Body Mass Index Underestimates Obesity Levels

Recently, body mass index (BMI), which has been widely considered an effective measure of body fat, has come under scrutiny. According to researchers from Weill-Cornell Medical College in New York, the data produced from BMI measures may grossly underestimate a person’s true fat mass.

The study, published in PloS One (2012; 7 [4], e33308), focused on dual-energy X-ray absorptiometry (DXA) scans
to determine measures of muscle mass, bone density and fat mass in 9,088 individuals. Researchers classified 64% of those individuals as obese. However, BMI measurements indicated that only 26% were obese. Subjects’ average age was 51.

The scientists determined that to maintain accuracy, a specific BMI cutoff point of 28 for adult males and 24 for adult females should be adhered to when BMI is the sole measure being used. “These new cut-points [increase] diagnostic sensitivity with small losses in specificity,” the authors confirmed.

“Our results demonstrate the prevalence of false-negative BMIs, increased misclassifications in women of advancing age, and the reliability of gender-specific revised BMI cutoffs,” the authors concluded. “BMI underestimates obesity prevalence, especially in women with high leptin levels (>30 nanograms
per milliliter). Clinicians can use leptin-revised levels to enhance the accuracy of BMI estimates of percentage body fat when
DXA is unavailable.”