Preoperative Phase Angle as a Marker of Nutritional and Functional Vulnerability in Patients Undergoing Colorectal Cancer Surgery: A Prospective Observational Cohort Study

Background/Objectives: This study evaluated whether phase angle (PhA) was associated more strongly with nutritional and functional vulnerability than with postoperative morbidity. Methods: This cohort included 207 adults undergoing colorectal cancer surgery. Primary outcomes were malnutrition defined according to the Global Leadership Initiative on Malnutrition (GLIM) criteria, low handgrip strength and impaired Short Physical Performance Battery (SPPB) scores; postoperative complications, readmissions and length of stay were exploratory outcomes. PhA was measured by 50 kHz bioelectrical impedance vector analysis. Analyses estimated areas under the curve (AUCs) with 95% confidence intervals and Youden cut-offs; models adjusted for age, sex and body mass index. Results: PhA was lower in participants with nutritional vulnerability than in those without it (4.57 ± 0.62° vs. 5.20 ± 0.69°; p < 0.001). Discrimination was excellent for handgrip strength <10th percentile (AUC 0.803) and acceptable for SPPB < 10 (AUC 0.785), SPPB ≤ 6 (AUC 0.761) and GLIM-defined malnutrition (AUC 0.728) but showed no discrimination for any postoperative complication (AUC 0.507). After adjustment, PhA ≤ 4.7° remained associated with GLIM-defined malnutrition, handgrip strength < 10th percentile and SPPB < 10 but not with any postoperative complication. Conclusions: PhA was more strongly associated with nutritional and functional vulnerability than with postoperative morbidity. Thresholds require external validation; PhA may complement, not replace, GLIM, body composition, handgrip strength and SPPB.