Fat-Free Mass Predictions From Anthropometrics in South African Prepubertal Children

South African children face a double burden of malnutrition from undernutrition and rising obesity. Simple, accurate methods to estimate fat-free mass, a key health indicator, are needed, as bioelectrical impedance analysis is limited by cost, availability and lack of local validation.

To develop and validate prediction equations for fat-free mass using simple anthropometric measurements in children aged 6-9 years.

In this cross-sectional study, anthropometric and bioelectrical impedance data were obtained from 117 children. Bioelectrical impedance-derived fat-free mass was used as reference in multivariable regression models. Four equations were externally validated in 75 Black prepubertal children, using dual-energy X-ray absorptiometry-derived fat-free mass as standard. Relationships, mean differences, and agreement were assessed using Pearson's correlation, independent t-tests and Bland-Altman plots, respectively.

Fourteen prediction equations, containing five to nine variables, were developed (R ² range: 0.88-0.92) in the sample of children (51% Black; 55% boys; 7.9 ± 0.8 years). Four equations were strongly correlated with dual-energy X-ray absorptiometry-derived fat-free mass (r > 0.95; p < 0.001) in the validation sample (8.5 ± 1.3 years), and three yielded estimates with acceptable agreement (mean difference: 0.16-0.94 kg; limit of agreement: ±5 kg).

Fat-free mass of prepubertal children can be predicted using simple anthropometric measurements, allowing assessment of body composition in low-resource settings.