Nutritional support therapy for tumor patients has become an important part of multidisciplinary comprehensive treatment for malignant tumors. Evidence-based medical research shows that nutritional support therapy plays an important role in the process of tumor surgery, chemotherapy and radiotherapy. Unlike anti-tumor treatments such as surgery, radiotherapy, chemotherapy and molecular targeted drug therapy, nutritional support therapy has no direct effect on killing tumor cells, but improving the nutritional status of tumor patients can improve immune function, correct organ insufficiency, greatly improve patients’ tolerance to chemotherapy and radiotherapy, and help to complete the established treatment plan. Therefore, oncologists and nutritionists need to join hands to promote its research and development. The prevalence of nutritional metabolism abnormalities in tumor patients Clinical studies have found that people suffering from malignant tumors are among the high-risk groups for malnutrition. The reason for malnutrition in tumor patients is the abnormal nutritional metabolism in the body, which is mainly manifested by the abnormal changes of carbohydrate, protein and fat metabolism. First of all, lactic acid cycle accounts for 20% of glucose conversion in normal people, but in tumor patients, lactic acid cycle can increase to 50%, accounting for 60% of total lactic acid, which eventually leads to a large loss of carbohydrates. In addition, the main reason for the occurrence of cachexia in patients with advanced tumors is the loss of endogenous nitrogen in skeletal muscle leading to altered protein metabolism, followed by the production of inflammatory mediators leading to the occurrence of malnutrition in the organism. One of the main features of tumor cachexia is fat consumption, and the abnormal alteration of fat metabolism in tumor patients is related to certain cytokines and metabolic factors, but the exact mechanism of malnutrition occurrence in tumor patients has not been fully elucidated yet. In recent years, a large number of clinical studies have shown that malnutrition in tumor patients significantly endangers the survival and quality of life of tumor patients, reduces the effectiveness of tumor treatment and increases the toxic side effects of chemotherapy and radiotherapy. Therefore, the nutritional support for tumor patients must be emphasized in the comprehensive treatment of tumor. Improving the nutritional status of tumor patients can greatly improve the tolerance of patients to chemotherapy and radiotherapy, facilitate the completion of the established treatment plan and make the tumor treatment measures play a more powerful role, and this emerging discipline of tumor nutrition is being widely emphasized and developed by clinical scholars. At present, it is not considered that diet therapy alone can achieve anti-tumor efficacy, but it can help improve patients’ nutritional status, enhance immune function and correct organ insufficiency, and nutritional support can become an important part of comprehensive tumor treatment. The development direction of nutritional support therapy is immunonutritional therapy, and the addition of certain immune-enhancing ingredients such as glutamine and unsaturated fatty acids in nutritional formulas is gradually gaining attention. Nutritional risk screening and nutritional status assessment Nutritional support therapy for malnourished patients not only does not promote tumor growth, but also enhances patients’ immune function and disease resistance, resulting in greater benefit of anti-tumor therapy. The JCI inspection and evaluation system attaches great importance to the assessment of nutritional status of inpatients and the implementation of nutritional support measures. Nutritional risk is the risk of adverse effects on patient clinical outcomes due to disease, surgery, and nutritional factors, not the risk of malnutrition. Nutritional status assessment aims at early detection of malnutrition and nutritional risk and active nutritional support treatment, which is the crux of the problem and very important. Clinicians, nurses and dietitians conduct nutritional risk screening by asking medical history, weight change, eating and adverse symptoms to determine whether patients have malnutrition and their nutritional status, pay attention to weight loss factors and changes in eating amount in oncology patients, actively search for the causes, formulate reasonable nutritional diets and carry out nutritional support treatment for different situations. Clinically used nutritional preparations and principles of use Clinically used nutritional support measures are: enteral nutrition (EN) and parenteral nutrition (PN); therefore, there are three types of nutritional preparations: oral nutritional preparations, artificial enteral preparations or parenteral nutritional preparations. Enteral nutrition (EN) refers to nutrients given through the gastrointestinal tract, and is divided into large polymer (whole