Body shape may affect mental acuity

Big apples fare better than plump pears

Being fat may diminish mental performance, studies find — a problem that worsens with age. But among elderly women, where fat is deposited may matter. To wit: The big apple is sharper than the obese pear.

Genetics dictates where people preferentially accumulate body fat. For most it’s around the belly. Among the obese, these apple-shaped individuals tend to run a bigger risk of developing heart disease than do pears — people who deposit most of their excess fat at the hips and thighs. For a host of reasons, physicians had expected that if body shape affected mental performance, apples would again prove the bigger losers.

In fact, the opposite appears true, Diana Kerwin of Northwestern University’s Feinberg School of Medicine in Chicago and her colleagues report online July 14  in the Journal of the American Geriatrics Society.

The team pored over data collected from more than 8,700 women, all 65 to 79 years old. These were a healthy subset of incoming participants to the Women’s Health Initiative study. This long-running trial at 40 medical centers across the country has been investigating the role of hormone-replacement therapy and diet on risk of heart disease, fractures and certain cancers.

Each woman was administered a test of memory and reasoning known as the Modified Mini-Mental State Examination, or 3MSE. Kerwin’s team correlated a participant’s score with her shape and her height-adjusted weight — something known as body-mass index, or BMI. BMI values were divided into six categories, with 1 being lean and 6 morbidly obese.

Most women scored within the normal range of 90 to 100 on the 3MSE, Kerwin notes. However, among pear-shaped overweight women, for every increase in BMI category, the 3MSE score dropped by roughly half a point. This held even after adjusting for potentially confounding factors such as age, education and cardiovascular disease risk. How memory and reasoning might have altered over time remains unknown, Kerwin observes, since women took the cognitive test only once, upon entering the study.

Among apples, the fatter they were, the higher their mental-acuity score, although the difference from slim to morbidly obese was only around 2 points out of 100 possible — and the biggest increase occurred between the slim and normal-weight categories.

“Apples were better? That is surprising,” says geriatrician John Morley of the Saint Louis University School of Medicine. “It’s very difficult to explain,” he says, because based on blood levels of triglycerides, or fats, “the higher levels (which you get in the apple, not in the pear) interfere with memory.” On the other hand, he notes, “fat produces leptin [a hormone that plays a role in regulating fat storage]. And we’ve shown that leptin increases memory. It’s really the fat around the stomach that is a leptin producer.”

Kerwin says her data indicate the link between body shape and cognition is complex. For instance, slim to normal-weight, very pear-shaped women had the highest mental-acuity scores and lean apples the lowest. Overall, normal-weight women tended to outperform overweight women of either shape. So, she argues, there’s no advantage in normal-weight women becoming big apples.

Janet Raloff is the Editor, Digital of Science News Explores, a daily online magazine for middle school students. She started at Science News in 1977 as the environment and policy writer, specializing in toxicology. To her never-ending surprise, her daughter became a toxicologist.

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