I. Importance of nutritional therapy for tumor patients Both tumor itself and anti-tumor treatment will have a great impact on patients’ eating and body energy metabolism, and reduce their nutritional level, so taking proper nutritional therapy is crucial for tumor patients. Although medical research has not yet found that nutritional therapy can prolong the survival time of patients, there are a lot of data showing that proper nutritional therapy can make patients keep their strength, maintain their weight and feel comfortable, and have improved tolerance to anti-tumor therapy, and also reduce the occurrence of infection. The main objectives of nutritional therapy are as follows: 1) to prevent and treat malnutrition or cachexia; 2) to improve patients’ tolerance to anti-tumor therapy; 3) to control the side effects of anti-tumor therapy; 4) to improve patients’ quality of life. Of course, since the physical condition of each patient is different, it is necessary for doctors to set appropriate nutritional treatment goals according to each individual. Main nutritional elements and micronutrients. Nutritional elements involved in nutritional therapy can be divided into two categories. They are major nutrients and micronutrients. （Protein is mainly found in milk, meat, eggs, fish, beans and other foods. Protein is the most important nutrient that constitutes human tissues and is the main transporter of substances in the body. The main functions of protein include energy supply, regulating physiological functions, maintaining human growth and development, and is the main material for constituting and repairing cells and tissues. If protein intake is not enough, the body can only be forced to dig internally to meet its own nutritional needs by breaking down muscles, which will undoubtedly greatly deplete the fighting power of cells, slow down the speed of disease recovery and reduce the body’s resistance to infection. Therefore, for tumor patients, no matter after surgery or radiotherapy, they need to get more protein than general patients to repair tissues and resist infection. 2.Carbohydrates Carbohydrates, also called sugars, are widely found in fruits, vegetables and grains. It is the main source of caloric energy for human daily life, providing enough energy for muscle activity and maintaining the physiological functions of organs. Fiber is also a kind of carbohydrate, the human body intake of fiber can help intestinal peristalsis, keep the stool loose, in order to facilitate the discharge, and can not be digested by the body. 3, fat Fat is another major source of body heat, the body will use its energy by breaking down fat to maintain body temperature and transport some fat-soluble vitamins in the body. Fats can be divided into two categories – saturated fatty acids and unsaturated fatty acids. Unsaturated fatty acids can be further divided into monounsaturated and polyunsaturated fatty acids. Among them, monounsaturated fatty acids are mainly found in vegetable fats and oils, such as olive oil, canola oil, peanut oil and other middle; while polyunsaturated fatty acids are mostly found in sunflower oil, corn oil, flaxseed oil and seafood. For example, we often talk about fish oil (ω)-3 polyunsaturated fatty acids), whose main components, eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), are important nutrients that cannot be synthesized by the human body itself but are indispensable to enhance the immunity of the body and improve the tolerance of tumor patients to radiotherapy. Saturated fatty acids are mainly found in animal fats, such as pork, poultry, milk, cheese and butter, and some vegetable fats, such as coconut oil and palm kernel oil, are also saturated fatty acids. Excessive intake of saturated fatty acids can raise blood cholesterol levels and increase the risk of heart disease, so generally speaking, their daily intake should be limited to less than 10% of total energy. Trans fatty acids are also part of the saturated fatty acid family, and are mostly found in foods containing margarine, such as cakes, and in some animal products, such as dairy products. As a child of the fat family, trans fatty acids often cause trouble and interfere with the balance of cholesterol in the body, so they should be avoided as much as possible in the daily diet. It is generally accepted in medicine that unsaturated fatty acids are better than saturated fatty acids or trans fatty acids from the perspective of heart protection and cholesterol reduction. (ii) Micronutrients Micronutrients are nutrients that are less in demand by the human body, mainly including vitamins, minerals and antioxidants. Vitamins and minerals Vitamins and minerals are important micronutrients that the human body needs to maintain normal function. We mostly get vitamins and minerals from natural foods, and in addition, we can also get them in the form of taking supplements. In most cases, people with a balanced dietary intake are able to get sufficient energy and protein, as well as adequate vitamins and minerals. However, oncology patients, especially those who receive long-term anti-tumor treatment, their balanced dietary structure is usually disrupted. As a remedy, doctors usually prescribe daily vitamin and mineral supplements for oncology patients. However, some tumor patients blindly take a lot of vitamins and minerals and some other anti-tumor prescriptions with inaccurate efficacy in order to improve immunity and kill tumor cells, not knowing that taking such a large amount of certain or some trace elements is actually harmful to human body and not only cannot get the expected effect, but also will even weaken the efficacy of radiotherapy, so it is not advisable. Therefore, tumor patients should consult their doctors before taking non-medically prescribed health supplements, and should not act blindly. 2. Antioxidants Antioxidants include vitamins A, C and E, as well as selenium and zinc. These elements can combine with free chemical groups, thus changing their properties and preventing them from attacking normal cells in the body. Fruits and vegetables are natural sources of antioxidants, and patients can consume a certain amount of antioxidants by eating more of these foods. However, it is not usually advisable for patients to consume large amounts of antioxidants or vitamin-enhanced foods during radiotherapy, so it is best to consult a doctor before starting antioxidants.