Development and validation of bioelectrical impedance analysis equations for predicting total body water and fat-free mass in North-African adults.

Abstract

Accuracy of the bioelectrical impedance analysis (BIA) depends on population-specific prediction equations. The aim of our study was to develop prediction equations for assessing total body water (TBW) and fat-free mass (FFM) in healthy North-African adults. In all, 250 participants (194 women, 56 men) aged 18-64 years were included in the analysis. BIA variables were measured by a tetra-polar device. TBW and FFM were assessed by the dilution of deuterium (D2O). The participants were sorted by gender and randomly split into development and validation subgroups. The validity of other published equations was also tested using Bland and Altman procedure, proportional bias and pure error. The prediction equations derived were: TBW (l)=5.68+0.267 height(2)/resistance+4.42 sex (male=1, female=0) + 0.225 weight-0.052 age (R(2)=0.92, root mean square error (RMSE)=1.75 l, RMSE%=5.65); and FFM (kg)=7.47 + 0.366 height(2)/resistance+6.04 sex + 0.306 weight-0.063 age (R(2)=0.92, RMSE=2.38 kg, RMSE%=5.61). The new equations provided nonsignificant proportional bias values, and better agreement than other tested equations. Bias and pure error values were 0.36 and 1.88 l for men and 0.00 and 1.82 l for women, for TBW equation. For FFM equation, bias values were 0.43 and -0.04 kg, and pure errors were 2.57 and 2.46 kg for men and women, respectively. The new prediction equations provide reliable estimates of TBW and FFM in North-African adults and are recommended for use in these populations.