Development of a single-frequency bioimpedance prediction equation for fat-free mass in an adult Indigenous Australian population

Background/Objectives: To describe the development of a single-frequency bioimpedance prediction equation for fat-free mass (FFM) suitable for adult Aboriginal and Torres Strait Islander peoples with and without diabetes or indicators of chronic kidney disease (CKD). Subjects/Methods: FFM was measured by whole-body dual-energy X-ray absorptiometry in 147 adult Indigenous Australians. Height, weight, body circumference and resistance were also measured. Adults with and without diabetes and indicators of CKD were examined. A random split sample with internal cross-validation approach was used to predict and subsequently validate FFM using resistance, height, weight, age and gender against measured FFM. Results: Among 147 adults with a median body mass index of 31 kg/m², the final model of FFM was FFM (kg)=0.432 (height, cm²/resistance, ohm)-0.086 (age, years)+0.269 (weight, kg)-6.422 (if female)+16.429. Adjusted R² was 0.94 and the root mean square error was 3.33 kg. The concordance was high (r_c =0.97) between measured and predicted FFM across a wide range of FFM (31-85 kg). Conclusions: In the context of the high burden of diabetes and CKD among adult Indigenous Australians, this new equation for FFM was both accurate and precise and based on easily acquired variables (height, weight, age, gender and resistance) among a heterogeneous adult cohort.