Development of bioelectrical impedance-based equations for the prediction of body composition of Malawian adolescents aged 10–18 years: a cross-sectional study

OBJECTIVES: The accuracy of bioelectrical impedance analysis (BIA) depends on population-specific prediction equations and there is no population-specific equation for predicting fat-free mass (FFM) in Malawian adolescents. This study aimed at determining the agreement between FFM measured by deuterium oxide dilution technique (the reference) and FFM by BIA; and propose BIA-based prediction equations to estimate FFM for Malawian adolescents. DESIGN: This was a cross-sectional study. SETTING: The study was conducted in Blantyre, Malawi PARTICIPANTS: 186 Malawian adolescents aged between 10 and 18 years were included in this study. Body composition was estimated by both the BodyStat BIA analyser and the deuterium oxide dilution method. RESULTS: BIA inbuilt equation underestimated FFM compared with deuterium oxide dilution (p=0.039). The new prediction equation for FFM (kg)=−4.316+ 0.425* height(2)(cm)/resistance (Ω)+1.287* sex (male=1, female=0)+0.307*age(years)+0.344* weight(kg)+0.019*reactance(Ω) yielded an R2 of 0.926. The equation for total body water (TBW) (kg)=−2.152 + 0.328*height(2)(cm)/resistance (Ω) 0.910*sex (male=1, female=0)+0.307 *age (years)+0.249*weight(kg)+0.015*reactance(Ω) yielded an R2 of 0.922. The Bland-Altman plot illustrated a good level of concordance between the FFM and TBW predicted by the new equations and the values derived using deuterium dilution method. CONCLUSIONS: The new BIA prediction equations for estimating FFM and TBW could be used to assess with very good accuracy and precision the body composition of Malawian and adolescents with similar characteristics.