AbstractNutrition plays important roles in recovery after gastroenterological surgery. Severe surgical stress increases muscle breakdown and lipolysis, thereby accelerating wound healing and enhancing host defense against microbes. Malnourished patients have insufficient amounts of muscle and body fat. Therefore, they may not appropriately respond to surgical stress. Perioperative nutritional therapy maintaining nutritional status reduces postoperative complications and accelerates recovery after surgery, particularly for malnourished patients. In addition, perioperative oral or enteral nutrition is now recommended for preserving host defense mechanisms against microbes. Lack of enteral nutrition impairs gut and hepatic immunity, systemic mucosal defense and peritoneal host defense, even when nutrient amounts supplied by parenteral nutrition are adequate. Thus, surgeons should avoid no oral or enteral nutrition periods. Supplemental administration of specific nutrients such as glutamine, arginine and ω‐3 fatty acids is termed “immunonutrition”, and is expected to reduce the morbidity of infectious complications and length of hospital stay. Nutritional therapy is important even after discharge to maintain body weight and compensate for abnormalities in the digestion and absorption of nutrients. Understanding the significance of nutrition in gastroenterological patients leads to better outcomes.