A healthy diet can maintain a normal body weight, enhance the body’s ability to resist cancer and maintain normal physical strength, as well as the rehabilitation of body tissues affected by cancer. For cancer patients, a healthy diet can enable them to better tolerate the side effects of various anti-tumor treatments and actively receive various anti-tumor treatments, thus also improving their chances of survival. The basic principle of diet for cancer patients is to consume carbohydrate foods rich in low fat, and at the same time ensure adequate intake of protein. Carbohydrates: In food, the main source of energy is carbohydrates (sugar), accounting for 55~60% of the food calories in a day, most of which come from polysaccharides in food, which are often found in cereals, beans, sweet potatoes and some vegetables. When there are not enough carbohydrates in the food, proteins in the body become a source of energy. Fats: It is well known that fats are closely associated with diseases of the cardiovascular system. The relationship between fat and cancer is not well understood. But there are some studies that link fat to cancer, especially colon cancer and prostate cancer. Many health experts believe that the calories produced by fat in a day should be limited to 20~50%. Protein: Protein is one of the indispensable substances in the body, which plays a role in maintaining, repairing and regenerating the body cells, therefore, for cancer patients, it is necessary to increase the intake of protein during the anti-tumor treatment. Protein should account for 15~25% of the total calories in 1 day. Vitamins: Cancer and anti-tumor treatment will affect the absorption of some vitamins, especially vitamin B, so it should be supplemented appropriately. It has also been suggested that vitamin C, vitamin E, etc., can prevent cell destruction and thus reduce the risk of cancer. These vitamins are mainly found in brightly colored foods, for example: carrots, citrus, green peppers, etc. are rich in vitamin C, while green vegetables, bread, etc. are rich in vitamin E. 1. Nutritional Therapy for Cancer Patients During the cancer treatment as well as the recovery period, a healthy diet that can maintain the body balance plays a very important role in enhancing the patient’s physical strength and increasing the cure rate of the tumor. Generally speaking, once patients know they have cancer, most of them will change their diet immediately. For example, according to the results of a survey on a group of women with breast cancer, 70% of the patients changed the content of their diets, and 80% of them began to take vitamins or other nutrients. But food is not medicine. Although there is a certain relationship between the patient’s health status, diet and nutrition and the cure rate of tumors, there is no evidence that specific food and nutritional programs can lead to remission and cure of cancer. The interrelationship between diet therapy and cancer is very complex, and it is currently believed that diet therapy may play a greater role in the prevention of cancer. 2. Calorie counting Usually only people who are ready to lose weight pay attention to the calorie intake in a day. However, for cancer patients, calorie intake in a day should be calculated in order to maintain weight or gain weight. The easiest way to calculate calories in a day is to multiply the current body weight (K) by the necessary calorie coefficients according to gender and metabolism (women: 20~30Kca1, men: 25~35Kca1). Before and after surgery or during fever, the intake of 1 kg of body weight should be increased to 40~50 Kca1. For example, for a 60 kg woman, i.e., 60×20~30=1200~1800 Kca1, the calories needed to maintain body weight in a day are 1200~1800 Kca1; an 85 kg man needs 2125~2975 Kca1 calories in a day. 3.Correct understanding of weight loss More than 50% of cancer patients have different degrees of weight loss, of which about 15% of patients have weight loss of more than 10%. Two thirds of the patients with progressive cancer may have malignant fluid. In general, patients with weight loss have a poorer prognosis than those who are able to maintain their weight. However, it is not known whether weight loss directly affects survival. Weight loss is one of the symptoms of cancer progression, so it should be said that the shortened survival of the patient is due to the disease itself and not due to weight loss. In order to maintain body weight, it is necessary to consume food that is calorie dense and to be able to digest the food and absorb adequate nutrients. The malignant state directly affects the patient’s immune system, and on top of that, once malnourished, the functioning of the digestive system is compromised, which further worsens the condition of the body. For cancer patients, if there is obvious weight loss due to the side effects of anti-tumor treatment, anti-tumor treatment must be stopped immediately. 4.Secondary loss of appetite The loss of appetite in early stage cancer patients may be due to depression, emotional instability or side effects of anti-tumor treatment. In fact, the diagnosis of cancer is a very scary thing, and at the same time, due to the anti-tumor treatment affects the daily life routine, coupled with the emotional upset, depression and so on, resulting in loss of appetite is very common. Pain may also significantly affect appetite. When the brain feels unpleasant experiences, it is less responsive to other stimuli, such as the aroma of food. Dysfunction of the digestive system may significantly affect the state of the cancer patient. Certainly if the tumor presses on some organs of the digestive system, or if the cancer directly invades organs related to digestion, the normal transport of food, the absorption of nutrients, or both are affected. For example, tumors of the oral cavity or pharynx affect chewing and swallowing movements; tumors of the stomach or intestines prevent the passage of food and reduce the production of digestive juices, thus affecting the absorption of food; tumors of the liver or pancreas may lead to a deficiency of digestive enzymes. Dysfunction of the digestive system may lead to a feeling of fullness, which is caused by tumors that reduce the size of the stomach; slowing the passage of food through the digestive system, etc. The feeling of fullness is one of the symptoms of worsening cancer.