Nutritional support is one of the major advances in contemporary surgery and surgeons are pioneers in clinical nutrition. We have believed since the end of the last century that nutritional support has an important place in the treatment of patients with hepatobiliary injuries and has a significant role in improving patient outcomes. Professor Dudrick further pointed out a decade ago that the main purpose of nutritional support in hepatobiliary surgery patients is not only to provide nutritional substrates to facilitate tissue repair, but also to maintain hepatocyte regeneration and function, and to improve immune imbalance and reduce complications. However, there is not yet a nutritional formula that can fully adapt to various hepatobiliary surgical diseases, which also indicates that nutritional support for hepatobiliary surgery patients still faces great laboratory and clinical challenges. 1, hepatobiliary surgery patient nutrition support status is not optimistic malnutrition and the prognosis of surgical patients as early as 1936 has been recognized, Studley et al. found that malnutrition of ulcer patients with surgical mortality is nearly 10 times the normal nutrition. 75 years have passed, although anesthesia and surgical techniques have made great progress, especially in the last 20 years, hepatobiliary surgery technology is a breakthrough progress. A study published in Ann Surg in 2010 concluded that preoperative serum albumin levels were an independent risk factor for gastrointestinal surgical site infection (SSI), again reminding us of the importance of surgical nutrition. The liver is the central organ of human metabolism, with multiple functions such as synthesis, storage, decomposition, excretion, detoxification and secretion. The biliary tract is the outflow tract of liver secretion, and bile and pancreatic juice play an important role in the digestion and absorption of food. Because of the importance of the hepatobiliary system in nutrient absorption and metabolism, hepatobiliary surgery patients, especially those with hepatobiliary tumors, have different degrees of bile salt synthesis and enterohepatic circulation disorders, which directly affect nutrient absorption and lead to different degrees of malnutrition, and it is essential to conduct necessary nutritional assessment and necessary supportive treatment for hepatobiliary surgery patients. Since the common indicators of nutritional assessment are often changed due to hepatobiliary pathologies, the nutritional assessment of such patients is more likely to be neglected by surgeons, in fact, the incidence of malnutrition in hospitalized patients may exceed 50%, and in patients undergoing major abdominal surgery is as high as 65%. As one of the important advances in contemporary surgery, nutritional support has played an important role in improving surgical success, patient prognosis and quality of life, but the emphasis of hepatobiliary surgeons on clinical nutritional risk screening and nutritional support is still not optimistic. One author observed changes in the perioperative nutritional status of 26 pancreaticoduodenectomy patients and found that patients’ nutritional status continued to decline up to 3 months after surgery, even with postoperative nutritional support. And a joint survey of 31 pancreatic centers within the United Kingdom noted that although most surgical specialists have recognized the impact of malnutrition on postoperative risk after pancreaticoduodenectomy, only 18% of medical centers routinely perform preoperative nutritional risk screening, and even fewer than 13% have nutritional formulas specifically for hepatobiliary surgical disease. Most surgeons do not routinely perform risk screening and nutritional support according to evidence-based guidelines, and some authors have pessimistically concluded that “perioperative nutritional support remains a surgical orphan”. In recent years, there has been a growing number of guidelines on nutritional support, and both the European Society for Parenteral Enteral Nutrition (ESPEN) and the American Society for Parenteral Enteral Nutrition (ASPEN) have developed clinical guidelines on nutritional support for patients in hepatobiliary surgery, each with their own specific descriptions. The original purpose of the guidelines is to help clinicians develop systematic, evidence-based clinical treatment plans, but clinicians still face great challenges in translating the recommendations in the guidelines into concrete applications in clinical practice and in interpreting the different levels of recommendations in the guidelines. The survey found that 50% of surgical critical care patients did not receive the standard treatment as recommended by the guidelines. In other words, it is more important to interpret the guidelines correctly than to implement nutrition support in accordance with the recommendations of the guidelines. Poor nutrition is likely to increase the rate of postoperative complications, such as incisional dehiscence, poor tissue healing, infection, delayed gastric emptying, slow recovery, etc. Low preoperative albumin levels can lead to increased postoperative complications and mortality. The body is in a highly stressful