Malnutrition has been increasingly recognized as an important factor that can influence the prognosis of patients with chronic liver disease, especially end-stage liver disease. Nutritional status has been used as one of the prognostic criteria for assessing end-stage liver disease in the early Child-Turcotte classification. Unfortunately, nutritional status is not included in the Child-Pugh classification and the MELD score, which are recognized both at home and abroad for assessing the clinical status and severity of patients with cirrhosis and end-stage liver disease. Nutritional status should be emphasized by clinicians along with other complications such as ascites and hepatic encephalopathy. This article summarizes the nutritional metabolic status and nutritional interventions in patients with liver disease. The characteristics of nutritional metabolism in acute hepatitis are less reported at home and abroad. Before the onset of acute hepatitis, the body is in a normal state, and the acute course of the disease will not have too much impact on the nutritional status. Literature reported that the average resting energy expenditure (REE) of patients with acute hepatitis was (27.34±5.46) kcal/(kg?d), which accounted for 117.8% of the normal expected value, of which 85% of the patients were in high metabolic state and 15% were in normal metabolic state. In terms of the oxidation rate of the three major nutrients, carbohydrate was the main energy-supplying substance, and the oxidation rate of carbohydrate was 63.15%; followed by fat, with an oxidation rate of 24.01%; and protein, with an oxidation rate of 13.48%. If the patient’s condition improves in a short period of time, his/her high metabolic state will recover quickly and the oxidation rate of the three major nutrients will not change significantly; if the patient’s condition continues to be unhealed or progressively aggravated or worsened, the high metabolic state will persist. Most of the patients with acute hepatitis are in high metabolic state, and the nutrient supply should meet the increased energy metabolic demand of the patients on the one hand, and prevent the metabolism and function of organs from being affected due to insufficient nutrient substrate; on the other hand, it is also necessary to avoid the excessive nutrient supply from aggravating the damages to the structure and function of the organs. The purpose of nutritional intervention is not only to satisfy the increased demand for energy, protein, electrolytes, trace elements and vitamins in the metabolic process of the patients and prevent or correct the existing malnutrition, but also to maintain or enhance the immunity of the patients and the defense mechanism against infections, and to promote the repair of liver tissue. Second, chronic hepatitis, foreign research on nutritional metabolism of chronic hepatitis mainly focuses on chronic hepatitis C. Literature reports that the incidence of diabetes mellitus in patients with hepatitis C virus (HCV) infection is 21%, and the incidence of diabetes mellitus in patients with hepatitis B virus (HBV) infection is 12%. HCV infection is also significantly correlated with lipid metabolism, which can be interfered with by interaction with apolipoproteins. In patients with chronic hepatitis, liver function is basically normal during the stabilization period, and nutritional status and indices of energy metabolism are generally within the normal range. One study analyzed 142 cases of chronic hepatitis B patients with subjective nutritional evaluation method, and the incidence of malnutrition was 14.10%; 15.49% of the patients were in high metabolic state, 47.18% were in normal metabolic state, and 37.32% were in low metabolic state. The average respiratory quotient (RQ) was 0.84±0.06, which was in the normal range, and the three major nutrients were mainly carbohydrates, and the oxidation rates of carbohydrates, fats, and proteins were 45.62%, 26.33%, and 27.99%, respectively. Most of the patients with chronic hepatitis had no significant difference in nutritional metabolic status with healthy people, and could eat normally without artificial nutritional support. In patients with chronic hepatitis, the diet should be adequate in protein, high in vitamins and moderate in fat while ensuring sufficient calories. Supplementation of trace elements is also very necessary, such as selenium supplementation can help antioxidant, also has a certain preventive effect on the occurrence of tumors. Cirrhosis Protein-energy malnutrition is the most common form of malnutrition in patients with cirrhosis, 80% of patients with cirrhosis have been found to be malnourished, and even in patients with Child-Pugh class A, the malnutrition rate is as high as 25%. The morbidity and mortality rates of malnourished patients are quite high. Early nutritional intervention can prolong the life span, improve the quality of life, minimize complications and increase the success rate of liver transplantation. The metabolic characteristics of cirrhotic patients are mainly abnormal protein and energy metabolism. Some scholars believe that abnormal metabolism of 3 major nutrients is an independent prognostic factor for cirrhotic patients. Overseas studies have shown that hypermetabolism is the most common metabolic characteristic of cirrhotic patients, but not all cirrhotic patients have hypermetabolic state. The reports on the total energy consumption of cirrhotic patients vary. Some reports show that 58% of cirrhotic patients have basically normal energy metabolism, and 12% have low energy metabolism; others report that cirrhotic patients have high energy metabolism and high fat oxidation rate. Patients with high energy metabolism often suffer from weight loss. Reduced intake and increased energy consumption can lead to negative energy balance, which is more likely to lead to malnutrition and increase the morbidity and mortality rate. In cirrhotic patients, RQ values are significantly lower than in healthy subjects, as evidenced by a marked increase in fat oxidation and a marked decrease in carbohydrate oxidation. This change in energy metabolism is similar to starvation and may lead to malnutrition. After nighttime energy supplementation, the RQ, carbohydrate and fat oxidation rates of cirrhotic patients recovered significantly and eventually approached normal levels. In order to ensure a smooth caloric supply, improve nutritional status and reduce complications, both the American Society for Parenteral Nutrition (ASPEN) and the European Society for Parenteral Nutrition (ESPEN) recommend that cirrhotic patients change their dietary intake pattern by eating fewer and more frequent meals, 4-6 meals per day, including