The most basic biochemical characteristics of tumor cells are malignant proliferation, poor differentiation, invasion of surrounding tissues and metastasis, and all malignant manifestations of tumor cells have certain biochemical processes as the base cancer. The abnormalities of carbohydrate, fat and protein metabolism will eventually lead to malnutrition. 1.Abnormal energy metabolism Increased energy consumption and ineffective energy utilization can often lead to malnutrition in tumor hosts. In normal people, the rate of basal cancer metabolism decreases when food intake is reduced, while cancer patients lack the response of reduced basal cancer metabolism when food intake is reduced. Resting metabolism is higher in cancer patients, and an increase in resting metabolic rate parallels disease progression and reduces nutrient intake [l]. Shaw et al. concluded that alterations in metabolic rate may depend on the type of tumor. Patients with lower gastrointestinal tumors tend to have normal metabolism, while patients with upper gastrointestinal tumors have increased metabolic rates. 2. Abnormal glucose metabolism Rapidly growing cancer tissues exhibit increased glycolysis even under aerobic conditions. The phenomenon of aerobic oxidation inhibiting enzymes in normal tissues is weakened or disappeared, and replaced by enzymes inhibiting oxidation. Therefore, the energy required for tumor cell anabolism comes to a large extent from glycolysis. In general, the normal liver is supplied with about 99% of energy by glycolytic oxidation and 1% by enzymatic energy. Cancer patients cannot tolerate glucose after oral or intravenous administration and produce hyperglycemia, and the clearance of glucose is delayed, which may be partly due to the decreased sensitivity of peripheral tissues to insulin, or may be due to the weakened response of insulin to sugar secretion. 3. Abnormal lipid metabolism Changes in lipid metabolism in cancer patients include decreased fat storage and increased fat mobilization, with overall fat reduction being common, along with increased fatty acid oxidation. The clearance rate of endogenous stored fat and exogenous ingested fat increases in cancer patients in fasting and ingestion states. glucose intake also fails to inhibit lipolysis, and fatty acid oxidation continues. wilson et al. measured the fat clearance rate in patients with colon and rectal cancer and the effect of surgery and TPN on the clearance rate, and found that the fat clearance rate increased in most cancer patients. When re-measured 12 weeks after radical surgery, the fat clearance rate of most patients was close to normal, and the fat clearance rate decreased in patients who received TPN. 4. Abnormal protein metabolism Corresponding to the vigorous growth of tumor tissue is the increase of protein anabolism and the weakening of amino acid catabolism. Egbert et al. used L-[I-13C]-labeled leucine leucine as a tracer to study the metabolism of egg/leucine in 15 resectable colon cancer tumors. Protein metabolism in peripheral tissues and the exchange rate of 20 amino acids between tumors and peripheral tissues were also measured, and in tumors, essential and branched-chain amino acid uptake was elevated. Tracer analysis showed net protein retention in tumors and peripheral protein loss. Grouping tumors by histology revealed significant differences in the retention of 10 amino acids, including leucine, with increased net retention in tumors with poor prognosis, possibly due to increased amino acid requirements as a result of rapid tumor growth.Tayek et al. conducted a study using rats with sibling sarcoma or liver cancer to compare host muscle protein synthesis and degradation rates.At day 18 after tumor implantation, muscle protein synthesis decreased in rats, but liver protein synthesis increased, as well as a net increase in overall protein synthesis. This metabolism can lead to malnutrition in the organism.