The brains of people who lost weight and kept it off responded differently to images of foods like ice cream compared to normal-weight individuals or those who regained the pounds, according to a new U.S. study. (HO, California Walnuts/Canadian Press)

People who lose weight and keep it off may have different brain activity patterns than those who pack the pounds back on, according to a new U.S. study.

The researchers, whose findings are in the October issue of the American Journal of Clinical Nutrition, monitored blood flow in the brains of people who successfully maintained their weight loss, as well as obese or normal-weight individuals.

"Our findings shed some light on the biological factors that may contribute to weight loss maintenance," said the study's lead author, Jeanne McCaffery, of The Miriam Hospital's Weight Control and Diabetes Research Center in Miami.

"They also provide an intriguing complement to previous behavioural studies that suggest people who have maintained a long-term weight loss monitor their food intake closely and exhibit restraint in their food choices," she added in a release.

On average, people who participate in behavioural weight-loss programs lose eight to 10 per cent of their weight during the first six months and maintain two-thirds of that at the one-year followup, the researchers said.

Inhibition areas

But most regain the pounds after five years, the reason the team is trying to understand the factors that contribute to weight-loss maintenance.

McCaffery and her colleagues used functional MRI, a non-invasive technique that shows patterns of brain activity, to test:

• Eighteen people of normal weight.
• Sixteen obese people.
• Seventeen people who shed weight — at least 30 pounds from their maximum weight — and kept it off for at least three years.

All of the participants fasted for four hours and then had their brains scanned while they looked at three different types of pictures:

• High-calorie foods like cheeseburgers and ice cream.
• Low-calorie foods such as whole grain cereals and salad.
• Non-food items with similar visual complexity, texture and colour, such as rocks and trees.

Scans of subjects in the successful weight-loss group showed strong signals in the left superior frontal region and right middle temporal region of the brain — areas associated with inhibition and greater visual attention to food cues.

"This greater engagement of inhibitory control regions in response to food cues and greater monitoring of foods may mediate control of food intake and successful weight-loss maintenance," the study's authors concluded.

Study subjects of normal weight didn't show the same pattern, perhaps because they don't need to pay such close attention to controlling their impulses.

"The fact these responses differ from obese and normal-weight subjects is interesting," but several questions remain, said Ian McDonald, a professor of metabolic physiology at University of Nottingham Medical School in the U.K., in a commentary accompanying the study.

For example, he asks, did people who kept the weight off begin to show this brain response when they started losing weight or afterwards? If so, do the unhealthy eating habits of heavy people lead to differences in how their brains respond when looking to food?

Similar brain scanning measurements need to made before, during and after weight loss, to help figure that out, he said.