Post-operative management in gastrointestinal (GI) surgery is becoming well established with 'Enhanced Recovery After Surgery' protocols starting 24 hours prior to surgery with carbohydrate loading and early oral or enteral feeding given to patients the first day following surgery. However, whether or not nutritional intervention should be initiated earlier in the preoperative period remains unclear. Poor pre-operative nutritional status has been linked consistently to an increase in post-operative complications and poorer surgical outcome. To review the literature on preoperative nutritional support in patients undergoing gastrointestinal surgery (GI). The searches were initially run in March 2011 and subsequently updated in February 2012. Databases including all EBM Reviews (Cochrane DSR, ACP Journal Club, DARE, CCTR, CMR, HTA and NHSEED) MEDLINE, EMBASE, AMED, British Nursing Index Archive using OvidSP were included and a search was run on each database separately after which duplicates were excluded. The inclusion criteria were randomised controlled trials that evaluated pre-operative nutritional support in GI surgical participants using a nutritional formula delivered by a parenteral, enteral or oral route. The primary outcomes included post-operative complications and length of hospital stay. Two observers screened the abstracts for inclusion in the review and performed data extraction. Bias was assessed for each of the included studies using the bias assessment tables in the Cochrane Software Review Manager (version 5.1, Cochrane Collaboration). The trials were analysed using risk ratios with Mantel-Haenszel in fixed effects methods displayed with heterogeneity. Meta-analyses were undertaken on trials evaluating immune enhancing (IE) nutrition, standard oral supplements, enteral and parenteral nutrition (PN) which were administered pre-operatively.Study characteristics were summarised in tables. Dichotomous and ratio data were entered into meta-analyses for the primary outcomes. These were then summarised in tables with assumed and corresponding risk with relative effect giving 95% confidence intervals. The searches identified 9900 titles and, after excluding duplicates, 6433 titles were initially screened. After the initial title screen, 6266 were excluded. Abstracts were screened for 167 studies and 33 articles were identified as meeting the inclusion criteria, of which 13 were included in the review after an assessment of the complete manuscripts.Seven trials evaluating IE nutrition were included in the review, of which 6 were combined in a meta-analysis. These studies showed a low to moderate level of heterogeneity and significantly reduced total post-operative complications (risk ratio (RR) 0.67 CI 0.53 to 0.84). Three trials evaluating PN were included in a meta-analysis and a significant reduction in post-operative complications was demonstrated (RR 0.64 95% CI 0.46 to 0.87) with low heterogeneity, in predominantly malnourished participants. Two trials evaluating enteral nutrition (RR 0.79, 95% CI 0.56 to 1.10) and 3 trials evaluating standard oral supplements (RR 1.01 95% CI 0.56 to 1.10) were included, neither of which showed any difference in the primary outcomes. There have been significant benefits demonstrated with pre-operative administration of IE nutrition in some high quality trials. However, bias was identified which may limit the generalizability of these results to all GI surgical candidates and the data needs to be placed in context with other recent innovations in surgical management (eg-ERAS). Some unwanted effects have also been reported with components of IE nutrition in critical care patients and it is unknown whether there would be detrimental effects by administering IE nutrition to patients who could require critical care support after their surgery. The studies evaluating PN demonstrated that the provision of PN to predominantly malnourished surgical candidates reduced post-operative complications; however, these data may not be applicable to current clinical practice, not least because they have involved a high degree of 'hyperalimentation'. Trials evaluating enteral or oral nutrition were inconclusive and further studies are required to select GI surgical patients for these nutritional interventions.