Braverman and his co-author, Dr. Nirav Shah, New York State’s Commissioner of Health, studied 1,400 men and women, comparing their BMI measurement to their percentage of body fat, as measured by a dual-energy X-ray absorptiometry (DEXA) scan. While BMI is a simple ratio of a person’s height and weight, the DEXA scan — which is normally used to measure bone density — can distinguish between bone, fat and muscle mass.
Among the study participants, about half of women who were not classified as obese according to their BMI actually were obese when their body fat percentage was taken into account. Among the men, in contrast, about a quarter of obese men had been missed by BMI. Further, a quarter who were categorized as obese by BMI were not considered obese based on their body fat percentage. Overall, about 39% of participants who were classified as overweight by their BMI were actually obese, according to their percent body fat.