0323 GMT October 14, 2019
"What we found is that in humans, the control of body weight is dependent largely on the areas of the brain involved in self-control and self-regulation," said Alain Dagher (@alain_dagher), of the Montreal Neurological Institute and Hospital in Canada. "That area of the brain has the ability to take into account long-term information, such as the desire to be healthy, in order to control immediate desires."
Two hormones, leptin and ghrelin, are known to trigger the body to eat in a weight-loss setting. Previous research confirms that these hormone levels change rapidly when weight is shed. "Everybody who loses weight sees this change in leptin and ghrelin," said Dagher. "It is just that some people, for reasons we do not know, are able to maintain their self-regulation in the face of that signal."
To assess the roles these hormones and self-control have in achieving weight loss, the researchers studied 24 subjects from a weight-loss clinic. Prior to starting a standard 1,200 kcal/day weight-loss diet, all participants received a functional MRI study (fMRI) of the brain, which assessed regions including the lateral prefrontal cortex, which is linked with self-regulation, and the ventral medial prefrontal cortex, a brain area involved in motivation, desire, and value.
Subjects were shown pictures of appetizing foods as well as control pictures of scenery. The researchers compared the brain activity response to the food pictures, particularly the high-calorie food pictures, for each subject at baseline, one month, and three months. "When we show pictures of appetizing foods, the ventral medial prefrontal cortex area becomes more active on fMRI," Dagher said.
During the study, researchers noted that at one month and three months, the signal from the ventral prefrontal cortex went down, and it declined the most in people who were more successful at losing weight. Additionally, the lateral prefrontal cortex signal involved in self-control increased throughout the study.
"In the fMRI, the self-control area increased its activity and the value area decreased its activity," said Dagher. "And the amount of change was predictive of successful weight loss." While all participants lost weight, those who achieved the greatest weight loss had fMRI levels indicating a better ability to self-control. And, at the end of the three-month study, the hormones ghrelin and leptin were starting to return to baseline, suggesting that a new set point was achieved.
"These results suggest that weight loss treatments that increase self-control, such as cognitive behavioral therapy, may be helpful, particularly when stress is involved in leading to overeating," he said. "Stress disrupts the lateral prefrontal cortex control mechanism, but you may be able train people to seek a different strategy."