state after complex hepatobiliary surgery, which is characterized by high catabolism and concurrent impaired utilization of exogenous amino acids and energy, the latter of which further aggravates the difficulty of postoperative nutritional support for hepatobiliary surgery patients. It is no longer possible to compare the prognosis of hepatobiliary surgery patients with or without perioperative nutritional support, which is the basic consensus. The previous belief that preoperative nutritional support is not relevant to postoperative complication rates and mortality may be related to inappropriate access or insufficient duration of nutritional support. Although there is no consensus on the duration of preoperative nutritional support, the general recommendation is 7-14 days, which is too short for nutritional support to be effective. In the early postoperative period, the main focus is to maintain internal homeostasis and reduce surgical stress, so postoperative nutritional support can be started at 48 h after surgery. Postoperative hepatobiliary nutritional support is mainly used for those who had malnutrition before surgery and failed to correct it effectively, as well as for those who have postoperative complications, such as intestinal fistula, pancreatic fistula, biliary fistula, and severe abdominal infection, etc. Postoperative radiotherapy causing nausea and vomiting that prevent patients from eating is also an indication for nutritional support. As for the mode of nutritional support, enteral nutrition has been clearly recommended, which not only can maintain the intestinal mucosal barrier, stimulate the secretion of gastrointestinal fluid and gastrointestinal hormones, improve portal perfusion, maintain hepatobiliary function and reduce stress, but also can be implemented when necessary, to improve enteral nutrition tolerance and promote nutrient absorption. Therefore, during complex hepatobiliary surgery, prophylactic jejunostomy can be performed intraoperatively in consideration of those who are at high risk for postoperative gastrointestinal complications. It is worth noting that the emphasis on enteral nutrition is not a complete abandonment of parenteral nutrition, which can be used as a supplement to the former. The ESPEN guidelines suggest that parenteral nutrition should be supplemented once more than 60% of energy requirements cannot be met by enteral nutrition. As the concept of accelerated rehabilitation surgery (FTS) has advanced in recent years, more and more evidence-based medical studies have shown that the core of FTS is to reduce surgical stress. FTS not only does not ignore the importance of nutritional support, but also emphasizes the important role of nutritional support for perioperative recovery. From a nutritional perspective, its main goals are to optimize nutritional support and to avoid preoperative starvation in order to minimize negative nitrogen balance. While the traditional practice of fasting the night before elective surgery not only induces metabolic stress and impairs mitochondrial function but also produces insulin resistance, preoperative intestinal carbohydrate loading reduces postoperative insulin resistance, improves nitrogen balance, shortens postoperative hospital days, and facilitates postoperative recovery. A recent study showed that 145 patients who underwent pancreatic resection had significantly fewer complications and shorter hospital days after implementing the accelerated recovery surgical concept. The advances in minimally invasive surgical techniques, especially in hepatobiliary surgery, which is mainly confined to the right upper abdomen and causes relatively little harassment to the gastrointestinal tract, make early postoperative enteral or oral nutrition more possible. Surgical trauma can reduce insulin sensitivity and the ability of tissues to take up sugar and glycogen, leading to hyperglycemia, and the impact of hyperglycemia on surgical prognosis should be particularly noted when implementing nutritional support. Glycemic control and intensive insulin therapy in critically ill patients has been widely emphasized and should be so in the perioperative period. The complication rate increases nearly threefold in those with early hyperglycemia (>7.77 mmo/L) after pancreaticoduodenectomy, and strict postoperative glycemic control can reduce the rate of postoperative complications. Although hepatobiliary surgery has not been reported, perioperative blood glucose control of 7.77-9.99 mmol/L is a more ideal range. 