Preoperative nutrition therapy in people undergoing gastrointestinal surgery

Background Poor preoperative nutritional status has been consistently linked to an increase in postoperative complications and worse surgical outcomes. We updated a review first published in 2012. Objectives To assess the effects of preoperative nutritional therapy compared to usual care in people undergoing gastrointestinal surgery. Search methods We searched the Cochrane Central Register of Controlled Trials, MEDLINE, Embase, three other databases and two trial registries on 28 March 2023. We searched reference lists of included studies. Selection criteria We included randomised controlled trials (RCTs) of people undergoing gastrointestinal surgery and receiving preoperative nutritional therapy, including parenteral nutrition, enteral nutrition or oral nutrition supplements, compared to usual care. We only included nutritional therapy that contained macronutrients (protein, carbohydrate and fat) and micronutrients, and excluded studies that evaluated single nutrients. We included studies regardless of the nutritional status of participants, that is, well‐nourished participants, participants at risk of malnutrition, or mixed populations. We excluded studies in people undergoing pancreatic and liver surgery. Our primary outcomes were non‐infectious complications, infectious complications and length of hospital stay. Our secondary outcomes were nutritional aspects, quality of life, change in macronutrient intake, biochemical parameters, 30‐day perioperative mortality and adverse effects. Data collection and analysis We used standard Cochrane methodology. We assessed risk of bias using the RoB 1 tool and applied the GRADE criteria to assess the certainty of evidence. Main results We included 16 RCTs reporting 19 comparisons (2164 participants). Seven studies were new for this update. Participants' ages ranged from 21 to 79 years, and 62% were men. Three RCTs used parenteral nutrition, two used enteral nutrition, eight used immune‐enhancing nutrition and six used standard oral nutrition supplements. All studies included mixed groups of well‐nourished and malnourished participants; they used different methods to identify malnutrition and reported this in different ways. Not all the included studies were conducted within an Enhanced Recovery After Surgery (ERAS) programme, which is now current clinical practice in most hospitals undertaking GI surgery. We were concerned about risk of bias in all the studies and 14 studies were at high risk of bias due to lack o