Gut Microbiome Patterns Linked to IBS-D Response to Rifaximin, Diet

Key Takeaways

• Five-week decreases in abdominal pain and bloating were comparable after rifaximin and low FODMAP diet counseling.
• Baseline microbiome features differed among low FODMAP responders, rifaximin responders, and patients who did not respond to either approach.
• The authors described these microbial associations as hypothesis-generating and said validation is still needed.

In a single-center randomized IBS-D comparison, 65 adults with IBS-D who received 14 days of rifaximin or low FODMAP counseling had similar symptom improvement at five weeks. Both groups had comparable and significant decreases in abdominal pain and bloating during short-term follow-up. The head-to-head design compared an antibiotic strategy with structured dietary counseling within the same randomized study population. Baseline stool microbiome patterns also appeared to differ between patients who responded and those who did not. Those microbial observations were described as exploratory signals for future research, not clinically established markers for treatment selection.

The trial was a single-center randomized controlled study in adults with IBS-D, published in Clinical Gastroenterology and Hepatology. Participants were assigned to rifaximin or low FODMAP diet counseling, with treatment delivered over 14 days and outcomes reviewed after five weeks. Stool samples were collected at weeks 0, 2, 4, and 5, allowing investigators to track microbiome features across treatment and follow-up. Researchers examined whether specific bacterial patterns aligned with treatment response and with improvement in individual symptoms during the study period. Breath tests were also performed, but they did not predict response, leaving the microbiome analysis as the main distinguishing feature of the trial.

Patients who responded to the low FODMAP diet had lower baseline abundance of putative saccharolytic taxa before treatment began. Over time, that group also showed increases in microbial diversity, adding a longitudinal feature to the diet-associated response pattern. Rifaximin responders, by contrast, were enriched at baseline in taxa with potential short-chain fatty acid-producing and bile acid-modifying capabilities. Those response-associated features differed from the profile seen among patients who failed to improve with either intervention. Nonresponders to both approaches were enriched in putative proteolytic taxa, forming a separate observational signature within the randomized cohort.

Investigators said these microbial associations should be viewed as hypothesis-generating rather than definitive and emphasized that the reported patterns still require external validation. They did not present the observed taxa as clinically ready predictors or suggest that routine selection tools have been established. The researchers also described gut microbial testing as a possible future route toward more precise treatment recommendations if later studies confirm the signal. That framing remained tentative, clearly separating future potential from current evidence. Overall, short-term symptom relief was similar across both interventions, while the microbiome differences remained exploratory and not yet practice-ready.