late evening snack (LES). LES means that if the total amount of daily food remains unchanged, part of the food should be eaten before bedtime without increasing the total energy intake. A number of foreign scholars have studied the intervention of LES in patients with cirrhosis of different etiologies, and the types of additional meals were 200 kcal of carbohydrates or 210 kcal of compound preparation rich in branched-chain amino acids, and the duration of the intervention ranged from 2 weeks to 3 months. The results showed that the patients’ RQ and carbohydrate oxidation rate increased significantly, fat oxidation rate and protein oxidation rate decreased, and the metabolic status of the body was improved, and the lower the baseline RQ value, the more obvious the improvement of metabolic status. There are fewer intervention studies on the metabolism of chronic liver disease in China. In one study, LES (about 200 kcal of carbohydrate) was administered to 8 patients with chronic plus acute liver failure, and it was found that LES could improve the morning RQ, increase the proportion of carbohydrate energy supply, save fat and protein, and rationalize the proportion of oxidized energy supply of the 3 major nutrients. The Critical Care Medicine Branch of Chinese Medical Association recommends that the energy supply of patients with compensated cirrhosis should be calculated as 25~35 kcal/(kg?d), which can be increased in the case of combined malnutrition and reduced in the case of hepatic encephalopathy.ESPEN parenteral nutrition guideline recommends that: when the fasting time is 72 h or enteral nutrition can not be carried out, patients with cirrhosis should be provided with parenteral nutritional support, and the Subjective Globally Appraisal (SGA) method or anthropometric method should be adopted to evaluate the malnutrition. When fasting for 72 h or when enteral nutrition cannot be performed, parenteral nutritional support should be given to patients with cirrhosis, and the risk of malnutrition should be assessed using the subjective global assessment (SGA) or anthropometric methods, with a total energy intake of 1.3 × REE, glucose of 2-3 g/(kg?d), and glucose providing 50% to 60% of nonprotein calories. Glucose infusion should be used in conjunction with insulin, and water-soluble vitamins and trace elements should be given at the same time. Amino acid intake of cirrhotic patients should be 1.2~1.5 g/(kg?d). IV. Liver failure Patients with liver failure are in a state of stress and high metabolism, the measured REE value is high, and the oxidized substrate is mainly fat.Schneeweiss et al. found that the energy metabolism of 12 patients with acute liver failure was significantly higher than that of healthy people by about 30% through metabolic measurements.Walsh et al. found that the energy consumption of 16 patients with acetaminophen-induced acute liver failure. In a study of 16 patients with acetaminophen-induced acute hepatic failure, Walsh et al. found that energy expenditure was significantly increased by approximately 18% despite the presence of extensive hepatocellular necrosis, which may be related to the systemic inflammatory response that accompanies hepatic failure. This may be related to the systemic inflammatory response that accompanies liver failure. However, not all critically ill patients show a typical hypermetabolic response, and in one study, using the ratio of measured REE to the energy expenditure predicted by the H-B formula to evaluate the degree of metabolism, only 35-62% of critically ill patients were hypermetabolic, whereas 15%-20% of patients were actually hypometabolic. The pros and cons of hypometabolism are inconclusive. Fan Chunlei et al. found that patients with chronic severe hepatitis had low REE, low metabolic state, impaired glucose metabolism, and could only enhance fat mobilization for energy supply. With the recovery of liver function, the utilization of glucose in patients increased, and the increase of RQ value could be a sign of recovery. Some scholars found that most of the chronic severe hepatitis are in low metabolic state, and the decrease of energy consumption can help to maintain the balance between intake and consumption and reduce the energy imbalance, and this low metabolic state may be a protective mechanism for the body. Feng Yanmei et al. found that patients with chronic severe hepatitis fasted at night, and the RQ value was the lowest in the whole day when fasting in the morning, and fat and protein were the main energy-supplying substances, and the RQ value could be increased rapidly after the intravenous application of glucose. In 2006, the Chinese version of “Liver Failure Diagnostic and Treatment Guidelines” recommended that nutritional support for patients with liver failure should be based on a diet high in carbohydrates, low in fat, and moderate in protein; for those who have not eaten enough, adequate fluids and vitamins should be given intravenously daily to ensure that the total calories in the daily diet are more than 6,272 kJ (1,500 kcal).In 2009, the ESPEN guidelines recommended that the nutritional intervention strategy in patients with acute liver failure is similar to that in patients with liver cirrhosis. The 2009 ESPEN Parenteral Nutrition Guidelines recommend the same nutritional intervention strategies for patients with acute liver failure as for patients with cirrhosis. Amino acid intake in patients with acute hepatic failure should be 0.8-1.5 g/(kg?d), with the addition of 0.8-1.2 g/(kg?d) of fat to reduce insulin resistance. In the case of third or fourth degree hepatic encephalopathy, parenteral nutritional preparations rich in branched-chain amino acids should be supplemented, and changes in blood glucose, blood lipids, electrolytes, and blood ammonia should be monitored, so as to adjust the treatment program at any time. V. Prospect The study of nutritional support for chronic liver disease is still in the initial stage, and there are still many issues to be explored, such as the widespread application of nutritional risk assessment (NRS-2002), and the nutritional metabolism of liver disease complicating other diseases such as diabetes mellitus and hypertension. In addition, there is a lack of guidelines on nutritional support for patients with chronic liver disease in China, and the intake and mode of nutritional intervention need to be further studied. One of the significance of emphasizing the nutritional metabolism of patients with various acute and chronic liver diseases is that the concept and method of nutritional support can be introduced into the family life of patients, so as to achieve the goal of improving the quality of life and prolonging life.