Phase angle reveals blood and heart signs of anorexia nervosa that BMI misses

Body mass index has long been the anchor for judging severity in anorexia nervosa, but a new study suggests it tells only part of the story. Researchers report that phase angle, a measure derived from bioelectrical impedance analysis, was associated with a range of hematological, biochemical, and hemodynamic abnormalities in female patients, and that it explained variation in these clinical indicators beyond what BMI alone could account for.

The study, published in Eating and Weight Disorders – Studies on Anorexia, Bulimia and Obesity, enrolled 55 females with anorexia nervosa who were assessed at admission to specialized treatment. The work is classified as a Level III cohort analytic study, and the article is available as open access. Because the patients were evaluated at a single admission time point, the findings describe associations at that moment rather than effects of any intervention.

The researchers also examined two height-adjusted impedance parameters: resistance divided by height (Rz/H) and reactance divided by height (Xc/H), which together form the basis of vector-derived bioelectrical analysis.

The clinical indicators the team tracked included hemoglobin, hematocrit, alanine aminotransferase, urea, blood pressure, and heart rate.

The results were consistent across several analytical approaches. Lower phase angle was associated with lower hemoglobin, lower hematocrit, lower systolic and diastolic blood pressure, and higher alanine aminotransferase. In regression models adjusted for age, BMI, and recruitment center, phase angle explained additional variance in hemoglobin, hematocrit, alanine aminotransferase, systolic blood pressure, and diastolic blood pressure beyond BMI. The adjustment for BMI is the key detail: it means the bioelectrical marker carried information about these abnormalities that the body mass index itself did not capture.

Vector-derived analyses showed a broadly comparable pattern for Xc/H, the height-adjusted reactance. In contrast, Rz/H, the height-adjusted resistance, was not significantly associated with the examined outcomes.

One of the most striking comparisons involved patients grouped by whether their phase angle fell below reference values. Those with a phase angle below the reference range had lower hemoglobin and lower hematocrit than the other patients, despite having similar BMI. In other words, two patients who would look equivalent on a standard severity assessment could differ in measurable blood parameters, and the bioelectrical marker flagged that difference.

The authors conclude that phase angle and Xc/H were associated with hematological, biochemical, and hemodynamic abnormalities in anorexia nervosa beyond BMI, and that bioelectrical assessment may complement anthropometric indices by providing information on selected physiological alterations not fully reflected by BMI. They note that these findings suggest BMI alone may underestimate clinically relevant abnormalities in some patients with anorexia nervosa.

Several limitations frame how far these conclusions can be extended. The sample consisted of 55 female patients assessed at admission, and follow-up bioelectrical data were available for only 35 of them. The study examined associations using correlations, group comparisons, and adjusted regression models; it did not test whether bioelectrical markers predict clinical outcomes over time or whether monitoring them improves treatment. The examined indicators were also a selected set, and urea and heart rate did not emerge among the associations highlighted in the results.

Subject of Research: Associations between phase angle, bioelectrical vector markers, and hematological and physiological alterations in anorexia nervosa

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

Article References: Meneguzzo, P., Di Pascoli, L., Rossi, A., Munno, V., Montagnese, S., Veronese, A., Sala, A., & Favaro, A. (2026). Beyond body mass index: associations between phase angle, vector-derived bioelectrical markers, and selected hematological and physiological alterations in anorexia nervosa. Eating and Weight Disorders – Studies on Anorexia, Bulimia and Obesity. https://doi.org/10.1007/s40519-026-01912-x

Image Credits: AI Generated

DOI: 10.1007/s40519-026-01912-x

Keywords: anorexia nervosa, phase angle, bioelectrical impedance, body mass index, hemoglobin, hematocrit, blood pressure, alanine aminotransferase, body composition, eating disorders, Beyond, body