Does body mass index misclassify physically active young men

• The accuracy of age adjusted BMI for passing or failing body fat standards was 83%.
• The correlation between BMI and % body fat as determined by DEXA was 0.86
• An equation was derived to estimate % body fat: % body fat = 1.3974(BMI) − 19.166.
• Soldiers with a BMI of 27.5 < 30 had 10 kg more fat mass than Soldiers with a BMI < 25.
• Soldiers with a BMI of ≥ 30 had 17 kg more fat mass than Soldiers with a BMI < 25.

ObjectiveThe purpose of this analysis was to determine the accuracy of age and gender adjusted BMI as a measure of body fat (BF) in U.S. Army Soldiers.MethodsBMI was calculated through measured height and weight (kg/m2) and body composition was determined by dual energy X-ray absorptiometry (DEXA). Linear regression was used to determine a BF prediction equation and examine the correlation between %BF and BMI. The sensitivity and specificity of BMI compared to %BF as measured by DEXA was calculated.ResultsSoldiers (n = 110) were on average 23 years old, with a BMI of 26.4, and approximately 18% BF. The correlation between BMI and %BF (R = 0.86) was strong (p < 0.01). A sensitivity of 77% and specificity of 100% were calculated when using Army age adjusted BMI thresholds. The overall accuracy in determining if a Soldier met Army BMI standards and were within the maximum allowable BF or exceeded BMI standards and were over the maximum allowable BF was 83%.ConclusionUsing adjusted BMI thresholds in populations where physical fitness and training are requirements of the job provides better accuracy in identifying those who are overweight or obese due to high BF.