Body fatness and bioelectrical impedance in non-obese pre-menarcheal girls: comparison to anthropometry and evaluation of predictive equations

Objectives: To determine in non-obese pre-menarcheal girls if bioelectrical impedance (BIA) is a better predictor of body fatness than triceps skinfold (TSF) or body mass index (BMI) and to cross-validate published equations for determination of fat-free mass (FFM) from BIA in pre-menarcheal girls. Design: Cross-sectional analysis of data from 132 non-obese pre-menarcheal girls. The relationship of percent body fat (%BF), derived from isotopic dilution of (H2O)-O-18 to TSF, BMI, and %BF by BIA, calculated from measures of height, weight and resistance was examined by correlation analysis. Setting: Massachusetts Institute of Technology (MIT) Clinical Research Center in Cambridge, MA, USA. Subjects: Pre-menarcheal girls aged 8-12 y were recruited from local schools, MIT summer day camp and by word of mouth. Results: TSF accounted for 68% of the explained variance (R-2) in the prediction of %BF measured by (H2O)-O-18, compared to 38% for BMI and 70% for BIA. Prediction of FFM by comparison of published equations was evaluated in this population. The predictive ability differed by Tanner stage. Kushner's equation (Kushner et al, 1992), based solely on height(2)/resistance was the only equation that provided estimates that did not differ significantly from measured values among all Tanner stages. Conclusions: BIA appears to be a valid and reliable measure of FFM but is no better than TSF in predictions of body fat.