Abstract: We identified 81 studies that comprised 9072 participants for inclusion in our review. We categorised many studies at high or unclear risk of the bias' assessed. There was statistical evidence that use of CG reduced TFF [overall reduction of 10.4 hours (95% CI: -11.9, -8.9): 12.5 hours (95% CI: -17.2, -7.8) in CRS, 7.9 hours (95% CI: –10.0, -5.8) in CS, 10.6 hours (95% CI: -12.7, -8.5) in OS]. There was also statistical evidence that use of CG reduced TBM [overall reduction of 12.7 hours (95% CI: -14.5, -10.9): 18.1 hours (95% CI: -25.3, -10.9) in CRS, 9.1 hours (95% CI: -11.4, -6.7) in CS, 12.3 hours (95% CI: -14.9, -9.7) in OS]. There was statistical evidence that use of CG slightly reduced LOHS [overall reduction of 0.7 days (95% CI: -0.8, -0.5): 1.0 days in CRS (95% CI: -1.6, -0.4), 0.2 days (95% CI: -0.3, -0.1) in CS, 0.8 days (95% CI: -1.1, -0.5) in OS]. There was statistical evidence that use of CG slightly reduced TBS [overall reduction of 5.0 hours (95% CI: -6.4, -3.7): 3.21 hours (95% CI: -7.0, 0.6) in CRS, 4.4 hours (95% CI: -5.9, -2.8) in CS, 6.3 hours (95% CI: -8.7, -3.8) in OS]. Effect sizes were largest in CRS and smallest in CS. There was statistical evidence of heterogeneity in all analyses other than TBS in CRS. There was little difference in mortality, infection risk and readmission rate between the groups. Some studies reported reduced nausea and vomiting and other complications in the intervention group. CG was generally well-tolerated by participants. There was little difference in cost between the groups in the two studies reporting this outcome. Sensitivity analyses by quality of studies and robustness of review estimates revealed no clinically important differences in effect estimates. Sensitivity analysis of ERAS studies showed a smaller effect size on TFF, larger effect size on TBM, and no difference between groups for LOHS. Meta-regression analyses indicated that surgical site is associated with the extent of the effect size on LOHS (all surgical subgroups), and TFF and TBM (CS and CRS subgroups only). There was no evidence that ROB score predicted the extent of the effect size on any outcome. Neither variable explained the identified heterogeneity between studies. This review identified some evidence for the benefit of postoperative CG in improving recovery of GI function. However, the research to date has primarily focussed on CS and CRS, and largely consisted of small, poor quality trials. Many components of the ERAS programme also target ileus, therefore the benefit of CG alongside ERAS may be reduced, as we observed in this review. Therefore larger, better quality RCTS in an ERAS setting in wider surgical disciplines would be needed to improve the evidence base for use of CG after surgery.

Plain-language summary: This review found 81 relevant studies that recruited over 9000 participants in total. The studies mainly focussed on people having bowel surgery or caesarean section, but there were some studies of other surgery types. There were few studies of children. Most studies were of poor quality, which may mean their results are less reliable. We found some evidence that people who chewed gum after an operation were able to pass wind and have bowel movements sooner than people who did not chew gum. We also found some evidence that people who chewed gum after an operation had bowel sounds (gurgling sounds heard using a stethoscope held to the abdomen) slightly sooner than people who did not chew gum. There was a small difference in how long people stayed in hospital between people who did or did not chew gum. There were no differences in complications (such as infection or death) between people who did or did not chew gum. There was also no difference in the overall cost of treatment between people who did or did not chew gum. There is some evidence that chewing gum after surgery may help the digestive system to recover. However, the studies included in this review are generally of poor quality, which meant that their results may not be reliable. We also know that there are many factors affecting ileus, and that modern treatment plans attempt to reduce risk of ileus. Therefore to further explore using chewing gum after surgery, more studies would be needed which are larger, of better quality, include different types of surgery, and consider recent changes in health care systems.