The brain reacts differently to images of food depending on what method people choose for weight loss, according to MRI images.
Researchers used functional magnetic resonance imaging (fMRI) to measure the brain responses of individuals who lost weight after having bariatric surgery and individuals who lost weight by more traditional measures.
When shown images of pizza and other appetizing food, the brains of people who lost weight without surgery were more active in the medial prefontal cortex— the part of the brain known to regulate emotion and evaluate how we feel.
The findings suggest that food means more to people who lose weight by changing their behavior— calorie watching, regular exercise— than it does to people who people who undergo laparoscopic banding surgery. Researchers say the surgery patients appear to be more “disconnected” from the experience of hunger.
Lead author Amanda Bruce, a psychologist with appointments at the University of Missouri–Kansas City and the University of Kansas School of Medicine, says:
“They’re not as interested in eating. They’re not as motivated by food.”
The study is the first to look at brain changes associated with different methods of weight loss.
Food Image Triggers
The scans recorded the study participants’ brain activation levels as they looked at pictures of food. The participants were tested before and after they lost weight.
The 16 diet participants and 15 surgery participants in the study were similar in age, education levels and, most important, body mass indices.
“A huge strength of this paper is that the people in the two different groups were matched on the weight that they lost,” Bruce says.
The bariatric participants had lost about 9.3 percent of their body weight. The dieters had shed 10.8 percent, which was not significantly different.
Bruce says she expected to see differences in the brain activation changes between the two groups. The dieters, she thought, would show increased activity in regions of the brain associated with impulse control or self-regulation.
Value and Motivation
There were differences— but not in the region of the brain Bruce expected.
“The brain area that showed greater change in activation for the diet participants is an area that is associated with attentional processing, salience, how much you value something,” Bruce says.
In hindsight, Bruce says, it makes sense that the dieters had more activity in areas of the brain known to be relate to motivation and the experience of hunger.
“When people are working hard to lose weight, they’re still really focused in on food stimuli,” she says. “They’re thinking about food a lot. That’s one of the challenges. They’re often thinking about the foods they maybe shouldn’t eat. They’re still very motivated by these food stimuli. They’re focused on them.”
Weight Loss Challenges
The bariatric participants were not as focused on food. Their post-weight loss scans showed decreased activation in medial prefrontal cortex, which, the study notes,
“supports the notion that surgical weight loss patients undergo a ‘forced’ dietary restriction in avoiding discomfort that renders food cues to be less rewarding and less salient.”
The participants were selected from two larger studies. One examines brain activation changes after bariatric surgery, and the other by Cary Savage, Professor of Psychiatry and Behavioral Sciences, seeks to understand the brain activation patterns that my help predict successful weight loss and weight maintenance.
Savage’s study is based on the idea that people who want to lose weight fight different challenges.
“When someone one comes in for treatment to lose weight, they’re a very diverse group,” he says.
Brain imaging may seem like an expensive way to segment these individuals. But as Savage notes:
“It’s not as expensive as a six months of diet that doesn’t work or bariatric surgery that’s unnecessary.”
Bruce, A. S., Bruce, J. M., Ness, A. R., Lepping, R. J., Malley, S., Hancock, L., Powell, J., Patrician, T. M., Breslin, F. J., Martin, L. E., Donnelly, J. E., Brooks, W. M. and Savage, C. R.
A comparison of functional brain changes associated with surgical versus behavioral weight loss
Obesity, 22: 337–343. doi: 10.1002/oby.20630