Background: Disease-related malnutrition and sarcopenia are prevalent conditions in gastrointestinal cancer patients, whose early diagnosis is essential to establish a nutritional intervention that contributes to preventing adverse outcomes and improving the disease prognosis. Phase angle (PhA), rectus femoris cross-sectional area (RFCSA) and rectus femoris thickness (RF-Y-axis) are considered effort-independent markers of muscle mass, strength and functionality. These markers are influenced by the metabolic changes in cancer patients but have not been fully validated in this population. Objective: This study aimed to evaluate the potential utility of PhA, RFCSA and RF-Y-axis in predicting malnutrition and sarcopenia in patients with esophagogastric cancer (EGC). Methods: This was a cross-sectional study of patients diagnosed with EGC. PhA was obtained using bioelectrical impedance vector analysis (BIVA), along with ASMMI. RFCSA and RF-Y-axis were measured via nutritional ultrasound (NU®). Muscle capacity was assessed using handgrip strength (HGS), and functionality by applying the Short-Physical-Performance-Battery (SPPB). Malnutrition and sarcopenia were determined according to GLIM and EWGSOP2 criteria, respectively. Results: Out of the 35 patients evaluated, 82.8% had malnutrition and 51.4% sarcopenia. RFCSA(r=0.582) and RF-Y-axis(r=0.602) showed significant, moderate correlations with ASMMI, unlike PhA(r=0.439), which displayed a weak correlation with this parameter. However, PhA (OR=0.167,CI 95%:0.047-0.591,p=0.006), RFCSA (OR=0.212, CI 95%:0.074-0.605,p=0.004), and RF-Y-axis (OR=0.002,CI 95%:0.000-0.143,p=0.004) all showed good predicting ability for sarcopenia in the crude models, but only RF-Y-axis was able to explain malnutrition in the regression model (OR=0.002, CI 95%:0.000-0.418,p=0.023). Conclusion: RF-Y-axis emerged as the only independent predictor of both malnutrition and sarcopenia in this study, likely due to its stronger correlation with ASMMI compared to PhA and RFCSA.