Tannin supplementation influences gut microbiota composition and activity in IBS-D patients with a potential impact on symptoms: A pilot study

There is still no recognized therapy for irritable bowel syndrome, subtype diarrhea (IBS-D), however the involvement of the gut microbiota in its etiopathology is well understood, a preliminary, quasi-experimental, before-after and prospective study was conducted on 28 patients to test the effect of a tannin-based supplement, on the composition and the activity of microbiota, after 8 weeks of treatment. No statistically significant differences were found in alpha or beta-diversity. However, sparse Partial Least Squares Discriminant Analysis (sPLS-DA) and Boruta algorithm did reveal relevant changes in the relative abundance of specific groups of bacteria, highlighting the involvement of recognized of IBS-D biomarkers. The modulation of the composition of the gut microbiota had an impact also in the production of short chain fatty acids, which were modulated in a healthier way: acetate and butyrate (n.s. and p < 0.001) increased while propionate and formate (p = 0.005 and p < 0.001) resulted to be significantly reduced following the supplementation. The sPLS analysis showed that the strongest association between faecal microbiome composition and clinical symptoms of IBS-D was given by Catenibacterium, which showed a positive correlation with frequency of stool deposition (r = 0.615)