Phase Angle in Bioelectrical Impedance: New Perspectives in Health and Body Composition Assessment

The aim of this observational, descriptive, and cross-sectional study was to analyze the relationship between phase angle (PhA), determined by bioelectrical impedance analysis (BIA), and body composition parameters in healthy adult individuals. The study included 265 participants (122 women and 143 men) aged 18-77 years, examined at a nutritional outpatient clinic in Prague between April 2022 and December 2023. Segmental multi-frequency BIA was performed using the Tanita MC-780 MA analyzer with eight electrodes and frequencies of 5 kHz, 50 kHz, and 250 kHz. The mean PhA values were significantly higher in men than in women (6.29° vs. 5.57°; p < 0.001). A strong negative correlation between the extracellular water-to-total body water ratio (ECW/TBW) and PhA was observed in men (r = 0.78; p < 0.001), whereas in women, the correlation was moderate (r = -0.33; p < 0.001). Conversely, a strong positive correlation was observed between PhA and intracellular water (ICW) volume in women (r = 0.71; p < 0.001), while in men this association was weaker (r = 0.17; p < 0.05). The data indicate that PhA is significantly correlated with body fluid distribution and body composition. The key determinants differ by sex-fat mass, particularly visceral fat, plays a predominant role in men, while in women, muscle mass appears to be the dominant factor. PhA thus emerges as a valid, non-invasive marker of body composition, sensitive to changes in internal milieu, with potential clinical applications for assessing nutritional status and the patient's physiological condition. Keywords Bioelectrical impedance analysis " Phase angle " Body composition " Sex characteristics " Body water distribution.