Gut microbiota in irritable bowel syndrome: a narrative review of mechanisms and microbiome-based therapiesOriginal paper
Karen Pendergrass is a microbiome researcher specializing in microbiome-targeted interventions (MBTIs). She systematically analyzes scientific literature to identify microbial patterns, develop hypotheses, and validate interventions. As the founder of the Microbiome Signatures Database, she bridges microbiome research with clinical practice. In 2012, based on her own investigative research, she became the first documented case of FMT for Celiac Disease, four years before the first published case study.
Read MoreWhat was studied?
This narrative review examined how gut microbiota drive irritable bowel syndrome (IBS) and how microbiome-based therapies perform. The authors searched PubMed and Web of Science for work published between January 2015 and July 2025. They took a mechanism-first, subtype-aware approach. They linked microbial outputs like short-chain fatty acids and bile acids to the gut barrier, immunity, and gut-brain signaling. They then mapped major treatments and graded their evidence certainty and safety.
Who was studied?
This was a review of human and animal literature, not a new patient cohort. IBS is a disorder of gut-brain interaction with a global prevalence estimated at 3 to 5 percent. The review covered the main IBS subtypes: diarrhea-predominant, constipation-predominant, and mixed. It prioritized systematic reviews, meta-analyses, and large randomized controlled trials. Evidence spanned fecal and mucosal sampling, 16S rRNA, and shotgun metagenomic studies across many countries.
What were the most important findings?
IBS patients showed reduced microbial diversity and an increased Firmicutes-to-Bacteroidetes ratio, most pronounced in the diarrhea subtype. Findings varied widely across studies due to sampling and sequencing differences. A meta-analysis of 35 trials (3,452 patients) found probiotics lowered symptom persistence versus placebo (RR 0.79, 95 percent CI 0.70 to 0.89). Rifaximin gave short-term relief in the TARGET trials (40.7 and 31.7 percent). Low-FODMAP diets improved symptoms in 80 percent of 117 patients. A meta-analysis of 10 fecal transplant trials (573 patients) found no significant symptom benefit.
What are the greatest implications of this study?
The review argues IBS care should shift from taxonomy toward microbial function and patient subtype. No single universal IBS microbiome signature exists. For most microbiome therapies, evidence certainty is low to very low by GRADE, and some guidelines suggest against routine probiotic use. The authors call for large, standardized, longitudinal multi-omics trials with consistent adverse-event reporting before precision microbiome treatments enter routine practice.