Raw bioelectrical impedance parameters as informative markers of body composition in youth

Raw bioelectrical impedance analysis (BIA) parameters, particularly phase angle (PhA), are essential clinical and performance markers. However, their potential as body composition markers remains underexplored in youth. This investigation examined the associations between PhA and other series- and parallel-transformed raw BIA parameters and multiple body components organized at the molecular, cellular, and tissue levels in youth.

A cross-sectional sample of 681 youth (10-17 years, 49 % females) was assessed using a phase-sensitive BIA device (50 kHz), dual-energy X-ray absorptiometry, and a freezing point depression osmometer. Multiple linear regression examined each raw BIA parameter's unadjusted and adjusted relationships with body components.

PhA was associated with all body components in females (molecular level: β = |0.170| to |0.584|; cellular level: β = 0.409 to 0.582; tissue level: β = 0.170 to 0.569) and males (molecular level: β = |0.542| to |0.729|; cellular level: β = 0.612 to 0.729; tissue level: β = 0.714; p ≤ 0.05), independently of relevant confounders. No relationship was found between PhA and fat mass and adipose tissue in males (p > 0.05). Other raw BIA parameters were shown to be even more associated with body composition than PhA in females (molecular level: β = |0.172| to |0.827|; cellular level: β = |0.292| to |0.713|; tissue level: β = |0.635| to |0.821|) and males (molecular level: β = |0.555| to |0.926|; cellular level: β = |0.554| to |0.870|; tissue level: β = |0.827| to |0.916|; p ≤ 0.05). In both sexes, the association power of these BIA parameters was lower regarding fat-related parameters (β = non-significant to |0.460|).

PhA was moderately associated with most body components in youth, except for fat-related components in males, independent of confounding variables. Resistance adjusted to stature consistently emerged as the most relevant marker, highlighting its potential to inform about body composition at an early age.