Chemotherapy is indispensible for patients suffering from advanced gastric or colorectal cancer, and also the main therapy for those with end-stage tumor. However, incidence of malnutrition during chemotherapy was reported as high as 60%. The mechanisms include anatomy modification of digestive tract, side effects of chemotherapy such as anorexia, nausea, vomiting, and inflammatory factors generated or induced by the tumor. Malnutrition may lead to discontinuation of the therapy, compromise of the anti-cancer effect, increase of toxicity and mortality. 20%-40% of patients with end-stage tumor ultimately died from malnutrition.