Abstract:
Bioelectrical impedance analysis (BIA) is a practical alternative to dual-energy X-ray
absorptiometry (DXA) for determining body composition in children. Currently, there are
no population specific equations available for predicting fat-free mass (FFM) in South African
populations. We determined agreement between fat-free mass measured by DXA (FFMDXA) and FFM
calculated from published multi-frequency bioelectrical impedance prediction equations (FFMBIA);
and developed a new equation for predicting FFM for preadolescent black South African children.
Cross-sectional data on a convenience sample of 84 children (mean age 8.5 ± 1.4 years; 44 {52%} girls)
included body composition assessed using Dual X-ray Absorptiometry (FFMDXA) and impedance
values obtained from the Seca mBCA 514 Medical Body Composition analyzer used to calculate FFM
using 17 published prediction equations (FFMBIA). Only two equations yielded FFM estimates that
were similar to the DXA readings (p > 0.05). According to the Bland–Altman analysis, the mean
differences in FFM (kg) were 0.15 (LOA: −2.68; 2.37) and 0.01 (LOA: −2.68; 2.66). Our new prediction
equation, FFM = 105.20 + 0.807 × Sex + 0.174 × Weight + 0.01 × Reactance + 15.71 × log(RI), yielded
an adjusted R2 = 0.9544. No statistical shrinkage was observed during cross-validation. A new
equation enables the BIA-based prediction of FFM in the assessment of preadolescent black South
African children.
