The recovery of cancer patients is related to multiple factors such as treatment, nursing care, nutritional care, physical activity, and psychological factors. Before the start of anti-cancer treatment, during treatment and after treatment, proper diet and nutrition not only help patients feel better and stronger, but also help improve patients’ tolerance and efficacy of treatment and promote damaged tissue repair. Poor nutritional status not only affects patients’ physical fitness and quality of life, but also may affect the treatment effect, for example, malnourished patients receiving chemotherapy may need to reduce the chemotherapy dose, and surgery combined with malnutrition is not only easy to complicate infection, but also may lead to complications such as delayed wound healing. Due to the disease itself and side effects of treatment, tumor patients encounter more problems in diet and nutrition, so they need more professional guidance on diet and nutrition. This article introduces the general dietary principles and common problems for tumor patients for their reference. Balanced diet and food diversification can provide the best ratio of nutrients to the body, which is the basis and guarantee to maintain the health and good functional status of the body. To achieve a balanced diet, we can refer to the “Dietary Guidelines for Chinese Residents” and the “Balanced Diet Pagoda for Chinese Residents” formulated by the Chinese Nutrition Society to reasonably select and match foods and exchange them with each other to make a rich and balanced diet. According to the balanced diet pagoda, excluding water and oil and salt at each meal, there are three major types of food to ensure balanced nutrition: firstly, cereals, potatoes and beans (rice, noodles, grains, potatoes, sweet potatoes and red beans, etc.), secondly, meat, eggs, milk, soybeans, nuts and products (including eggs, fish and shrimps, poultry and animal meat, tofu, yogurt and walnuts, etc.), and thirdly, vitamins, trace elements and minerals. The third is the main provision of vitamins and trace elements, minerals, vegetables and fruits (including leafy vegetables, root vegetables, fresh beans, vegetables such as eggplant, fruits and vegetables, aquatic plants, potatoes and potatoes, and fruits such as citrus, berries, nuts and fruits). The above food intake should be adjusted according to individual height and weight and activity level. According to the Dietary Guidelines for Chinese Residents, the recommended daily food intake per person is as follows: 150-300 grams of cereals and potatoes (dry weight); 300-500 grams of non-starchy vegetables; 200-400 grams of fruits; 100-175 grams of fish, shrimp, meat and poultry, 1/2-1 egg, 300 grams of milk, 300 grams of soybeans and nuts 30-50 grams, oil 25-30 grams (30-45 ml), salt 4-6 grams. If the metabolic characteristics of tumor patients are taken into consideration, tumor patients can reduce carbohydrates and increase the proportion of vegetable fats intake appropriately. If you need more personalized dietary guidance, you can consult with an experienced dietitian. Most tumor patients may experience surgery, radiotherapy, chemotherapy, biotherapy and other treatments, and the side effects of both surgical trauma and radiotherapy may lead to stress, increased consumption, increased free radicals in the body and decreased immunity. Therefore it is necessary to increase the intake of protein-rich (by 50%) and antioxidant vitamins and trace elements foods based on a balanced diet as appropriate. Protein can help repair damaged tissues and cells and improve immunity, while antioxidant vitamins and trace elements can prevent excessive free radicals from damaging normal tissues of the body. Common protein-rich foods include: eggs, milk and products, soybeans and products, chicken, duck, fish and nuts. Foods rich in antioxidant vitamins and trace elements include: various fresh vegetables and fruits (dark vegetables, spinach, broccoli, tomatoes, asparagus, radish, fresh beans, lotus root, eggplant, shiitake mushrooms, onion and garlic, citrus, apple, kiwi, mango, papaya, sage fruit, etc.), whole grains (oats, millet, sorghum, barley, black rice, corn), nuts and seeds (walnuts, hazelnuts, almonds, sunflower seeds sesame seeds), potatoes, eggs, yogurt, etc. It is important to note that the intake of protein should not be excessive, otherwise it may increase the burden on the kidneys, especially for patients with poor kidney function. It is also not recommended to increase too much red meat, as too much red meat may increase the risk of intestinal tumors (no more than 500 grams per week is recommended). For