PARIS — Irritable bowel syndrome (IBS) is a common brain-gut axis disorder, and patients are often dissatisfied with conventional treatments.
The role of the microbiota in IBS is now well established, and patients frequently take probiotics on their own initiative or on the advice of a physician or pharmacist. However, not all probiotics have equal efficacy, so which ones should be recommended?
Jean-Marc Sabaté, MD, PhD, a gastroenterologist at Avicenne Hospital in Bobigny, France, shared insights about probiotics at the Francophone Days of Hepatology, Gastroenterology, and Digestive Oncology.
IBS, according to the Rome IV symptom-based classification, is a “disorder of brain-gut axis interactions” with a prevalence of about 4% in the adult population. In France, during an average care pathway of about 8 years, patients try an average of five therapeutic strategies (and as many as 11), including antispasmodics (85%), diets (78%), and probiotics. In addition, 66.4% of patients had either taken or were taking probiotics at the time of a recent survey.
While the 2022 recommendations from the American College of Gastroenterology on the diagnosis and management of IBS do not support the use of probiotics for overall symptom relief — a recommendation for which they cite a low level of evidence — “there is nevertheless a rationale for prescribing probiotics in IBS due to the significant role of the microbiota (or dysbiosis) in this condition,” said Dr. Sabaté.
Microbiota in IBS
Evidence indicating that antibiotics exacerbate IBS symptoms and revealing chronic bacterial overgrowth in the small intestine of patients with IBS supports the role of the microbiota. Studies using a molecular approach (16s rRNA) have settled the debate, confirming differences in the intestinal flora between patients with IBS and healthy subjects. Data also indicate differences in flora between patient subtypes, such as an increased Firmicutes to Bacteroidetes ratio. However, one subgroup, which can represent as much as a third of patients, seems to harbor a “normal” microbiota.
Nonetheless, the microbiota plays a significant role in IBS. A Swedish study highlighted the influence of bacterial enterotypes on transit type associated with IBS and symptom severity, independent of diet composition or medication use.
This dysbiosis could play a significant role as it interacts with other mechanisms involved in IBS, including changes in intestinal motility related to diet (related to fermentable carbohydrates, for example). Moreover, the microbiota seems to induce a low level of immune activation in patients with IBS, leading to microinflammation and increased intestinal permeability, especially after an infection.
Furthermore, alterations in the regulation of bile acid deconjugation by the microbiota partly explain the frequency and consistency of stools in diarrhea-predominant IBS patients.
In addition, colonic gas production is higher in these patients. Those complaining of flatulence have poor tolerance to intestinal gases after a flatulent meal, associated with microbiota instability.
Data regarding the interaction between the microbiota and central mechanisms mainly come from animal studies. In rodents, microbiota constituents seem to affect brain development, function, and morphology. Emotional and physical traumas during childhood appear to be risk factors. Moreover, even brief exposure to broad-spectrum antibiotics in neonates could cause subsequent visceral hypersensitivity.
Lastly, the role of the microbiota in changes in medullary pain control after visceral stimulation (eg, rectal distension) has still not been demonstrated in humans.