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Measuring the Risk of Diabetes

The question is: How fat do you have to be to put yourself at serious risk of diabetes? And then: What's the best way to measure that?

By Kristi Birch

Today some 18 million Americans suffer from diabetes—twice as many as 25 years ago.

Blame it on the nation's growing obesity epidemic. There's little doubt about obesity's association with a risk for type 2 diabetes, which accounts for 90-95 percent of total diabetes cases.

The question is: How fat do you have to be to put yourself at serious risk? And what's the best way to measure that?

The answer might be as simple as the size of your belt, according to Youfa Wang, MD, PhD, lead author of a study that appeared in the March American Journal of Clinical Nutrition.

The current standard for assessing obesity-related risk is body mass index (BMI), a calculation based on weight and height. But according to Wang, an assistant professor of International Health, "Waist circumference is good enough; actually, it's better."

The study, the Harvard Health Professionals Follow-Up, tracked 27,270 men over 13 years, 884 of whom developed type 2 diabetes, and compared the predictive power of three measurements—waist circumference, BMI, and waist-to-hip ratio.

The findings: While BMI and waist circumference were both strong predictors for the disease, waist circumference "can indicate a strong risk for diabetes whether or not a man is considered overweight or obese according to BMI," says Wang, who began analyzing the data three years ago when he was a visiting scholar at Harvard. (Waist-to-hip ratio came in third as a predictor of the disease.)

Furthermore, Wang and colleagues suggest that the current recommended cutoff for waist circumference—40 inches—may need to be lowered. "At roughly 37 inches, the risk [of developing type 2 diabetes] increased four-fold," says Wang. The study was conducted only on men, but Wang says the findings are likely to be similar for women, with lower cutoffs.

Central obesity, or fat around the waist, is associated with type 2 diabetes. "Those fat cells may send out signals to other organs that affect the sensitivity of insulin, and that will affect insulin resistance," says Wang. Type 2 diabetes begins when the body no longer uses insulin properly. Left untreated, diabetes can cause blindness, kidney damage, and a host of other ailments.

"It is increasingly common to calculate BMI. Waist circumference, I sense, is less commonly performed though it's just as easy," says Lawrence Cheskin, MD, director of the Johns Hopkins Weight Management Center.

Actually, according to Wang, it's easier. While the calculations and multiple measurements involved in calculating BMI leave room for error, you don't have to explain to the public how to use a tape measure.