Background and Aims: Immunonutrition can improve the body's nutritional status, regulate the body's immune system, control the excessive inflammatory response in the body, and speed patients' postoperative recovery. However, there is no final conclusion about the influences of preoperative immunonutrition on patients undergoing pancreatoduodenectomy (PD). Therefore, this study systematically evaluated the efficacy of preoperative immunonutrition in patients undergoing PD. 
Methods: The randomized controlled trials (RCTs) concerning PD patients receiving preoperative immunonutrition were collected by a computer-based search in several national and international databases from the time of inception to July 2019. After literature review and screening, data extraction and assessment of risk of bias of the selected studies by two reviewers independently, Meta-analysis was performed by using RevMan 5.3 software.
Results: A total of 11 RCTs were included, involving 614 patients, with 310 in study group (receiving preoperative immunonutrition support) and 304 in control group (receiving conventional nutrition support before operation). The results of the Meta-analysis showed that there were no significant differences in operative time, intraoperative blood loss and number of cases requiring intraoperative blood transfusion between the two groups (all P>0.05); the overall incidence of infective complications in study group was significantly lower than that in control group (OR=0.37, 95% CI=0.23–0.59, P<0.000 1), which was mainly driven by the significantly low incidence of wound infection (OR=0.51, 95% CI=0.29–0.89, P=0.02); in study group versus control group, no significant difference was noted in the overall incidence of non-infective complications (OR=0.89, 95% CI=0.67–1.18, P=0.41) as well as the incidence of each specific non-infective complication (all P>0.05); the length of hospital stay of study group was significantly shorter than that of control group (MD=–1.91, 95% CI=–3.21––0.60, P=0.004).
Conclusion: The current evidence indicates that the preoperative use of immunonutrition in PD patients is beneficial to reduce the occurrence of postoperative infective complications, shorten the length of hospital stay, and promote postoperative recovery. However, due to limitations of number and quality of the included studies, the above conclusions need to be verified by more high-quality studies.