antioxidant vitamin and micronutrient supplementation it is recommended to supplement with a wide variety of fresh vegetables and fruits, which are the best sources of these nutrients (high dose antioxidant vitamin tablets are not recommended as they may have some side effects). In terms of cooking methods, a combination of raw food, quick blanching in boiling water and steaming is recommended, because some phytochemicals such as lycopene and carotene can increase their antioxidant activity after steaming instead, while long time stewing tends to inactivate or lose antioxidant vitamins. If pain, nausea, vomiting, anorexia, depression, insomnia and other symptoms occur, you can ask your doctor to prescribe some symptomatic medications, such as antiemetic, anti-pain medication, methotrexate, anti-anxiety medication and so on. You can also ask an experienced herbalist to prescribe some herbal medicines for improving appetite and immunity. For patients with poor appetite and indigestion, B vitamins and digestive enzymes and probiotic preparations can be supplemented, and appetizing and digestive foods such as hawthorn, grain and wheat germ, white radish, yogurt, yam, etc. can be used. For most patients with poor appetite, a small number of multiple meals is better than 3 large meals, and you can always have some additional small foods on hand, such as sesame crackers, baked bun pieces, bread, fruits, fruit juices, yogurt, nuts, etc. Don’t wait until you are hungry, especially don’t accept treatment on an empty stomach. Eating some light food an hour before treatment can increase the tolerance to treatment, and eat the biggest meal when you are most hungry. Choose more foods that are light and well digested while high in nutrient density such as high energy and protein, such as soft rice, noodles, dumplings, buns, low-fat yogurt, egg custard, tofu, boiled balls, stewed meat, green leafy vegetables, freshly squeezed orange juice, etc. Drink soup and water between meals or 30 minutes before meals, as too much water at meals can make you feel full early and is not good for digestion. If the side effects are too great, don’t force to eat. You can let your digestive tract rest properly when your appetite returns and then try to eat normally, but pay attention to hydration and electrolytes. Make sure 8-10 glasses of water (2000-3000ml) per day. Physical activity during anti-cancer treatment can bring you many benefits, such as helping to maintain muscle strength and bone hardness, improving stamina, reducing stress, treating depression, relieving constipation, etc. If your physical strength or your doctor allows, you can take a 30-minute walk every day and exercise more than 5 times a week. If your physical strength is poor, you can also start with 5-10 minutes of exercise per day and gradually increase the amount of exercise until you reach the goal of 30 minutes of exercise per day. In general, except for the drugs that are being taken which need to be avoided according to medical advice, it is not recommended to avoid excessive avoidance of food to avoid affecting the nutritional balance. Most patients need to restrict or avoid foods such as high temperature fried, smoked and barbecued, spicy and stimulating, greasy and hard foods. Patients with low white blood cells should avoid eating raw, unpasteurized foods such as unpasteurized milk, vegetables and fruits that have not been carefully washed. There are multiple ways to supplement nutrition If a patient has greater difficulty eating, eats too little for more than 7-10 days, and is expected to be unable to eat for more than 7 days. The patient may need nutritional support to maintain or improve nutritional status. Routes of nutritional support include enteral and parenteral nutritional support. This means supplementation with nutrient-comprehensive enteral and parenteral nutritional preparations via enteral or intravenous routes. For example, for patients who have difficulty in swallowing due to esophageal edema and other reasons, food can be made into homogenized meal orally by blender, or some enteral nutrition preparations can be supplemented by oral or tube feeding. In case of severe intestinal dysfunction, such as complete intestinal obstruction, severe diarrhea, and gastrointestinal bleeding, patients may need to supplement nutrition through intravenous nutrition. In addition, for patients who are mildly underfed, high-calorie-high-protein enteral nutrition preparations can be chosen as additional food, which is useful to improve the nutritional status as soon as possible. Department of Clinical Nutrition, Peking University Cancer Hospital