The study – published in the journal JNeurosci – analysed data from three previous experiments on the amount of grey matter in the brains of 91 people.
The participants were placed in an MRI machines where they were instructed to "consider the healthiness" of a particular food, to "consider the taste" of a particular food or to "make decisions naturally." They were then shown images of foods like yogurt or a cookie and tasked with rating how much they wanted to eat it.
The test found that those who thought more about the healthiness of an item or less about its tastiness had more grey matter in two areas of their prefrontal cortices – the dorsolateral prefrontal complex (which plays a role in cognitive skills like memory and attention) and the ventromedial prefrontal cortex (which influences emotional control and decision-making processes).
A second group of people were then put through a slightly different test. Different participants were placed in an MRI machine but were told to "distance" themselves from the food, "indulge" in the food or "make decisions naturally” before being shown the images. They were then asked how much they would splash out on each item, from $0 to $2.50. Again, those with the most self-control had more grey matter.
But that doesn’t mean that willpower is out of your hands. Researchers say that future studies should examine how the brain can be trained to resist unhealthy food.
“Brain is plastic, so your brain structure changes over time," senior study author Hilke Plassmann told Live Science. "I don't want people to say, 'I'm just not good at self-control; I can't change it.”