Low-dose carrot rhamnogalacturonan-I (cRG-I) has shown consistent modulatory effects on the gut microbiota and immune function in humans. In this study we investigated its effects on the microbial composition and metabolite production of the gut microbiota of small (5–10 kg), medium-sized (10–27 kg), and large (27–45 kg) dogs, using inulin and xanthan as comparators. Fecal samples from six dogs of each size group were evaluated. Overall microbiome composition, assessed using metagenomic sequencing, was shown to be driven mostly by dog size and not treatment. There was a clear segregation in the metabolic profile of the gut microbiota of small dogs versus medium-sized and large dogs. The fermentation of cRG-I specifically increased the levels of acetate/propionate-producing Phocaeicola vulgatus. cRG-I and inulin were fermented by all donors, while xanthan fermentation was donor-dependent. cRG-I and inulin increased acetate and propionate levels. The responses of the gut microbiota of different sized dogs to cRG-I were generally consistent across donors, and interindividual differences were reduced. This, together with the significant increase in P. vulgatus during fermentation in both this study and an earlier human ex vivo study, suggests that this abundant and prevalent commensal species has a core capacity to selectively utilize cRG-I.

Unusually frequent and soft stools may negatively impact the quality of life. A postbiotic containing heat inactivated Limosilactobacillus fermentum CNCM I-2998 and Lactobacillus delbrueckii subsp. lactis CNCM I-4831 has previously been shown to alleviate gastrointestinal symptoms and diarrhea in patients with clinically diagnosed gastrointestinal disorders. This study evaluated whether this postbiotic can support bowel movement frequency in Japanese healthy adults with self-reported frequent and soft stools. In a randomized, double-blind, placebo-controlled clinical trial, participants (n = 100) received the postbiotic (20 billion heat-inactivated cells per day) or placebo for four weeks. The primary endpoint was weekly bowel movement frequency. Secondary endpoints included days with bowel movements per week, sense of relief, stool characteristics (shape, color, odor, water content), gastrointestinal symptoms, and fecal microbiome composition. After four weeks, the postbiotic group showed significantly lower bowel movement frequency and fewer days with bowel movements when compared with the placebo group. Importantly, these reductions were not accompanied by decreased stool volume or increased hard stools or constipation symptoms. Mild changes in microbiome composition were detected across groups, and no adverse events were reported. These findings suggest that the postbiotic is safe and can help reduce bowel movement frequency in healthy individuals experiencing unusually frequent and soft stools.