The circumference of a man's waist is a better predictor of his risk of developing type 2 diabetes than his body mass index (BMI), which is a weight-to-height ratio, or waist-to-hip ratio alone. This finding, published in the March 2005 issue of the American Journal of Clinical Nutrition, is based on data collected from 27,270 men tracked over 13 years who participated in the Harvard Health Professionals Follow-Up Study.
Men who had larger waists (assessed using waist circumference and waist-hip ratio) or higher overall body fat (indicated by BMI) had a greater risk of developing type 2 diabetes. The researchers grouped the study participants into five groups according to their waist size. Compared to those in the group with the smallest waists (29-34 inches), the other groups (34.3-35.9 inches, 36-37.8 inches, 37.9-39.8 inches, 40-62 inches) were 2, 3, 5 and 12 times more likely to develop diabetes, respectively. Similarly, risk was 2, 3, 4 and 7 times greater when waist-hip ratio was measured in men; and 1, 2, 3 and 8 times greater when BMI was measured.
"Both BMI and waist circumference are useful tools to assess health risk," said the study's lead author, Youfa Wang, PhD, MD, assistant professor with the Center for Human Nutrition at the Johns Hopkins Bloomberg School of Public Health. "But abdominal fat measured by waist circumference can indicate a strong risk for diabetes whether or not a man is considered overweight or obese according to his BMI."
The authors suggest that the currently recommended waist circumference cutoff of 40 inches for men may need to be lowered. "Many of the men who developed type 2 diabetes had measurements lower than the cutoff," explains Wang, "and the risk associated with waist circumference increased at a much lower level." While nearly 80 percent of the men in this cohort who developed type 2 diabetes could be identified using a BMI of 25--the cutoff for overweight--only half (50.5 percent) had a waist circumference greater than or equal to 40 inches--the cutoff recommended by the National Institutes of Health.
Men with waist circumference of 40 inches or greater and who also fell into the obese category with a BMI of 30 or greater were at more than twice the risk to get type 2 diabetes as were those who had a high BMI or a high waist circumference alone. In addition to measuring BMI, the investigators recommend that physicians and researchers measure waist circumference instead of the waist-to-hip ratio because it is a better measure of central obesity for predicting the risk of type 2 diabetes and is subject to fewer measurement errors.
The study authors also urge that more research on this topic be conducted with cohorts that include women and different ethnic and racial groups, since the Health Professionals Follow-Up Study only followed a cohort of largely white, professional men who are likely to be healthier than the average American.