For patients with malignant tumors who are undergoing chemotherapy or even need further surgery or radiotherapy, the importance of maintaining good nutritional status cannot be overstated. Clinical nutrition therapy is gradually becoming an important component of oncology treatment and is driving dramatic changes in medical oncology clinics. For the nutritional support of malignant tumor patients, there are still some controversies, mainly throughout the malignant tumor patients need nutritional support, how to determine the object of nutritional support. First, a few principles of nutritional therapy for patients with malignant tumors: 1. There is no evidence that nutritional support promotes tumor growth Over the years, no nutritional support has been found to promote tumor growth in clinical practice. On the contrary, there is evidence that actively carrying out nutritional support for malnourished tumor patients can reduce complications and improve the quality of life. 2. Patients with malnutrition and long-term inability to eat or insufficient absorption of nutrients should be given nutritional support appropriately. 3. Nutritional support is usually rarely used in palliative support of end-stage tumor patients. Only a few patients may benefit, such as: expected survival more than 4060d; KPS score more than 50; no serious organ dysfunction. However, adequate communication and cooperation with family members and patients are required. 4, well-nourished surgery, chemotherapy and radiotherapy patients do not need to routinely use nutritional support Patients with malignant tumors have a significant increase in body energy consumption, accelerated lipolysis, increased visceral protein consumption, and decreased protein synthesis rate and increased catabolic rate. The disease itself and the adverse effects of chemotherapy not only inhibit the patient’s nutrient intake and absorption, but also cause the patient’s body to be in a state of stress, and the catabolism increases significantly. The use of nutritional therapy to ensure that the patient’s body daily intake of sufficient calories and nutrients can meet the body’s activities, tissue repair and renewal, maintain normal metabolism, improve the nutritional status of the body and organ function, and improve the tolerance of chemotherapy, while the tumor tissue is still proliferating according to its own biological characteristics. If the supply of exogenous nutrient matrix is insufficient, the tumor tissues will strengthen the direct acquisition of nutrients from the host normal tissues to meet their rapid growth needs, further aggravating the degree of metabolic abnormality of the organism. Obviously, insufficient supply of nutrients is obviously harmful to the organism, but the tumor suppression effect is not great. Nutritional support for malignant tumor growth support evidence is insufficient. The incidence of malnutrition in tumor patients is high, and malnutrition is often accompanied by malnutrition in patients with malignant tumors, which is particularly common in digestive tumors such as gastric cancer, pancreatic cancer, and colon cancer. The incidence of malnutrition in patients with malignant tumors is as high as 40% to 80%. The incidence of weight loss and malnutrition in patients with esophageal cancer is as high as 80%. Cancer cachexia occurs in about 30%~85% of tumor patients, and the most prone to cachexia are gastric cancer, pancreatic cancer and esophageal cancer patients, about 80%; about 60% of colorectal cancer patients have cachexia. Nutritional undernutrition and nutritional risk in oncology patients are very prominent, and nutritional risk screening is an important tool for identifying nutritional problems in oncology patients, but there is no “gold standard” tool for oncology patients at present. The PG-SGA is the preferred method of nutritional screening for oncology patients recommended by the American Society of Dietitians and Nutritionists (ASPEN). The PG-SGA has two components: first, past body mass, symptoms of disease, past and current food intake, and physical activity status; and second, metabolic status, diseases that can affect nutritional status, and their physical examination. The higher the score, the higher the nutritional risk. The following types of patients should pay special attention to nutritional therapy: 1, nutritional therapy for chemotherapy patients Chemotherapy causes obvious digestive reactions such as nausea and vomiting, abdominal pain and diarrhea, and digestive mucosal damage, which seriously weaken the patient’s appetite and affect the eating. Malnutrition reduces the tolerance of chemotherapy and affects the implementation and efficacy of chemotherapy. Nutritional therapy can provide a good metabolic environment for chemotherapy, and at the same time, chemotherapy to reduce or remove the tumor load will play a role in moderating or eliminating the “source” of abnormal metabolic state, and the nutritional status of the patient will undergo rapid and obvious changes, so chemotherapy and nutritional therapy obviously complement each other. Nutritional therapy during chemotherapy should be based on the prevention and treatment of tumor-related malnutrition or cachexia, improving the tolerance of chemotherapy, slowing down the damage caused by chemotherapy-related side effects on the body, and improving the quality of survival of patients, so it is not necessary to routinely carry out nutritional therapy, and to do a good job in nutritional risk screening, and nutritional support is only given to those who are obviously malnourished (weight loss) and those whose intake of food is seriously affected by chemotherapy. In order to minimize the metabolic burden on the body, calorie and nutrient supplementation should be the difference between actual and theoretical intake. For those with unstable vital signs and multiple organ failure, systematic nutritional therapy is no longer considered to avoid increasing the metabolic burden of the patient. 2.Patients with chronic mechanical malignant intestinal obstruction Chronic mechanical malignant intestinal obstruction is a common complication in medical oncology, mostly caused by gastric cancer, intestinal cancer and ovarian cancer. Nutritional treatment: conventional treatment: fasting and gastrointestinal decompression, enema, etc.; extra-gastrointestinal nutritional support: improving nutritional status and abnormal metabolic status of patients; eliminating inter-tissue edema of digestive tract wall; inhibiting secretion of digestive tract glands; actively treating the primary disease. 3, esophageal cancer patients: Nutritional treatment ideas for esophageal cancer chemotherapy patients: correct or improve patients’ nutritional status, improve the body’s tolerance to chemotherapy; for those with normal gastrointestinal function, gastrointestinal tube feeding supplemented with enteral nutritional preparation is the mainstay. For those with loss of gastrointestinal function, parenteral nutrition is preferred, and once recovery is good, trans-intestinal nutrition is used as much as possible, and oral feeding is encouraged; it is emphasized that nutritional evaluation must be made before, during and after chemotherapy in each case, as well as nutritional therapy when necessary. 4.Patients with cancer cachexia Decrease in calorie and nutrient intake, and the tumor produces a variety of pro-inflammatory factors that consume fat and muscle leading to progressive weight loss, which is called cancer cachexia. Metabolic regulation is to reduce catabolism and promote protein synthesis by using drugs, biologics and tissue-specific substances to intervene in the metabolic process of human nutrients. Therefore, the use and exploration of metabolic conditioning therapy is essential for reversing malignant disease in malignant tumors.