Advancing body composition analysis: Transitioning beyond conventional BMI standards

Background: Body mass index (BMI) remains the primary tool for obesity classification despite its limitations in assessing body composition. This study aimed to evaluate the relationship between different body composition parameters and compare World Health Organization (WHO) and National Health and Nutrition Examination Survey (NHANES) classification systems. Methods: In this cross-sectional study of 3,255 patients (74.3% women) from a Colombian obesity and metabolism center, we analyzed body composition using bioelectrical impedance analysis. We assessed the concordance between the World Health Organization and the National Health and Nutrition Examination Survey classifications, and examined correlations between body composition parameters, with particular focus on phase angle (PhA) as a predictor of muscle mass. Results: While body mass index showed a strong correlation with body fat mass (? = 0.929, p < 0.001), it poorly predicted muscle mass. The World Health Organization and the National Health and Nutrition Examination Survey classifications showed fair overall agreement (? = 0.39), with better concordance in women (? = 0.43) than men (? = 0.28). Multiple regression analyses revealed PhA as a strong predictor of muscle mass (? = 1.032, p < 0.0001, R² = 0.332) but not fat mass (p = 0.525, R² = 0.055). Conclusions: While body mass index adequately predicts adiposity, it falls short in assessing muscle mass. Phase angle emerges as a promising predictor of muscle mass, independent of age and sex, suggesting its potential utility in clinical assessment of body composition.