Gut Microbiome Modulation in Irritable Bowel Syndrome: A Systematic Review of Probiotics, Prebiotics, and Fecal Microbiota Transplantation
Background
Irritable bowel syndrome (IBS) affects approximately 11% of the global population and is increasingly recognized as a disorder of gut-brain interaction with altered intestinal microbiota. Microbiome-targeted therapies including probiotics, prebiotics, synbiotics, and fecal microbiota transplantation (FMT) have been proposed as treatment strategies. However, evidence remains fragmented and heterogeneous, complicating clinical decision-making.
Methods
We conducted a systematic review following PRISMA 2020 guidelines. Databases including PubMed, Embase, Web of Science, and Cochrane Central Register of Controlled Trials were searched from January 2015 through September 2025. Eligible studies were randomized controlled trials evaluating microbiome-targeted interventions in adults meeting Rome IV criteria for IBS, with a minimum treatment duration of 4 weeks. Primary outcomes were global IBS symptom improvement and abdominal pain severity. Quality assessment was performed using the Cochrane Risk of Bias 2 tool.
Results
Forty-seven randomized controlled trials (n=8,912 participants) met inclusion criteria. For probiotics, 31 trials demonstrated that multi-strain formulations containing Bifidobacterium longum, Lactobacillus acidophilus, and Lactobacillus plantarum showed the most consistent benefit, with pooled relative risk of global symptom improvement of 1.44 (95% CI, 1.28-1.62). Single-strain probiotics showed variable results. For prebiotics, 8 trials of partially hydrolyzed guar gum and galactooligosaccharides showed modest improvement in bloating scores but inconsistent effects on overall symptoms. For FMT, 8 trials showed conflicting results, with response rates ranging from 24% to 65%, likely reflecting heterogeneity in donor selection, delivery method, and patient selection. Adverse events across all interventions were generally mild and gastrointestinal in nature.
Conclusions
Multi-strain probiotic formulations demonstrate the most robust evidence for symptom management in IBS. FMT shows promise but requires standardization of protocols and better patient selection criteria before clinical implementation can be recommended.
Multi-strain probiotics containing Bifidobacterium and Lactobacillus species show the most consistent evidence for symptom improvement in IBS, while fecal microbiota transplantation results remain inconclusive and require further investigation.