Validity of Slaughter Equations and Bioelectrical Impedance Against Dual-Energy X-Ray Absorptiometry in Children

Abstract

Objectives: i) To analyze the criterion validity of Slaughter’s equations (Slg-Eq) and bioelectrical impedance analysis (BIA) to estimate body fat percentage (BFP) and fat mass index (FMI) at different degrees of obesity in children, compared to dual-energy X-ray absorptiometry (DXA); and ii) to determine their agreement over the time. Methods: 92 children with overweight/obesity (10.0±1.2 years; 34.8% girls) participated in this 20-week study. Anthropometric, BIA and DXA measurements were performed. Results: i) Both Slg-Eq and BIA methods underestimated BFP and FMI against DXA and the bias was markedly larger with BIA (Mean Absolute Percentage Error-MAPE=11% for Slg-Eq vs. 18-21% for BIA); a larger underestimation was observed in girls compared to boys for Slg-Eq (P≤0.001), and the observed underestimation in adiposity was reduced as weight status increased. ii) Systematic errors were kept constant over the time, so that no large differences between methods were observed in the change in adiposity. Conclusions: At the group level, Slg-Eq provides a more valid estimation of BFP and FMI than BIA. At the individual level, Slg-Eq shows larger estimation errors. The validity of these methods might differ in sex and weight status. Nevertheless, both methods seem to be valid for monitoring changes in adiposity.