Orally Ingested Probiotic, Prebiotic, and Synbiotic Interventions as Countermeasures for Gastrointestinal Tract Infections in Non-elderly Adults: A Systematic Review and Meta-analysis

Document Type

Journal Article

Publication Date



Advances in nutrition (Bethesda, Md.)




dietary supplement; fermentable fiber; gastrointestinal illness; gut microbiome; infectious diarrhea; travelers’ diarrhea


Meta-analyses have not examined the prophylactic use of orally ingested probiotics, prebiotics, or synbiotics for preventing gastrointestinal tract infections (GTI) of various etiologies in adult populations despite evidence that these gut microbiota-targeted interventions can be effective in treating certain GTI. This systematic review and meta-analysis aimed to estimate the effects of prophylactic use of orally ingested probiotics, prebiotics, and synbiotics on GTI incidence, duration, and severity in non-elderly, non-hospitalized adults. CENTRAL, PubMed, Scopus, and Web of Science were searched through January 2022. English-language, peer-reviewed publications of randomized, placebo-controlled studies testing an orally ingested probiotic, prebiotic, or synbiotic intervention of any dose for ≥1 week in adults who were not hospitalized, immunosuppressed, or taking antibiotics were included. Results were analyzed using random-effects meta-analyses of intention-to-treat (ITT) and complete case (CC) cohorts. Heterogeneity was explored by subgroup meta-analysis and meta-regression. Risk of bias was assessed using the Cochrane RoB2 tool. Seventeen publications reporting 20 studies of probiotics (n=16), prebiotics (n=3), and synbiotics (n=1) were identified (n>6,994 subjects). In CC and ITT analyses, risk of experiencing ≥1 GTI was reduced with probiotics (CC analysis: risk ratio=0.86 [95%CI: 0.73, 1.01]) and prebiotics (risk ratio=0.80 [95%CI: 0.66, 0.98]). No effects on GTI duration or severity were observed. Sources of heterogeneity included study population and number of probiotic strains administered, but were often unexplained, and a high risk of bias was observed for most studies. Specific effects of individual probiotic strains and prebiotic types could not be assessed due to a lack of confirmatory studies. Findings indicated that orally ingested probiotics and prebiotics, relative to placebo, both demonstrated modest benefit for reducing GTI risk in non-elderly adults. However, results should be interpreted cautiously due to the low number of studies, high risk of bias, and unexplained heterogeneity that may include probiotic strain- or prebiotic-specific effects. PROSPERO REGISTRATION: CRD42020200670.