Severe weight gain is controlled to a great degree by your brain, research by a team at the Montreal Neurological Institute suggests.

One of five Quebec adults is obese — a condition defined by having a body mass index (BMI) greater than 30.

Analyzing results of cognitive tests and magnetic resonance imaging conducted on 1,200 overweight people, researchers Uku Vainik and Alain Dagher of the Montreal Neurological Institute found notable differences in the brains of those people studied versus those who maintain what is designated as a normal BMI between 18.5 and 25.

The research found that the right prefrontal cortex is thinner and the left amygdala larger in the brains of those who are overweight, which the study contends favours a more intense reaction to the stimuli provided by food.

According to the study, individuals who are overweight have less cognitive flexibility and a diminished capacity to resist pleasure — such as that provided by eating — than those who maintain a normal weight range.

“Obesity is a result of behaviour, the behaviour being to over-consume calories, and what we’ve found is that (behaviour) comes from the brain,” Dagher said.

The study also examined members of the same family as well as twins, which allowed researchers to note that “these factors in the brain can be inherited.”

“So it probably comes from genetic factors,” Dagher said. “We can inherit this vulnerability to overeating.”

The situation is aggravated by what the study refers to as an “obesogenic” environment that makes extra calories easily available to those who overeat.

However, as is often the case, genetics don’t tell the whole story. And those whose brains seem wired to foster overeating and obesity are not necessarily fated to be overweight.

“Nothing is truly predetermined,” Dagher said. “We’re just talking about influence. We know that 70 to 80 per cent of your weight variability comes from genetics. However, when people do a lot of physical activity, that (influence) drops to 30 per cent.

“That behaviour — physical activity — can eliminate the genetic effect or reduce it greatly.”