Changes in raw bioelectrical impedance parameters as markers of body composition in youth: A prospective cohort investigation

OBJECTIVES: Despite cross-sectional evidence supporting raw bioelectrical impedance analysis (BIA) parameters as informative markers of body composition in youth, their role from a longitudinal perspective remains unclear. We examined how 1-y changes in phase angle (PhA) and other raw BIA parameters were associated with changes in body components at multiple levels in children and adolescents. METHODS: In a 1-y prospective cohort investigation, including 562 healthy and on-time matured youth (51.6% females), we assessed raw BIA parameters with a phase-sensitive 50 kHz BIA device and examined body composition through dual-energy X-ray absorptiometry and related models. The association between changes in raw BIA parameters and changes in body composition by sex and peak height velocity (PHV) stage was analyzed using multiple linear regression. RESULTS: PhA was positively associated with changes in fat-related components, fat-free mass, extracellular water, fluids and solids, osseous minerals, and muscle tissue in females (β = 0.088-0.150; P ≤ 0.05) and with alterations in most body components in males (β = 0.098-0.300; P ≤ 0.05). Similar trends to those of males were observed in both sexes during post-PHV (females: β = 0.149-0.297; males: β = 0.185-0.352; P ≤ 0.05). Other series and parallel BIA parameters exhibited even higher explanatory power of body composition than PhA, with the magnitude of the associations depending on each raw BIA parameter, sex, and PHV stage (females: β =|0.099|-|0.429|; males: β = |0.106|-|0.706|; P ≤ 0.05). Among all raw BIA parameters, the highest associations were observed in resistance adjusted to stature (RI) (total sample and pre-PHV), parallel capacitive reactance adjusted to stature (XcpI), and capacitance (Cap) (both post-PHV). CONCLUSION: PhA emerged as a modest marker of body composition dynamics in youth, particularly in males and during adolescence (post-PHV), whereas other raw BIA parameters, particularly RI, XcpI, and Cap, showed even greater promise in both sexes and across development stages.