Fat weighs heavy on the brain

New study shows obesity interferes with memory, thinking and reasoning

Obese Person
Obesity may lead to problems with memory and learning, but these abilities may improve again with weight loss. RBFried /iStockphoto
Obesity, or being extremely overweight, isn’t problematic only because of the extra pounds. The condition also boosts a person’s risk of cancer, diabetes and heart disease. Now research indicates that obesity also leads to problems with memory, thinking and reasoning. The good news, an international team of scientists reports, is that the damage may be undone through weight loss.

Earlier studies had connected obesity-related diseases to cognitive problems. The word cognitive comes from cognition, which refers to the brain processes involved in gathering, analyzing and using information. In the previous studies, people with heart disease or high blood pressure — diseases strongly tied to obesity — scored lower on memory, thinking and reasoning tests than did people who didn’t weigh as much.

Health experts define obesity using a scale called the body mass index, or BMI. Anybody can figure out his or her own BMI — it’s a math calculation that uses height and weight. To find out your BMI, follow the “Calculate your BMI” link under “Further Reading.” If a person’s BMI is greater than 30, then that person is considered to be obese.

Charting your body mass index
Charting your body mass index. The National Institutes of Health uses the body mass index, or BMI, to define obesity. People of a healthy weight, in the leftmost purple section, have a BMI between 18.5 and 24.9. NIH
For the new study, scientists wanted to know if obesity caused the lower scores on cognitive tests. The researchers set up an experiment involving 150 obese volunteers. The new study was led by John Gunstad, a psychologist at Kent State University in Ohio who studies how diseases affect thinking abilities.

Gunstad and his colleagues asked the 150 obese people to take cognitive tests. The scientists then compared the test results with those from healthy people. The researchers found that, in general, the obese study participants’ scores were lower than those of healthy people. On some tests, including memory tests, nearly 1 in 4 scored low enough to be considered learning disabled, or handicapped.

After the initial test, 109 of the obese participants underwent a type of surgery that helps people lose weight. Twelve weeks after the procedure, the patients had lost about 50 pounds each. Gunstad and his colleagues tested the group again and found that patients who had lost weight scored higher on memory tests.

That wasn’t true for people who hadn’t lost weight, either through surgery or other ways. Those people did worse on the second round of tests.

“That was a bit surprising,” Gunstad told Science News.

Obesity in Mind
Obesity in Mind. Bundles of nerve fibers in the brain are protected by a white, insulating material. New studies show obesity can damage this material, perhaps making it harder for signals to get from one place to another in the brain. NIH.
In another study, the researchers investigated a possible cause for the connection between obesity and brain functions. The scientists used a tool called magnetic resonance imaging, or MRI, to see inside people’s brains. MRIs, which use magnetic fields and radio waves, produce three-dimensional images of internal organs.

Gunstad and his colleagues used MRI to study the nerve bundles that shuttle information through the brain. A white, fatty substance surrounds and protects these bundles. Gunstad and his colleagues found damage in this protective outer coating in obese people.

“It’s not as though a cable has been cut,” Gunstad told Science News, but the damage could be a problem for signals trying to get from one place to another in the brain.

Mark Bastin, a brain-imaging expert at the University of Edinburgh Western General Hospital in the United Kingdom, told Science News that Gunstad’s MRI work was interesting and thorough. But he noted that because Gunstad’s study was small, the results should be considered an early step in the larger scientific investigation.

Inside the brain, obesity may damage nerve channels. In the bigger picture, obesity impairs thinking, memory and reasoning. In the biggest picture of all, inside and out, obesity is bad news for a person’s mind and matter. About 1 in 3 adult Americans, or 72 million people in this country, are obese, and all face higher risks of heart problems, cancer and diabetes, as well as cognitive problems.

“Doctors have known for a long time that being overweight is bad for your body,” Gunstad says. “It can damage your heart and make it harder to breathe.” Now his research shows that being overweight can also damage the brain, “especially,” he notes, “the parts of your brain most important for paying attention and learning new things. This could make it hard to do your best and get good grades in school.”

In recent years, the number of children and teens who are overweight has been climbing dramatically.   “If this pattern continues,” Gunstad says, “it will put many people at risk for brain damage and problems at school and work.” That’s why he recommends that kids help protect their brain by maintaining a healthy weight, talking to parents and teachers about eating healthy foods, and getting enough exercise. After all, the science argues, “a healthy body leads to a healthy brain.”

Stephen Ornes lives in Nashville, Tenn., and his family has two rabbits, six chickens and a cat. He has written for Science News for Students since 2008 on topics including lightning, feral pigs, big bubbles and space junk.

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