Evaluation of anthropometric equations to assess body-composition changes in young women

Background: Healthy young women who engage in an exercise program may lose fat that is not reflected in body weight changes because of concurrent gain s in fat-free mass (FFM). Objective: This study addressed the question of how well anthropometry-base d predictive equations can resolve these changes. Design: Several widely used skinfold-thickness- or circumference-based equa tions were compared by using dual-energy X-ray absorptiometry to study 150 healthy young women before and after 8 wk of Army basic combat training (av erage energy expenditure: 11.7 MJ/d). Results: Women lost 1.2 +/- 2.6 kg fat ((x) over bar +/- SD) and gained 2.5 +/- 1.5 kg FFM. Fat loss (r = 0.47), but not FFM gain (r = 0.01), correlat ed with initial fatness. Thus, for many women who lost fat, body weight did not change or increased. Fat loss was associated with a reduction in abdom inal circumference but this alone was not a consistent marker of fat loss. One circumference equation and one skinfold-thickness equation yielded the smallest residual SDs (2.0% and 1.9% body fat, respectively) compared with the other equations in predicting body fat. The sensitivity and specificity of the best equations in predicting changes in percentage body fat were no t better than 55% and 66%, respectively. Conclusions: These data suggest that for women, anthropometry can provide b etter estimates of fatness than body mass index but it is still relatively insensitive to short-term alterations in body composition. Not surprisingly , the circumference equation that includes the most labile sites of female fat deposition (ie, waist and hips instead of upper arm or thigh) proved to be the most reliable.