(HealthDay News) – The body mass index (BMI) substantially underdiagnoses obesity when compared to the dual-energy X-ray absorptiometry (DXA) scan, a direct simultaneous measure of body fat, muscle mass, and bone density.

Nirav R. Shah, MD, of New York University, and Eric R. Braverman, MD, of Weill-Cornell Medical College – both in New York City, conducted a retrospective chart review of 9,088 patients who had outpatient visits at a multispecialty private practice from 1998–2009. Data were analyzed for 1,393 adults (mean age, 51.4 years) with available data for BMI, DXA, and fasting leptin and insulin levels.

The researchers found that, of the 1,393 participants (63% female and 75% white), mean BMI was 27.3kg/m² (SD=5.9) and mean percent body fat was 31.3% (SD=9.3). BMI characterized 26% of the subjects as obese, while DXA indicated that 64% of them were obese. Thirty-nine percent of the subjects were classified as non-obese by BMI but were found to be obese by DXA. BMI misclassified 25% of the men as obese and 48% of the women as non-obese. A strong relationship was found between increased leptin and increased body fat.

“Our results demonstrate the prevalence of false-negative BMIs, increased misclassifications in women of advancing age, and the reliability of gender-specific revised BMI cut-offs,” the authors write.

The research was funded by the PATH Foundation, which has received financial support from the Life Extension Foundation. The authors disclosed financial ties to the pharmaceutical and medical industries.

Full Text