Where You Carry Your Weight Does Matter

A study of 8,745 women ages 65 to 79 found that those who carried their weight around their hips had tested lower on memory, reasoning and other mental skills than women with big midsections. “Obesity is bad, but its effects are worse depending on where the fat is located,” says lead author Diana Kerwin, M.D., an assistant professor of medicine at Northwestern’s Feinberg School of Medicine.

For every one point over the woman’s normal body mass index, or BMI (a measure of body fat based on height and weight), researchers found a corresponding one point difference in the woman’s cognitive test scores compared to women with lower BMI measures. For example, a woman who was 5-foot-5 and weighed 180 pounds with a BMI of 30—five points higher than normal—scored about five points lower on the mental tests than those with lower BMIs. (Calculate your BMI here.)

The study, published this week in the Journal of the American Geriatric Society, adds to growing research that links aging America’s expanding girth to a shrinking brain.

A study in May by the Boston University School of Medicine found a link between big bellies and decreasing brain volume in older adults. Smaller brains have been linked to a higher risk of dementia. A 2008 study of more than 6,500 people by the Kaiser Permanente Division of Research found that those who had big bellies in their 40s were much more likely to get Alzheimer’s and other forms of dementia in their 70s.

Hip fat, belly fat

The results of the Northwestern study were surprising because it was the women with hip fat, not abdominal fat, who had a greater decline in brain function, says Kerwin.

For many years, doctors have warned that apple-shaped women with protruding bellies had a higher risk of developing diabetes, heart disease, breast cancer and other conditions. That’s because belly fat produces more hormones. Unlike thigh fat, which builds up just below the skin, belly fat is deposited deep into the abdomen, encasing the internal organs, and producing hormones that can cause a variety of problems, including insulin resistance and increased estrogen levels.

For this reason, says Kerwin, “I assumed apples would do worse [in the study] because they had more risk of high blood pressure, stroke and diabetes and that would have an effect on brain function. But I didn’t see that.”

Fat cells produce cytokines, a hormone that can cause inflammation and likely affect cognition, Kerwin says. “We need to find out if one kind of fat is more detrimental than the other, and how it affects brain function,” she says.