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Brain changes

Diet or surgery alters our perception of food

Bariatric participants were not as focused on food and their post-weight loss scans showed decreased activation in medial PFC

How we lose weight affects how our brains respond to images of food, according to brain imaging research conducted at the University of Kansas School of Medicine.

The study, published in the journal Obesity, examined brain changes associated with different methods of weight loss.

The findings suggest that food means more to people who lose weight by changing their behaviour (calorie watching, regular exercise) than it does to people who people who undergo surgery. The authors of the study say the surgery patients appear to be more "disconnected" from the experience of hunger.

“They’re not as interested in eating,” said lead author Dr Amanda Bruce, a psychologist with appointments at the University of Missouri–Kansas City and the University of Kansas School of Medicine. “They’re not as motivated by food.”

Researchers used functional magnetic resonance imaging (fMRI) to measure the brain responses of individuals who lost weight after having laparoscopic banding surgery and individuals who lost weight through lifestyle interventions. When shown images of pizza and other ‘appetising’ food, the brains of individuals 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.

Amanda Bruce and Cary Savage

The scans were performed at the Hoglund Brain Imaging Center at the University of Kansas Medical Center. Instruments 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, BMIs.  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.

Although the researchers expected to see differences in the brain activation changes between the two groups, the thought the dieters would show increased activity in regions of the brain associated with impulse control or self-regulation. There were differences, but not in the region of the brain expected.

"A huge strength of this paper is that the people in the two different groups were matched on the weight that they lost," said Bruce. “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.”

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 added. “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.”

In comparison, the bariatric participants were not as focused on food and their post-weight loss scans showed decreased activation in (PFC), which the authors write, "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 papers concludes that “Behavioural dieters showed increased responses to food cues in medial PFC - a region associated with valuation and processing of self-referent information - when compared to bariatric patients. Bariatric patients showed increased responses to food cues in brain regions associated with higher level perception - when compared to behavioural dieters. The method of weight loss determines unique changes in brain function.

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