The Role of Probiotics, Prebiotics, and Synbiotics for Reducing Chemotherapy-Induced Gastrointestinal Toxicity: A Systematic Review and Meta-Analysis

Background Chemotherapy-induced gastrointestinal toxicity remains a major clinical problem that limits treatment adherence and quality of life in cancer patients. Microbiota-modulating interventions such as probiotics, prebiotics, and synbiotics have been proposed as supportive therapies, yet their comparative effectiveness remains unclear. Objective This systematic review and meta-analysis evaluated the effectiveness of probiotics, prebiotics, and synbiotics in reducing chemotherapy-induced gastrointestinal toxicity in cancer patients. Methods A systematic search of PubMed, Scopus, Cochrane Library, and ClinicalTrials.gov was performed between March and August 2025 to identify randomized controlled trials (RCTs) involving chemotherapy-treated cancer patients with gastrointestinal toxicities. Studies comparing probiotics, prebiotics, or synbiotics with placebo or standard care were included. Two reviewers independently screened studies, extracted data, and assessed risk of bias using standardized criteria. Meta-analysis was conducted using RevMan 5.4. Results Twenty-nine RCTs were included, comprising probiotics (n = 17), prebiotics (n = 6), and synbiotics (n = 6). Probiotic supplementation, predominantly containing Lactobacillus and Bifidobacterium species, significantly reduced the incidence of chemotherapy-induced diarrhea (RR = 0.67; 95% CI 0.47–0.95; p = 0.03). Synbiotics demonstrated an even greater protective effect (RR = 0.51; 95% CI 0.29–0.89; p = 0.02). Evidence supporting prebiotics alone was limited and inconsistent. Conclusion Probiotics and synbiotics may be effective in reducing chemotherapy-induced gastrointestinal toxicity, with the most consistent evidence for diarrhea.