After the appearance of malignant tumors in the human body, the metabolism of the organism undergoes a series of changes, which are manifested in different metabolic states of the three major nutrients, namely, carbohydrates, fats and proteins, in the tumor tissues and in the host. The main mechanism involves the development of endocrine disorders in the body, manifested by insulin resistance or decreased secretion, elevated corticosteroids and growth hormone. The body develops a chronic inflammatory response with increased secretion of pro-inflammatory factors TNFα, IL-6, IL-1, and IFNγ. Tumor tissue proliferation and metabolic signaling pathway activation, oncogene activation, inactivation of oncogenes, abnormalities of enzymes and transporter carriers. 1.Changes in lipid metabolism In patients, fat mobilization increases, endogenous fat consumption increases, fat reserves decrease and are not inhibited by glucose input; fatty acid oxidative catabolism increases; plasma lipoproteins (CM and VLDL) increase, plasma triglyceride levels increase, and exogenous fat utilization decreases. 2.Changes in carbohydrate metabolism Glucose uptake by tumor tissues is increased, and tumor cells can obtain intermediate metabolites through glycolysis for synthesis of fat, protein and nucleic acid to meet their own active synthesis needs. Due to the changes of fat and carbohydrate metabolism in tumor patients, it is recommended to appropriately increase the ratio of fat energy supply and decrease the ratio of carbohydrate energy supply, and the ratio of lipid-sugar energy supply can be up to 1:1. When the patients are accompanied by hypertriglyceridemia, or when they are accompanied by the symptoms of anorexia nervosa, nausea, diarrhea and so on, the ratio of fat energy supply can be adjusted downward according to the patients’ conditions. When the patient is accompanied by diabetes mellitus, it is necessary to refer to the dietary guidance for diabetes mellitus and the dietary guidance standards for patients with malignant tumors at the same time, so as to keep the patient’s blood glucose normal and stable. Foods from n-3 and n-9 fatty acid sources can be increased appropriately to reduce cancer-related chronic inflammatory responses.