The present study aims to report a five-step nutritional intervention conducted by a multidisciplinary care team as well as to investigate its effects on the nutritional status and quality of life of gastroenteric cancer patients undergoing chemotherapy. A total of 176 patients with newly diagnosed gastroenteric cancer were enrolled in the observational study. The nutritional status of the patients was assessed using Patient-Generated Subjective Global Assessment (PG-SGA) and Nutritional Risk Screening-2002 (NRS-2002), and anthropometry and biological tests were performed. Patients were randomly divided into intervention group (n = 40) and control group (n = 38). Patients in the intervention group received five-step nutrition intervention, while the control group received routine nutrition management. In the newly diagnosed patients with gastroenteric cancer, 50% presented mild to moderate malnutrition, 29.5% presented severe malnutrition, while only 20.5% of patients were in good nutritional status. Nutritional interventions reduced the progression of malnutrition after 10 weeks. Anthropometric parameters increased as well as function and symptoms improved; therefore, controlled the decline in quality of life. To sum up, five-step nutritional interventions conducted by a multidisciplinary care team improved the nutritional status of patients with gastroenteric cancer undergoing chemotherapy, and showed positive impacts on quality of life.