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Overweight people tend to choose unhealthier foods to eat compared to lean people, even though both groups seem to make similar choices when given hypothetical situations. Brain activity seems to be a good predictor of which foods finally get chosen.

Being overweight or obese increases a person's morbidity and mortality risk worldwide as they are associated with the development of issues such as cardiovascular diseases, type 2 diabetes and certain cancers.

Research was conducted by the University of Cambridge in the U.K. to look what food choices were made by overweight people and what factors made them decide on such choices. 

It was noted that although overweight and lean people made similar hypothetical food choices when questioned by researchers, it was observed that overweight people made unhealthier choices when picking out real food to consume. It was then discovered that there were structural differences in key areas of the brain involved in processing value judgements in overweight/obese people. 

Findings of the study

Researchers interviewed 40 overweight and 23 lean individuals to rate pictures of 50 commonly available snacks regarding the healthiness and tastiness of the products. The participants were then examined to see whether they had an inclination to replace their choices with a certain product that was marked as being neutral.

A neutral product would be shown to the participants at the beginning of the task. The task then was to compare the neutral product with the given one, and the participant had to decide whether they would replace the neutral product or keep it as is. This was all done while the participants were placed in a functional magnetic resonance imaging (f-MRI) machine and had their brain activity interpreted.

It was found that the willingness to swap a given food was associated with increased activity in the ventromedial prefrontal cortex of the brain; an area which is known to be linked with the degree in which people value rewards. The activity in this area was similar across both groups in the above-mentioned task. In another study it was noted that the grey matter, of the mentioned area of the brain, in people with a higher body mass index seemed to be thinner

Following this test, the participants were invited to enjoy an all-you-can eat-buffet. This spread included healthy and not-so-healthy food choices. The buffet choices were then rated on a scale of healthiness and tastiness, just like in the visual test. 

It was noted that brain activity predicted the proportion of healthy food that would be consumed by people from both groups based on the tastiness of those foods. What was also discovered was that the participants in the overweight group tended to consume more unhealthy foods than their lean counterparts.

Another aspect that was measured in this study was the impulsivity or self-control of the participants. It was noted that individuals in the overweight group seemed to have higher levels of impulsivity which had a direct effect on their unhealthy food choices. This was true when choosing real foods to eat and not so in the visual test.

The clinical significance of this study

Clearly, there's a big difference when overweight people are making hypothetical and real food choices. It would seem then that food choices don't appear to be based on a rational decision, and these findings would suggest that just trying to educate people about the healthiness of food choices is just not enough.

The problem of translating what one decides hypothetically versus what decisions are made in the real world could lie in the structural differences in the brain or overweight people.

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