protein) type and small polymer (amino acid, short peptide) type according to different composition. Parenteral nutrition (PN) is the provision of nutrients including amino acids, fats, sugars, vitamins and minerals via intravenous for patients who cannot take in and utilize nutrients via the gastrointestinal tract, in order to inhibit catabolism, promote anabolism and maintain structural protein function. Principles of nutritional support use: According to ASPEN (American Society for Parenteral Nutrition) guidelines, oncology patients follow the principles of nutritional support for general or critically ill patients, i.e. EN is preferred when the gastrointestinal tract is functional and PN is used when the gastrointestinal tract is dysfunctional or impaired. infusion of parenteral nutrition: ESPEN (European Society for Parenteral Nutrition) guidelines recommend infusion of all-in-one nutrient solution, and the required nutrients The required nutrients can be mixed and uniformly administered into the body at the same time to facilitate better metabolism. Because hypertonic glucose and fat emulsion are uniformly diluted, adverse reactions and complications that may occur during separate infusions can be reduced or avoided; the specially designed infusion bag maintains a completely closed and independent system, reducing the chance of contamination. The “one bag per day” delivery method avoids the chance of contamination of the nutrition solution and is very easy to use. Nutritional support treatment for chemotherapy and radiotherapy patients Nutritional support treatment for chemotherapy patients: Tumor chemotherapy drugs interfere with normal cell metabolism, DNA synthesis and replication, resulting in abnormal nutritional metabolism; damage to the mucous membrane of the digestive tract affects the patient’s feeding process and decreases the absorption function, resulting in malnutrition. In addition to the abnormal tumor metabolism, malnutrition is aggravated in patients. ASPEN guidelines state that well-nourished chemotherapy patients do not require routine prophylactic parenteral and enteral nutritional support, as neither PN nor EN support has been shown to be more effective than encouraging oral feeding. Nutritional support therapy is limited to patients with malnutrition, chronic inability to eat, or inadequate nutrient absorption, and should be given in a timely manner when administering anticancer therapy. Nutritional support therapy can be considered when a chemotherapy patient’s daily energy intake is less than 60% of daily energy expenditure for more than 10 days, or when the patient is expected to be unable to eat for 7 or more days, or when the patient has lost weight. Nutritional support treatment for radiotherapy patients: Head and neck tumor radiotherapy can cause loss of appetite or difficulty in eating secondary to oropharyngeal mucous membrane damage, pain, nausea and vomiting; early stage of abdominal radiotherapy can cause nausea, vomiting and diarrhea due to radioactive damage of gastrointestinal mucous membrane, and late stage can cause serious gastrointestinal reactions such as gastrointestinal stenosis and intestinal fistula, which can cause insufficient nutritional intake or absorption disorders for tumor patients in both early and late stage. Inadequate nutritional intake or impaired absorption. Obviously, malnutrition will affect the treatment tolerance of patients, thus affecting the efficacy of radiotherapy treatment and the quality of life of patients. Nutritional support therapy for radiotherapy patients is based on feeding and enteral nutrition. Clinical oncology and nutrition experts do not recommend the routine use of parenteral nutrition for radiotherapy patients without nutritional deficiencies or nutritional risks, but only for patients who cannot tolerate enteral nutrition and need nutritional therapy, such as patients with severe mucositis and severe radiation enteritis after radiotherapy. Nutritional support therapy for patients with end-stage tumors Patients with end-stage tumors are often accompanied by more severe cachexia and are no longer suitable for anti-tumor therapy, and generally have an expected survival of less than 3 months. When approaching the end of life and multiple organ failure, excessive nutritional therapy will increase the metabolic burden of the organism and affect the quality of life. Physicians should carefully evaluate the risk-benefit ratio of nutritional therapy for patients, grasp the indications for nutritional therapy, and decide whether to implement nutritional therapy while respecting the patient’s wishes. The ASPEN guidelines state that nutritional support is rarely used in palliative support for end-stage oncology patients, and if applied, it is likely to benefit a minority of patients. Nutritional support therapy is indicated for patients with end-stage cancer who have an expected survival of more than 40–60 days, a Karlsberg Quality of Life Score (KPS) >50, and no severe organ dysfunction.