If you're middle-aged and your memory's not what it used to be, check the bathroom scale. Excess weight could be sabotaging your brain power, a new study shows.

The study compared mental abilities to body mass index (BMI), a measurement of weight in relation to height used to define overweight and obesity. A BMI of 25 or more indicates overweight, and 30 or more is obese.

Middle-aged adults with a high BMI scored lower on memory and other mental ability tests than did middle-aged adults with a healthier body mass index, says Maxime Cournot, MD, assistant professor of clinical epidemiology at Toulouse University School of Medicine in France.

Cournot is a researcher for the study, published in the Oct. 10, 2006, issue of the journal Neurology.

"Our results can have an additional motivational effect to modify health habits in people who are overweight," Cournot tells WebMD. "Our conclusions stress the need to implement preventive programs to control obesity before cognitive impairment, as minor as it may be, [occurs]."

The study isn't the first to suggest this link, especially in the elderly, but Cournot's study is larger than some previous ones and included much younger adults.

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The French Study

Cournot's team looked at the relationship between BMI and the ability to think, learn, and remember in 2,223 healthy men and women in France who were aged 32 to 62 when the study started in 1996. First, the participants' heights and weights were recorded, and they were divided into five BMI groups, ranging from lowest to highest BMI ranges.

Participants then took a series of tests, including being given a list of 16 words and asked to remember them either immediately or in delayed "free recall," writing down as many words as they could remember from the list. Another test was for selective attention; participants scanned a line of 58 alphabet characters to find a specific letter shown in the margin and cross it out.

Five years later, the entire process was repeated.

Among the word-list learning tests, the delayed recall one was most associated with BMI, Cournot says. Those with in the lowest range of BMI (15-21.5) remembered nine of 16 words, while those in the highest BMI range (27.7-45) could remember just seven. The results were linear -- so as BMI went up, the number of words remembered declined.

Those who had a higher BMI in 1996 tended to have a higher decline in mental abilities in 2001, Cournot says. There was no association between changes in BMI from 1996 to 2001 and functioning, but the participants overall did do better on the second round of tests. Cournot says that might be due to familiarity with the tests.

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The Underlying Link

What's behind the link? "There are two strong hypotheses," Cournot says. Since obesity can lead to heart and blood vessel disease, including hardening of the blood vessels or atherosclerosis, the brain's blood vessels might be affected and not function as well.

Excess weight can also lead to poorer management of the body's insulin, and that could be affecting brain cells as well.

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Other Experts Weigh In

Others familiar with the association say the new study makes sense. "It provides even more support for the ideas that there is a link between excess weight and brain function," says John Gunstad, PhD, an assistant professor of psychology at Kent State University in Kent, Ohio. He gave 486 healthy adults, aged 21 to 82, memory tests and also found that an obese BMI, at any age, reduced memory performance. In his study, published in March 2006 in the journal Eating and Weight Disorders, he found a relationship between obesity and reduced memory performance to be independent of a person's age.

Cournot's study "is consistent with the idea that Alzheimer's disease is the end of a process," says Gary Small, MD, director of the University of California Los Angeles Center on Aging and author of The Memory Bible. "I see a lot of people concerned about their memory," he says. "I always ask them, 'How is your diet?' and 'Do you exercise?'"

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Take-Home Points

Obesity and dementia are both on the rise, and Cournot contends that managing obesity in middle-aged adults might help reduce dementia later.

"Try to find ways to manage your weight," Gunstad says. "We've known [for many years] that obesity is linked to high blood pressure and other problems. The fact that its impact on brain function may be independent [of other problems] is newer."

By Kathleen Doheny, reviewed by Louise Chang, MD

SOURCES: Maxime Cournot, MD, assistant professor of clinical epidemiology, Toulouse University Hospital, France. John Gunstad, PhD, assistant professor of psychology, Kent State University, Kent, Ohio. Gary Small, MD, director, University of California Los Angeles Center on Aging. Neurology, Oct. 10, 2006; vol 67: pp 1208-1214.