• Anne Marie Sowerbutts, Sorrel Burden, Jana Sremanakova, Chloe French, Stephen R Knight, and Ewen M Harrison.
• School of Health Sciences, The University of Manchester, and Manchester Academic Health Science Centre, Manchester, UK.
• Cochrane Db Syst Rev. 2024 Apr 8; 4 (4): CD008879CD008879.

BackgroundPoor 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.ObjectivesTo assess the effects of preoperative nutritional therapy compared to usual care in people undergoing gastrointestinal surgery.Search MethodsWe 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 CriteriaWe 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 AnalysisWe 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 ResultsWe 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 of blinding. We are uncertain if parenteral nutrition has any effect on the number of participants who had a non-infectious complication (risk ratio (RR) 0.61, 95% confidence interval (CI) 0.36 to 1.02; 3 RCTs, 260 participants; very low-certainty evidence); infectious complication (RR 0.98, 95% CI 0.53 to 1.80; 3 RCTs, 260 participants; very low-certainty evidence) or length of hospital stay (mean difference (MD) 5.49 days, 95% CI 0.02 to 10.96; 2 RCTs, 135 participants; very low-certainty evidence). None of the enteral nutrition studies reported non-infectious complications as an outcome. The evidence is very uncertain about the effect of enteral nutrition on the number of participants with infectious complications after surgery (RR 0.90, 95% CI 0.59 to 1.38; 2 RCTs, 126 participants; very low-certainty evidence) or length of hospital stay (MD 5.10 days, 95% CI -1.03 to 11.23; 2 RCTs, 126 participants; very low-certainty evidence). Immune-enhancing nutrition compared to controls may result in little to no effect on the number of participants experiencing a non-infectious complication (RR 0.79, 95% CI 0.62 to 1.00; 8 RCTs, 1020 participants; low-certainty evidence), infectious complications (RR 0.74, 95% CI 0.53 to 1.04; 7 RCTs, 925 participants; low-certainty evidence) or length of hospital stay (MD -1.22 days, 95% CI -2.80 to 0.35; 6 RCTs, 688 participants; low-certainty evidence). Standard oral nutrition supplements may result in little to no effect on number of participants with a non-infectious complication (RR 0.90, 95% CI 0.67 to 1.20; 5 RCTs, 473 participants; low-certainty evidence) or the length of hospital stay (MD -0.65 days, 95% CI -2.33 to 1.03; 3 RCTs, 299 participants; low-certainty evidence). The evidence is very uncertain about the effect of oral nutrition supplements on the number of participants with an infectious complication (RR 0.88, 95% CI 0.60 to 1.27; 5 RCTs, 473 participants; very low-certainty evidence). Sensitivity analysis based on malnourished and weight-losing participants found oral nutrition supplements may result in a slight reduction in infections (RR 0.58, 95% CI 0.40 to 0.85; 2 RCTs, 184 participants). Studies reported some secondary outcomes, but not consistently. Complications associated with central venous catheters occurred in RCTs involving parenteral nutrition. Adverse events in the enteral nutrition, immune-enhancing nutrition and standard oral nutrition supplements RCTs included nausea, vomiting, diarrhoea and abdominal pain.Authors' ConclusionsWe were unable to determine if parenteral nutrition, enteral nutrition, immune-enhancing nutrition or standard oral nutrition supplements have any effect on the clinical outcomes due to very low-certainty evidence. There is some evidence that standard oral nutrition supplements may have no effect on complications. Sensitivity analysis showed standard oral nutrition supplements probably reduced infections in weight-losing or malnourished participants. Further high-quality multicentre research considering the ERAS programme is required and further research in low- and middle-income countries is needed.Copyright © 2024 The Cochrane Collaboration. Published by John Wiley & Sons, Ltd.

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