effect was apparent only when there was real food available and was not seen during the more hypothetical valuation decisions.
"There's a clear difference between hypothetical food choices that overweight people make and the food they actually eat," said Nenad Medic from University of Cambridge.
"Even though they know that some foods are less healthy than others and say they wouldn't necessarily choose them, when they are faced with the foods, it's a different matter," Medic said.
The study was published in the journal eNeuro.
