Individual Gut Microbiome Influences the Impact of Inulin and Psyllium on Colitis

By Andreu Prados, PhD, BPharm, RDN, and Natasha Haskey PhD, RD

Patients with inflammatory bowel diseases (IBD) often avoid foods with fiber for fear of triggering or worsening symptoms. However, emerging findings in humans¹ found the impact of fiber on gut inflammation is shaped by factors such as the type of fiber, the immune status of the patient, and the fermentative capacity of their gut microbiota. Within dietary fibers, some soluble fibers are readily fermented by the gut microbiome (i.e., inulin), while other soluble fibers (i.e., psyllium) are poorly fermented by gut microbes.

A new study² led by Benoit Chassaing from Université Paris Cité found that each person responds in a different way to soluble dietary fibers, suggesting that the recommendation of fiber intake in individuals with IBD should be individualized.

To study the impact of fibers on the gut microbiome, the researchers incubated feces from healthy donors with inulin or psyllium (both soluble fibers), with cellulose-treated feces used as a reference. It turned out that inulin and psyllium caused changes in microbiome composition, bacterial metabolites, and inflammation only in select donors (fiber-sensitive microbiome). In contrast, the microbiome of other donors enriched with Faecalibacterium prausnitzii –an anti-inflammatory commensal bacterium that is often reduced in people with Crohn’s disease– was minimally affected (fiber-resistant microbiome). Simply put, the impact of dietary fibers on the microbiome displays a remarkable degree of variation between individuals.

What is interesting to note is that the fiber-sensitive microbiome was sufficient to promote colitis in mice with no living microorganisms, with intestinal inflammation exacerbated by inulin but not by psyllium. On the other hand, mice that received the fiber-resistant microbiome displayed colitis independently on the amount of fiber in their diet.

In conclusion, these findings support that the “one size fits all” dietary fiber advice for individuals with IBD is flawed because it assumes all microbiomes process dietary fiber in the same way. The reality is that the extent to which select fibers promote colitis is highly influenced by an individual’s gut microbiome and thus, the advice of avoiding fiber should not be generalized to every person with IBD.

^{1. Armstrong, H. K., Bording-Jorgensen,et. al.(2023). Unfermented β-fructan Fibers Fuel Inflammation in Select Inflammatory Bowel Disease Patients. Gastroenterology, 164(2), 228–240. https://doi.org/10.1053/j.gastro.2022.09.034
‍2. Bonazzi, E., Bretin, A., Vigué, L. et al. Individualized microbiotas dictate the impact of dietary fiber on colitis sensitivity. Microbiome12, 5 (2024). https://doi.org/10.1186/s40168-023-01724-6}

^‍‍About the writers:

‍Dr. Andreu Prados is a science and medical writer specializing in making reliable evidence of non-prescription therapeutics for gastrointestinal conditions understandable, engaging and ready for use for healthcare professionals and patients. He holds bachelor’s degrees in Pharmacy and Human Nutrition and Dietetics and a PhD in nutrition communication.

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Dr. Natasha Haskey is a clinical scientist and Registered Dietitian with over 20 years of practical experience in nutrition therapy for IBD.  In 2022, she completed her doctorate at the Center for Microbiome and Inflammation Research at the University of British Columbia in Okanagan, Canada, examining how a Mediterranean diet influenced clinical disease activity, inflammation and the microbiome in ulcerative colitis. She co-authored the textbook called "Gut Microbiota: Interactive effects on nutrition and health"

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