Irritable Bowel Syndrome and the Microbiome
July 14, 2020 by Flore Clinical Editorial
Irritable bowel syndrome affects 10-15% of the global population and represents the most common reason for gastroenterology referral. Its pathophysiology is multifactorial — visceral hypersensitivity, altered gut motility, intestinal permeability, immune activation, and microbiome dysbiosis all contribute. Understanding the microbial dimension opens therapeutic avenues that dietary and pharmacological approaches alone cannot address.
Microbiome Alterations in IBS
Compared to healthy controls, IBS patients show reduced microbial diversity, decreased Lactobacillus and Bifidobacterium species, elevated Firmicutes:Bacteroidetes ratio, and increased abundance of gas-producing Veillonella and Streptococcus species. These findings are replicated across subtypes with subtype-specific variation: IBS-D shows more pronounced Bacteroides excess; IBS-C shows greater methanogen prevalence (see SIBO article).
Leaky Gut and Immune Activation
Intestinal permeability is elevated in a subset of IBS patients, particularly post-infectious IBS (PI-IBS), which follows acute gastroenteritis in 5-30% of cases. Elevated zonulin, reduced claudin-1, and mucosal immune activation are measurable biomarkers in this population. Addressing barrier dysfunction — through butyrate, Akkermansia-promoting strategies, and targeted probiotics — is a critical component of treatment. See our leaky gut article for detailed mechanisms.
Evidence-Based Probiotic Interventions
A 2018 systematic review in Alimentary Pharmacology & Therapeutics analyzed 53 RCTs of probiotic therapy in IBS, finding significant improvement in overall symptom score (RR 1.82, 95% CI 1.41-2.35) and abdominal pain. B. infantis 35624 (Align) and multi-strain combinations showed the most consistent results. The Rome IV criteria now acknowledge the microbiome as a therapeutic target.
Clinical Protocol Considerations
For clinicians, a practical approach includes: ruling out SIBO via lactulose breath test, assessing stool microbiome composition, identifying trigger dietary patterns (low-FODMAP as a diagnostic tool), and targeting specific deficits with precision probiotics. Response typically emerges over 4-12 weeks; non-responders warrant reassessment of diagnosis and microbiome profile.
See also: IBD: A Microbial Perspective · Short Chain Fatty Acids