I. Diet and nutrition treatment In daily life, we should adopt a prevention-oriented approach to gastrointestinal tumors, supply a balanced diet, eat more health foods with cancer prevention effects, all foods should be fresh, and should not eat hard, spicy, vegetables containing nitrosamines, salted fish, bacon and other foods, not eat moldy, overheated and rough foods, chew and swallow slowly when eating, and pay attention to water hygiene. Supplement sufficient vitamin A, vitamin B1, vitamin B1. and vitamin C, as well as zinc, selenium and other trace elements, and the diet should contain a certain amount of dietary fiber. For patients with gastrointestinal cancer, the requirement of preoperative dietary treatment is to make good preoperative preparation. If patients with esophageal cancer or gastric cancer have difficulty in swallowing, or have foreign body sensation in the esophagus, or have symptoms such as stomach pain and fullness after eating, it is appropriate to use homogenous diet to supplement sufficient calories and various nutrients, or high-protein liquid diet to prevent the occurrence of wasting, anemia, low plasma protein disorder, etc. When colon (rectal) cancer has blood in stool, attention should be paid to give semi-liquid diet with less residue and high protein to increase nutrition and improve immune function of the body; for patients with obvious emaciation and anemia, it is appropriate to supply appropriate nutrition according to standard weight, and for those with swallowing difficulty and insufficient food, intravenous nutrition or elemental diet should be supplemented. The postoperative diet is usually supported by intravenous nutrition within 4 d after surgery, or with jejunostomy tube drip nutrition solution, and then gradually eat half amount of clear liquid through the mouth, and then full amount of clear liquid. If no combined anastomotic fistula occurs, the patient’s general condition can be taken into account and a semi-liquid diet with less residue can be given for about 14 d. Later, the quality and quantity of the diet can be gradually increased. There are also advocates for the use of jejunostomy tube immediately after surgery to drip nutrient solution, after the recovery of intestinal function can be dripped into 5% glucose solution, or 5% glucose saline for a trial meal, if there is no diarrhea and other reactions, start to increase the drip of rice soup, later can be dripped elements of diet, homogenous diet, etc.. And gradually increase the amount of nutrition dripped into the fistula and reduce intravenous nutrition. After the fistula is completely closed, you can eat a semi-liquid diet or a liquid diet with a small number of meals. Third, radiotherapy and chemotherapy diet treatment Radiation therapy is a regional treatment that is administered in dozens of fractions to treat the disease and is usually not very reactive and is tolerated by the patient. Radiotherapy will consume some physical and thermal energy, therefore, attention should be paid to nutritional supplementation during radiotherapy to ensure sufficient protein and thermal energy. Except for the abdomen, where there may be loss of appetite and even nausea and vomiting, there is no significant loss of appetite in other parts of the body, so there is no need to restrict the diet too much. Radiation therapy can cause esophageal mucous membrane congestion and edema, swallowing difficulties, according to the patient’s swallowing situation, with light, less oily thick liquid diet, such as milk with eggs, lotus root powder with eggs, batter with eggs, crumbled noodles, etc., or with homogenized diet. In short, make the food processed and cooked into extremely fine and soft, easy to swallow, and easy to digest and absorb, and attention should be paid to the supplementation of vitamins, minerals and trace elements. Patients with upper gastrointestinal symptoms are often significantly worse when using chemotherapy than before chemotherapy, often with anorexia, nausea, vomiting, reduced appetite and reduced food intake. Therefore, it is advisable to adjust the diet nutrition to a better state before carrying out chemotherapy. In order to increase the resistance of the organism, the elemental diet can be appropriately supplemented. It is also advisable to give light and less oily thick liquid, semi-liquid, or homogenous diet to maintain nutrition, so that the patient can tolerate chemotherapy. The effect of radiation injury on nutritional metabolism involves calories, carbohydrates, lipids, proteins, vitamins, minerals and trace elements, and the degree of effect is related to the severity of radiation injury.