Use Of BMI To Estimate %fat In Civilian And Active Duty Air Force Men And Women

Abstract

Body Mass Index (BMI) is often suggested as a surrogate for %fat in both men and women. Since the military continues to evaluate body composition as a consideration for service, it would be prudent to evaluate the accuracy of BMI to estimate and %fat in active duty (AD) and civilian (CIV) Air Force personnel. PURPOSE: To evaluate the relationship between BMI and %fat in male and female AD and CIV Air Force personnel. METHODS: AD men (n = 453) and women (n = 225) and CIV men (n = 118) and women (n = 179) were stratified by age (18-29 yrs, n = 354; 30-39 yrs, n = 351; >40 yrs, n = 270). Each participant volunteered to be measured by whole body plethysmography to assess %fat. RESULTS: A sex x age x duty (2 x 3 x 2) MANOVA revealed women (34.4 ± 8.5%) were significantly higher in %fat than men (25.7 ± 8.7%), the >40 yr group (31.3 ± 9.0%) was significantly higher than the 30-39 yr group (30.0 ± 9.3%) and 18-29 yr group (27.0 ± 10.0%), but there was no significant difference between AD (28.0 ± 9.1%) and CIV (32.0 ± 10.2%) groups. Correlation between weight and %fat was significantly higher in women (r = 0.74) than in men (r = 0.59) and higher for CIV (r = 0.38) than for AD (r = 0.24). BMI was significantly correlated with %fat in men (r = 0.71) and women (r = 0.81). Regression analysis selected BMI, sex, and age as primary variables in a randomly selected validation group to predicted %fat (R = 0.81, SEE = 5.6%, CV = 19.2%). Cross-validation of the equation on a randomly selected group (n = 204) revealed no significant differences (p = 0.81) between predicted %fat (30.2 ± 8.2% and actual %fat (30.1 ± 8.4%) with a significant correlation between them (r = 0.82, p<0.001). The equation was equally affected for both sexes and service groups. CONCLUSION: %fat can be predicted in Air Force personnel using a BMI equation combined with sex and age with acceptable accuracy. This allows a quick and convenient screening for body composition in both sexes and AD and CIV personnel. Further research might focus on the ability of the prediction equation to longitudinally track body composition changes in military personnel.