Brain study reveals why some people fail to stick to their diet

Differences in brain anatomy might explain why some individuals struggle to maintain a healthful diet while others do not.

This was the conclusion that researchers came to after finding that gray matter volume in two brains regions predicted ability to exercise control over food choices.

The brain regions are the dorsolateral prefrontal cortex (dlPFC) and the ventromedial prefrontal cortex (vmPFC). These are believed to be important for evaluating options and self-control.

In a paper now published in the Journal of Neuroscience, the researchers suggest that the findings identify brain markers that might predict "dieting success and failure" and provide possible treatment targets for "obesity and related eating disorders."

The study should also advance research into better ways to assess and treat eating disorders that involve problems with self-control, such as binge eating and anorexia nervosa.

"It is not always very clear," says senior study author Hilke Plassmann, who is the INSEAD Chaired Professor of Decision Neuroscience, based at Fontainebleau in France, "how to assess these disorders."

The 'neuroeconomics' of food

The study belongs to the science of neuroeconomics, which analyzes the "brain functions behind decision-making."

Researchers in this field suggest that there are two mechanisms that govern how we choose the food we eat. First, we evaluate each feature of a food item. One feature, for example, may be "tastiness," while another might be "healthfulness."

We then select the item that has the highest total value after taking into account the importance that we give to each feature.

Prof. Plassmann and her colleagues wanted to investigate what brain structures might be involved in such choices and whether there is anything about them that might predict ability to select healthful ones.

They studied imaging data from brain scans taken of healthy people — 45 men and 78 women — as they made choices about food.

The men and women took part in a series of experiments as they underwent MRI scans of their brains.

Gray matter and dietary self-control

During these experiments, the participants looked at images of food items and were asked to place values on them according to tastiness and healthfulness. They were also asked to make a choice based on healthfulness.

When they compared the imaging data against the choices, the scientists found that volume of gray matter in the dlPFC and the vmPFC was a good predictor of healthful choices.

The findings revealed that people with more gray matter volume tended to show more self-control. They did this by either putting a higher value on healthfulness or a lower value on tastiness when asked to consider healthfulness.

The researchers also found a similar relation between gray matter volume in the vmPFC and dlPFC and "dietary self-control" in another dataset with different subjects and a different kind of task that "entailed distancing from cravings for unhealthy, appetitive foods."

They say that their study is the first to show that differences in dlPFC and the vmPFC anatomy may influence people's choice of healthful foods. However, the findings do not suggest that people have to accept these conditions as fixed.

The brain has "plasticity," which means that it can adapt. Gray matter volume is similar to muscle and can be developed with "exercise."

"In the future, we may be able to come up with brain-based interventions, so that you can change the gray matter density in these regions."

Prof. Hilke Plassmann