An adequate and balanced supply of nutrients is essential for maintaining health, and an optimal immune response is fast, contained and properly controlled, curbing infections quickly while minimizing damage. Several micronutrients contribute to normal immune function and certain dietary fibers, for example pectic polysaccharides, can play an important role in educating and regulating immune cell responses. The aim of this paper is to elaborate on our initial findings that dietary supplementation with carrot-derived rhamnogalacturonan-I (cRG-I) accelerates and augments local innate immune and anti-viral interferon response to a rhinovirus-16 (RV16) infection and reduces the severity and duration of symptoms in humans. Dietary intake of cRG-I also enhanced immune responses to this respiratory viral infection as measured by ex vivo stimulation of whole blood with the Toll-like receptor 3 (TLR3) ligand polyinosinic:polycytidylic acid and NK cell function. Consumption of cRG-I also reduced the negative effects of this common cold infection on quality of life as assessed by individual symptom scores. RG-I from carrot is a safe, sustainable, and economically viable solution that could easily be integrated into food products and dietary supplements aiming to support immune fitness and wellbeing.

Background: Using dietary interventions to steer the metabolic output of the gut microbiota towards specific health-promoting metabolites is often challenging due to interpersonal variation in treatment responses. Methods: In this study, we combined the ex vivo SIFR^® (Systemic Intestinal Fermentation Research) technology with untargeted metabolite profiling to investigate the impact of carrot-derived rhamnogalacturonan-I (cRG-I) on ex vivo metabolite production by the gut microbiota of 24 human adults. Results: The findings reveal that at a dose equivalent to 1.5 g/d, cRG-I consistently promoted indole-3-propionic acid (IPA) production (+45.8% increase) across all subjects. At a dose equivalent to 0.3 g/d, increased IPA production was also observed (+14.6%), which was comparable to the effect seen for 1.5 g/d inulin (10.6%). IPA has been shown to provide protection against diseases affecting the gut and multiple organs. The Pearson correlation analysis revealed a strong correlation (R = 0.65, p_adjusted = 6.1 × 10⁻¹⁶) between the increases in IPA levels and the absolute levels of Bifidobacterium longum, a producer of indole-3-lactic acid (ILA), an intermediate in IPA production. Finally, the community modulation score, a novel diversity index, demonstrated that cRG-I maintained a high α-diversity which has previously been linked to elevated IPA production. Conclusions: The results from the ex vivo SIFR^® experiment mirrored clinical outcomes and provided novel insights into the impact of cRG-I on the gut microbiome function. Importantly, we demonstrated that cRG-I promotes tryptophan conversion into IPA via gut microbiome modulation, thus conferring benefits via amino acid derived metabolites extending beyond those previously reported for short chain fatty acids (SCFA) resulting from carbohydrate fermentation.

Background: Rhamnogalacturonan-I (RG-I) is a pectic polysaccharide with emerging prebiotic and immunomodulatory potential. This randomised, double-blind, placebo-controlled trial (ID: NCT06081972) evaluated the effects of carrot-derived RG-I (cRG-I) supplementation, compared to placebo (maltodextrin), on gut microbiota composition and immune cell activation in healthy adults. Methods: A total of 54 participants (18–70 years old) were randomised in a double-blind manner to receive either 500 mg/day of cRG-I or placebo for four weeks. Pre-screening ensured balanced randomisation based on habitual fibre intake and faecal Bifidobacterium counts. Questionnaires assessed potential gut health and well-being effects, while in vitro and ex vivo models were used to evaluate effects on intestinal permeability. Results: cRG-I was well tolerated with excellent compliance. Faecal Bifidobacterium counts increased significantly, peaking at week 3. Isobutyric acid levels rose, though no other SCFAs differed. Immunologically, cRG-I enhanced the percentage of circulating myeloid dendritic cells expressing activation markers (CD86, HLA-DR) on. Stool consistency improved slightly. Preclinical models further showed that cRG-I and its fermentation products protected intestinal barrier integrity under stress. Conclusion: These results support cRG-I as a safe, low-dose dietary intervention capable of beneficially modulating gut microbiota, immune responses, and barrier function in healthy adults within a short supplementation period.

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.