Twenty-one RCTs (2,730 participants) were included in the review. In three multiple-arm trials, two intervention groups were compared with one control group, so the results were based on a total of 24 comparisons from the 21 studies. Twelve trials were considered to be of high quality. Eleven trials used an intention-to-treat analysis.
Immunonutrition significantly reduced overall postoperative complications, irrespective of whether it was given before surgery (OR 0.48, 95% CI 0.34 to 0.69; six RCTs), both before and after surgery (OR 0.39, 95% CI 0.28 to 0.54; five RCTs) or only after surgery (OR 0.46, 95% CI 0.25 to 0.84; eight RCTs).
Immunonutrition significantly reduced postoperative infection when given before surgery (OR 0.36, 95% CI 0.24 to 0.56), both before and after surgery (OR 0.41, 95% CI 0.28 to 0.58) or only after surgery (OR 0.53, 95% CI 0.40 to 0.71). Although all trials provided data on postoperative infection, it was not clear how many provided data for each timing of intervention.
No significant heterogeneity between trials was found for overall complications or postoperative infection.
Immunonutrition led to a shorter hospital stay (MD −2·12 days, 95% CI −2·97 to −1·26), based on 21 comparisons (2,279 participants), but there was substantial heterogeneity between the trials (I2=81%). Mean differences of similar magnitude were found for all three timings of intervention.
The beneficial effects of immunonutrition were confirmed when low-quality trials were excluded. Perioperative immunonutrition had no influence on mortality. Six trials that assessed tolerance found no difference in the risk of an intolerance event between the intervention and control groups.
There was no evidence of publication bias for postoperative infectious complications and mortality. Funnel plots for overall complications showed minor asymmetry (I2=27%); hospital stay showed major asymmetry (I2=81%).