Prediction of phase angle based on body composition: Insights from a large population-based registry

Phase angle (PhA) is obtained through bioelectrical impedance analysis (BIA) and is a potential marker of nutritional health and cellular function. We aimed to develop an equation for estimating PhA using body composition parameters, focusing on skeletal muscle mass, body water, and fat mass.

This cross-sectional study enrolled participants from the Iranian National Obesity Registry. Data on age, gender, body composition, and BIA measurements were collected using an InBody 770 device. Exclusion criteria included pregnancy, pacemakers, implants, or edema. The study was approved by the Ethics Committee of Mashhad University of Medical Sciences.

A total of 5980 participants (28.7% men, 71.3% women) were included. PhA showed the strongest correlations with extracellular water/total body water (ECW/TBW) (r = -0.84, P < 0.001), followed by intracellular water (ICW) (r = 0.62, P < 0.001) and skeletal muscle mass (SMM) (r = 0.62, P < 0.001). Linear regression models revealed a significant negative association between ECW/TBW and PhA (β = -82.81, P < 0.001), explaining 71% of variance. Adding age (β = 0.012, P < 0.001) improved the model (R² = 0.75), and SMM (β = 0.039, P < 0.001) further increased explanatory power (R² = 0.85). Including body fat mass (BFM) (β = 0.005, P < 0.001) and height (β = -0.031, P < 0.001) led to the highest model fit (R² = 0.90).

ECW/TBW, SMM, BFM, age, and height are significant predictors of PhA, with ECW/TBW showing the strongest negative association.