Thinner isn’t always better in diabetes

Normal-weight people with the condition have higher mortality than those who are overweight, obese

Skinny doesn’t always mean healthy for people with type 2 diabetes. People who are normal weight when diagnosed with the condition may have a higher risk of death than those who are overweight or obese.

While counterintuitive, the findings may suggest that normal-weight people who have type 2 diabetes are more likely to have other illnesses, frail bones or wasting muscles, researchers report in the Aug. 8 Journal of the American Medical Association.

“This study raises a lot more questions than answers,” says epidemiologist Lynne Wagenknecht of Wake Forest Baptist Medical Center in Winston-Salem, N.C. But the authors have done “a really nice job examining every which way, upside down and right side up of what might be going on here,” she says.

Led by epidemiologist Mercedes Carnethon of Northwestern University Feinberg School of Medicine in Chicago, researchers combined data from five long-term studies that tracked different groups of healthy people for an average of 14 years. They recorded the body mass index, or BMI, and waist circumference of the 2,625 participants diagnosed with type 2 diabetes during the study periods. Compared with overweight and obese people who developed diabetes, normal-weight participants were twice as likely to die during the studies’ follow-up periods.

Doctors often base weight classifications (normal, overweight and obese) on BMI, which is calculated from a person’s height and weight. But factors such as fitness level and body fat are important too, says physician and endocrinologist Hermes Florez of the University of Miami, who coauthored an editorial that appears in the same issue.

“My concern is that people may look at this study and say being overweight or obese is OK,” he says. “The reality is that height and weight don’t tell you the whole story.”

In fact, the researchers found that bigger bellies were also linked to higher mortality. A patient classified as normal weight by BMI could still have a tubby midsection. “BMI is not perfect,” Carnethon says. But it’s very easy to measure, and in most cases can provide physicians with a quick first hint about a patient’s health, she says.

The findings should cue physicians to pay closer attention to normal-weight patients who develop diabetes. For these patients, she says, a normal BMI might be “a red flag for other health problems.”

Meghan Rosen is a staff writer who reports on the life sciences for Science News. She earned a Ph.D. in biochemistry and molecular biology with an emphasis in biotechnology from the University of California, Davis, and later graduated from the science communication program at UC Santa Cruz.

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