3. Hepatectomy and nutritional support Hepatectomy has gained a breakthrough in the past 20 years, with a significantly higher surgical success rate and a significantly lower complication rate, related not only to the in-depth understanding of liver anatomy and major advances in hepatectomy techniques, but also to the advances in preoperative nutritional assessment and postoperative nutritional support. In addition, the success of hepatectomy is closely related to postoperative recovery and regeneration of residual liver function; therefore, preoperative nutritional status is also one of the important risk factors for postoperative residual liver regeneration, further emphasizing the importance of preoperative nutritional assessment. Nutritional support is one of the standard therapeutic measures for regeneration of the residual liver after major hepatectomy. Carbohydrates are the main source of energy, and recent experiments have shown that increasing preoperative liver glycogen reserves significantly improves the liver’s tolerance to oxidative stress and ischemia-reperfusion injury, and that preoperative sugar intake can prevent or reduce liver dysfunction after major hepatectomy. However, there is a lack of systematic risk factor analysis on the nutritional status of the liver in hepatectomized patients and their postoperative liver regeneration capacity. Some experiments have shown that age, gender, body mass index, primary liver disease, chemotherapy, platelet count, and degree of liver lipidation may affect postoperative liver regeneration. The preoperative nutritional status of the liver directly determines the postoperative residual liver regeneration capacity, and therefore the nutritional support regimen for hepatectomy varies in livers with different nutritional status. For patients with healthy livers undergoing major hepatectomy, preoperative malnutrition is mainly related to postoperative complications, and the main purpose of nutritional support is to supply nutritional substrate early after surgery, with enteral nutrition preferred, and parenteral nutrition is only suitable for patients who cannot consume energy via the intestine or oral cavity for 7-10 days; for patients with living donor liver or laparoscopic hepatectomy, the nutritional status is relatively good, and the postoperative period can be accelerated according to The most challenging aspect is the nutritional support for patients with liver resection in combination with cirrhosis, where the mode and formulation of nutritional support is still controversial. There is no perfect nutritional formula that can be applied to all patients with all types of hepatobiliary surgical diseases. In the near future, individualized nutrition support guidelines for different liver dysfunctions, such as fulminant liver failure, cholestatic liver disease, fatty liver, and cirrhosis, may be available. 4. Metabolic and immune support – the frontier of nutritional therapy In the last 30 years, the concepts and principles of surgical nutrition have advanced considerably, and the understanding of the molecular and biological effects of nutrients in maintaining homeostatic balance in the organism has improved in depth. Early nutritional support mostly focused on providing substrates to facilitate the body to maintain lean body mass, immune function and prevent metabolic complications. Nowadays, nutritional support focuses more on nutritional therapy, especially on blocking the metabolic response to stress, preventing oxidative damage to cells and regulating immune function, and the fastest progress is now on various special nutritional substrates and fine glycemic control. A large number of studies have demonstrated that parenteral nutrition can affect liver immune function, and the latest study found that parenteral nutrition enhanced with fish oil can partially reverse PN-induced immune destruction and improve PN-induced liver function impairment after intra-portal injection of bacteria into a rat model of liver function impairment; intestinal supplementation with glycyl-glutamine dipeptide can protect intestinal mucosal barrier function in liver transplant rats; studies found that inflammation , infection and oxidative stress can exacerbate the neurological damage caused by blood ammonia, and recent studies have attempted to prevent or mitigate hepatic encephalopathy through supplementation with certain antioxidants; there is much controversy about branched-chain amino acids (BCAAs), and there has been a lack of convincing data, especially with parenteral administration. Recent studies have found that enteral BCAA supplementation improves serum erythropoietin (EPO) levels after hepatectomy, which in turn may be beneficial for hepatocyte protection. This new field of nutritional therapy is often referred to as nutritional immunology or pharmacological immunology. In recent years there has been a growing literature on nutritional immunology, all agreeing that perioperative immunonutrition improves the prognosis of surgical patients, but questions remain: the optimal timing of immunonutrition? The choice of specific nutritional substrates? What are the doses? More research is still needed to explore. Although the development of hepatobiliary surgery is changing rapidly and the concept and practice of clinical nutritional support has progressed greatly, there are still many aspects of specific practice and theoretical research that need to be improved. The purpose of nutritional support is not only to provide nutritional substrates, but also to improve patient prognosis by adding specific nutritional substrates. Through reasonable perioperative nutritional support treatment, regulating body immunity, regulating blood glucose, maintaining tissue and organ function, and thus improving surgical outcomes, is the direction that hepatobiliary surgery nutritional support needs to strive for in the future.