Beyond body mass index: associations between phase angle, vector-derived bioelectrical markers, and selected hematological and physiological alterations in anorexia nervosa

Abstract Purpose Body mass index (BMI) is central to the assessment of severity in anorexia nervosa (AN), but it may not fully capture hematological, biochemical, and hemodynamic abnormalities. This study examined whether phase angle (PA) and bioelectrical vector-derived parameters provide information on these clinical alterations beyond BMI. Methods Fifty-five females with AN were assessed at admission to specialized treatment. Bioelectrical impedance parameters included PA, height-adjusted resistance (Rz/H), and height-adjusted reactance (Xc/H). Clinical indicators included hemoglobin, hematocrit, alanine aminotransferase, urea, blood pressure, and heart rate. Associations were examined using correlations, group comparisons, and regression models adjusted for age, BMI, and recruitment center. Follow-up bioelectrical data were available for 35 patients. Results Lower PA was associated with lower hemoglobin, lower hematocrit, lower systolic and diastolic blood pressure, and higher alanine aminotransferase. PA explained additional variance beyond BMI in hemoglobin, hematocrit, alanine aminotransferase, systolic blood pressure, and diastolic blood pressure. Vector-derived analyses showed a broadly comparable pattern for Xc/H, whereas Rz/H was not significantly associated with the examined outcomes. Patients with PA below reference values had lower hemoglobin and hematocrit despite similar BMI. Conclusion PA and Xc/H were associated with hematological, biochemical, and hemodynamic abnormalities in AN beyond BMI. Bioelectrical assessment may complement anthropometric indices by providing information on selected physiological alterations not fully reflected by BMI. These findings suggest that BMI alone may underestimate clinically relevant abnormalities in some patients with AN. Level of evidence Level III, cohort analytic study.