The causes of wasting in cancer patients can be divided into two categories: the first category is the consumption caused by the cancer itself, and the consumption of cancer patients is also significantly greater than that of normal patients. It can be simply assumed that a large part of the nutrients absorbed by the body are absorbed and consumed by the cancer cells in the body, so cancer patients will become thinner and thinner. The second category is the wasting caused by cancer-related complications. The growth rate of cancer is significantly faster than normal tissues, and the most common one is digestive tract cancer. Patients with advanced digestive tract cancer cannot eat or lack of appetite, which leads to a significant decrease in nutrient intake, and the absorption of nutrients will also be greatly hindered, so the patients’ wasting is very obvious and even presents a cachectic state. Cancer patients will suffer from nausea, vomiting, diarrhea and other complications as a result of chemotherapy, which will not only reduce food intake, but also reduce nutrient absorption, and serious vomiting and diarrhea will also lead to increased nutrient loss, all of which will cause patients to become thinner and thinner. In conclusion, wasting of cancer patients is a very common phenomenon, which not only affects the treatment effect of patients, but also has a great impact on the survival time of patients, so nutritional support treatment for cancer patients is very important.