Brain MRI offers clues to weight regain after surgery vs diet
medwireNews: Divergent changes in brain activity after bariatric surgery versus a very-low-calorie diet may help explain why people are more likely to regain weight after the latter intervention, a study suggests.
“We provide evidence that those who have undergone bariatric surgery experience three complementary changes in appetitive brain processing compared with those who have lost weight through calorie restriction,” say Tricia Tan (Imperial College London, UK) and co-researchers.
The first of these was areas of the brain involved in the reward system being significantly less activated by food cues in people who lost weight due to surgery than in those who lost it following a 4-week 800 calorie/day total meal replacement diet.
The 35 study participants all met UK National Health Service criteria for bariatric surgery and also had prediabetes or type 2 diabetes but were using no more than one oral antidiabetic agent. Sixteen of these people were scheduled to undergo bariatric surgery and the other 19 were age- and sex-matched people who volunteered for the diet group.
Magnetic resonance imaging revealed that reward system responses were significantly increased in the diet group after 4 weeks of the dietary intervention. However, differences versus the surgical group (4 weeks after intervention) were only significant in a subgroup of 14 participants matched for the amount of weight they had lost. Specifically, this was seen in the nucleus accumbens and the putamen.
In line with this, responses to the Dutch Eating Behavior Questionnaire indicated a significantly larger reduction in the reaction to food cues in the surgery versus the diet group.
The second difference between the groups was in brain regions involved in cognitive control. Here, the team identified significantly increased activity in the diet group versus baseline for the posterior cingulate gyrus, inferior frontal gyrus, and middle temporal gyrus, but no change in the surgery group.
“The concept that weight loss might be related to activity in regions implicated in cognitive control seems intuitive to anyone who has tried, and failed, to diet,” the researchers remark in Diabetes Care.
Looking at specific regions of interest for executive control did not reveal any single differences between the groups post-intervention, but across all these regions there was significant deactivation in the surgery group versus the diet group. This was despite both groups reporting increased restraint related to food.
“[I]t may seem counterintuitive that a reduced activity in areas of cognitive control would protect against weight regain,” say Tan et al.
“However, our data suggest that there is a reduction in requirement for cognitive control after [bariatric surgery], which may be driven by the reduction in reward appeal to food cues and an improved connectivity with the homeostatic system.”
This improved connectivity in areas of the brain involved in homeostatic regulation of bodyweight was the third change the researchers identified. They explain that this regulatory system “is centered on the hypothalamus, which is able to assimilate hormonal cues from adipose tissue and the gut to modulate appetite.”
The team found that, after the interventions, the degree of activation in this brain region in response to food cues was significantly less in the surgery group than the diet group. But they also found increased resting-state connectivity between the hypothalamus and areas involved in the reward system, indicating that the homeostatic system was overall “better engaged” after weight loss caused by surgery than by diet.
Together, these “findings suggest that [bariatric surgery] induces multiple brain activation patterns that may guard against weight regain, whereas [a very-low-calorie diet] induces changes that may make continued weight loss more difficult to sustain,” the researchers conclude.
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