Diet is one of the most important concerns of tumor patients. Many people worry that eating more will promote the growth of tumor cells and hope to starve them to death by starvation. It is true that tumor cells grow and proliferate by taking in nutrients from the body, but even in the advanced stage of tumor when patients have difficulty in eating, tumor cells will not stop growing because the host eats less. In the war of competing with normal cells for nutrients, tumor cells will always be the winner. With excessive starvation, the first to be damaged are normal cells and tissues. Once malnutrition occurs, the tolerance of subsequent radiotherapy will become poor, complications will appear, prognosis will be poor and survival time will be short. Therefore, tumor patients should eat normally to ensure the normal nutritional needs of the body. However, normal eating is not equal to excessive nutrition, eight or nine minutes full is enough. The dietary principle of tumor patients should be high fat, high protein and low carbohydrate. Tumor patients should eat less sweet food, such as drinks, cookies, cakes, snacks, ice cream, etc., because tumor cells mainly rely on decomposing carbohydrates to grow and reproduce. Reducing the intake of carbohydrates creates an environment unfavorable to the growth of tumor cells, which has a positive effect on the prevention and treatment of tumors. Tumor patients can eat a small handful of nuts every day. Tumor cells are less capable of using fat, while normal cells can make full use of fat for energy. There is no scientific basis for the so-called “hairy foods” such as meat, eggs and milk. If you are not allergic to such foods, not only do you need to avoid eating them, but you should eat them in moderation every day, which can help tumor patients improve their nutritional status, enhance their immunity and improve their quality of life. Tumor patients with inadequate daily diet should prefer enteral nutrition for oral supplementation, instead of believing in “Cordyceps”, “Bird’s Nest”, “Ginseng”, “Lingzhi” and other expensive foods, It is recommended that tumor patients should prefer oral supplementation with intra-intestinal nutrients instead of superstitiously taking “Cordyceps”, “Bird’s Nest”, “Ginseng”, “Lingzhi” and other precious supplements. It is recommended that tumor patients regularly go to the hospital to receive nutritional assessment and guidance from nutritionists and develop good eating and weight recording habits. Nutritional therapy cannot cure cancer, but it can change the nutritional status of patients, thus improving body function and immunity, reducing the side effects of radiotherapy, increasing patients’ tolerance to radiotherapy and improving quality of life.