WSJ “Numbers Guy” Questions Usefulness of BMI
Wall Street Journal columnist Carl Bialik recently authored two related articles questioning whether body mass index (BMI) is a reliable data point insofar as it “lumps together all body mass, including bone, muscle and beneficial fat, rather than singling out the more dangerous abdominal fat, which most researchers see as the real threat to health.” In particular, Bialik focuses on a recent U.S. Centers for Disease Control and Prevention (CDC) report finding that out of 2.9 million people involved in 97 studies, those participants whose BMI classified them as overweight had a 6 percent lower risk of death than those classified as normal weight.
But Bialik notes that several scientists have since criticized the results of CDC’s report, partly because threshold BMIs in the mid-to-high 20s tend to paint “a wide range of body types… with the same brush.” He adds that Pennington Biomedical Research Center Executive Director Steven Heymsfield, who co-authored commentary accompanying the CDC report in JAMA, has also estimated that BMI misclassifies approximately 5 to 10 percent of the U.S. population. “It is reliable as a measure of over-weight but not over-fat,” elaborated Heymsfield in a January 11, 2013, WSJ blog post. “There are both false positives and false negatives, people who are overweight but not over-fat and vice versa.”
Despite these shortcomings, Bialik suspects that studies continue to rely on BMI because the measurements are low-cost and easy to obtain, even though the co-director of the Office of Obesity Research at the National Institute of Diabetes and Digestive and Kidney Diseases has described BMI “as a screening tool, rather than a diagnostic one.” As a result, some researchers like Heymsfield have apparently advocated including waist circumference alongside BMI as a more direct measure of abdominal fat. “You can get a better fix by also including waist circumference measures,” he reportedly said. “They can put you into groups of high and low risk in the overweight range. I think it’s a good second step.” See The Wall Street Journal, January 11 and 12, 2013.
