WASHINGTON — As if the nation’s weight problems were not daunting enough, a new study has found that the body-mass index, the 200-year-old formula used to distinguish between healthy and unhealthy weight, may be misclassifying roughly half of women and just over 20 percent of men as healthy when their body-fat composition suggests they are obese.
The study, published Monday in the journal PLoS One, uses a patient’s ratio of fat-to-lean muscle mass as the “gold standard” for detecting obesity and suggests it may be a bellwether of an individual’s risk for health problems.
The study finds that for women older than 50 especially, many whose BMIs suggest they are the picture of health are, in fact, dangerously fat. The measure in the study uses a costly diagnostic test called dual-energy X-ray absorptiometry, or DEXA, which already is in wide use as a means of evaluating bone density. To recalculate their subjects’ level of obesity, the authors then applied fat-composition standards used by the American Society for Bariatric Physicians.
The research also suggests that BMI is a poor measure of fatness in men, but not always in a way that underestimates their obesity. Far more frequently than for women, men who were obese by the BMI standard were re-categorized as normal and healthy when the DEXA standard was used.
