Lose weight to gain brain power? Study says it may work

Obese women improved their brain function after they had weight-loss surgery, according to a new study.
(Mark Lennihan / Associated Press)

Weight-loss surgery can make you thinner. But can it make you smarter too?

It’s a question that scientists have wondered about, since they know the reverse is true. Studies have shown that brain function declines in people who have too many extra pounds. Other research has shown that compared with people who are lean, those who are overweight are 26% more likely to develop some type of dementia and those who are obese are 64% more likely to meet that fate.

So a group of researchers from the University of Sao Paolo in Brazil conducted what they believe is the first study to track brain function in patients before and after they had weight-loss surgery. Their results suggest that the brain does indeed benefit from bariatric surgery, though the effects measured were modest.

The researchers recruited 17 severely obese women who planned to have Roux-en-Y gastric bypass, a procedure that shrinks the stomach to the size of an egg and diverts food past a good portion of the small intestine. Both measures reduce the amount of nutrients and calories the body can absorb from food.

The average body mass index for the 17 women was 50.1. (A woman who is 5 feet tall would have a BMI of 50 if she weighed 255 pounds; a woman who is 5 feet, 6 inches tall would have the same BMI if she weighed 309 pounds, according to this table from the National Heart, Lung and Blood Institute.) Six months after their surgeries, their average BMI had dropped to 37.2 – still high enough to qualify as severely obese, according to the Centers for Disease Control and Prevention.


Before they went under the knife, the women took an IQ test and six additional tests to assess their memory and executive function (such as the Stroop Color Test, the Wisconsin Card Sorting Test and the Rey Complex Figure Test). They also gave blood samples and had PET scans so that researchers could measure the metabolic activity in their brains. They repeated all of the tests six months after surgery.

Another group of 16 women served as controls. Their ages and educational levels were essentially the same as for the obese women, but their BMIs were much lower (22.3, on average). The lean women took all the same tests as the obese women, though they did so only once.

It turned out that women in both groups did equally well on the cognitive tests. But compared with their initial results, the obese women improved on one of the tests – the Trail Making Test – after their surgeries, the researchers found.

The differences in brain scans were more pronounced. Before the surgeries, the obese women’s brains appeared to be working harder than the brains of the lean women. That was especially true in areas of the right hemisphere that become active when people have to compensate for cognitive decline, the researchers wrote. However, after the surgeries, these differences “were no longer noticed,” they added.

The blood tests showed that the surgeries made the women more sensitive to insulin and reduced the levels of proteins associated with damaging inflammation. It also increased the levels of a hormone called GLP-1. Similar hormones have been shown to benefit the brain by reducing inflammation as well as the number of beta-amyloid plaques, a hallmark of Alzheimer’s disease.

Overall, the researchers concluded that being obese increases one’s risk of Alzheimer’s by an amount similar to the effect of having the e4 version of the APOE gene. Although it’s impossible to change your APOE gene, the good news for those who are obese is that they can probably reduce their risk of cognitive decline by losing weight, the researchers wrote.

The study was published Tuesday in the Journal of Clinical Endocrinology and Metabolism.

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