Immunomodulating versus high-protein oral preoperative supplement in surgical patients – A two-center, prospective, randomized clinical trial

•Between January 2011 and December 2020, 299 well-nourished patients undergoing major abdominal surgery were randomized to receive either a preoperative immunomodulating or high-protein oral diet for 7 d after surgery•Both groups were comparable in terms of age, sex, and type of surgery•Median postoperative hospital stay, postoperative complications, and risk of readmission were similar•No difference between immunomodulating and high-protein preoperative diets in surgical patients were demonstrated, contradicting earlier research