Four days of a moderate dose of caffeine does not alter raw bioelectrical impedance analysis parameters in healthy males

This study investigated the effects of a moderate caffeine dose on resistance (R), reactance (Xc), impedance (Z), capacitance (Cap), and phase angle (PhA) over four days in males. Thirty men aged 20-39 years, with low caffeine consumption (<100 mg/day), participated in this double-blind, randomized crossover trial (ClinicalTrials.gov: NCT01477294). The study consisted of two conditions - caffeine (5 mg/kg/day) and placebo (maltodextrin) - each lasting four days, separated by a three-day washout period.

Assessments were performed at baseline and on the fourth day of each condition. The R, Xc, Z, and PhA were measured through bioelectrical impedance spectroscopy using a frequency of 50 kHz. These were mathematically transformed in a parallel array. Fat mass (FM) and fat-free mass (FFM) were assessed by dual-energy X-ray absorptiometry, while urine specific gravity (USG) was determined using a refractometer. Water intake (WI) was estimated through dietary food records.

A linear mixed model analysis, adjusting for FFM and WI and baseline values, found no significant differences in R, Xc, and Z in both series and parallel arrays, Cap, and PhA across conditions. Comparisons between baseline, placebo, and caffeine conditions did not reach statistical significance for any parameter (p > 0.05). USG values remained stable, indicating no changes in hydration status (p > 0.05).

This study shows that caffeine intake does not significantly affect raw bioelectrical impedance parameters. These findings simplify research by removing caffeine restrictions, enhancing study feasibility, and improving participant adherence. Clinical and sports settings allow for more flexible assessments.