In a new study published in Clinical gastroenterology and hepatologya low FODMAP diet and the antibiotic rifaximin produced similar significant relief in patients with irritable bowel syndrome with diarrhea (IBS-D).
The researchers also looked at distinct characteristics of patients’ gut microbiota to predict whether they would respond to a low FODMAP diet or rifaximin, or whether they would not respond to treatment.
Importantly, they discovered that differences in the gut microbiome may help predict which patients will respond to certain treatments. ”
Allen Lee, MD, MS, Assistant Professor of Internal Medicine, University of Michigan Medical School, first author of the paper
“We also identified distinct microbial signatures among patients who did not respond to either treatment. This suggests that we may be able to identify patients who do not respond to common microbiome-based treatments, such as rifaximin or a low-FODMAP diet, before starting treatment.”
Irritable bowel syndrome affects 10% to 15% of adults in the United States and is characterized by symptoms such as abdominal pain, bloating, and changes in bowel habits.
A low FODMAP diet is a proven treatment that eliminates certain carbohydrate-containing foods.
Still, the low-FODMAP diet and rifaximin each work in less than half of patients.
In addition to comparing a low-FODMAP diet with rifaximin, the researchers aimed to investigate the possibility that gut microbiome testing could one day allow for more accurate treatment recommendations.
“Currently, treating IBS often requires a trial-and-error approach, with patients undergoing multiple treatments until they find one that works. This can be frustrating, time-consuming, and burdensome for patients,” Lee said.
“Our research is motivated by emerging evidence that the gut microbiome plays an important role in irritable bowel syndrome, and differences in these microorganisms may help explain why some patients respond to certain treatments while others do not. By better understanding these patterns, we hope to move toward a personalized approach to care.”
In this single-center randomized controlled trial, 65 subjects were assigned to either 14 days of rifaximin or low FODMAP dietary counseling.
After 5 weeks, both groups had similar and significant reductions in abdominal pain and bloating.
Meanwhile, stool samples were collected at weeks 0, 2, 4, and 5 for analysis of participants’ gut microbiome.
The researchers were able to analyze whether specific bacteria predict treatment response and how differences in microbiome characteristics correspond to symptom improvement.
(Breath tests were also performed, but were found to be ineffective in predicting treatment response.)
Among their findings included that patients who responded to a low-FODMAP diet had lower baseline abundances of putative glycolytic taxa and showed increased microbial diversity over time.
On the other hand, rifaximin responders were enriched with taxa with potential short-chain fatty acid generation and bile acid modification abilities, suggesting that the microbial community is more resistant to antibiotic exposure.
Of note, patients who did not respond to either treatment were enriched in putative proteolytic taxa, highlighting distinct microbial profiles associated with treatment resistance.
Ultimately, the researchers stress that their findings are “hypothesis-generating rather than definitive.”
They hope future validation will lead to more personalized clinical therapy.
sauce:
Michigan Medicine – University of Michigan
Reference magazines:
Lee, A. others. (2026). A randomized trial of rifaximin and a low FODMAP diet on symptom outcomes and microbiome changes in irritable bowel syndrome. Clinical gastroenterology and hepatology. DOI: 10.1016/j.cgh.2026.04.014. https://www.cghjournal.org/article/S1542-3565(26)00316-2/abstract
