CAROTENOIDS MODULATE EX VIVO FERMENTATION OF INULIN USING IBS AND OVERWEIGHT ADULT GUT MICROBIOTA

Carotenoids have direct antioxidant and anti-inflammatory benefits. Because of their low bioavailability, a portion of carotenoids also reaches the colon, but their interactions with the gut microbiome remain poorly understood.Methods: We investigated how beta-carotene (BC), lutein (LU), lycopene (LY), and zeaxanthin (ZE), at biologically relevant doses (1 to 60 mg per day), affect the composition and metabolite production of adult gut microbiota from individuals with irritable bowel syndrome (IBS) and overweight (OW). Experiments were performed using the ex vivo SIFR fermentation system (Systemic Intestinal Fermentation Research). Fresh fecal samples were collected from 12 donors (n = 6 per cohort) and incubated under anaerobic conditions for 24 hours, with carotenoids tested alone or together with the prebiotic inulin (IN, at 2.5 g per day).Results: Each cohort showed distinct microbiota profiles at baseline. Carotenoids alone caused only minor changes, but when combined with inulin they significantly altered microbial community composition (Bray-Curtis dissimilarity, P < 0.05) and increased short-chain fatty acid (SCFA) production. Most carotenoids increased butyrate levels compared with inulin alone. ZE at 2 mg per day in IBS (+7.6 percent) and LU at 60 mg per day in OW (+8.0 percent) produced the strongest butyrate increases (P adjusted < 0.10). In contrast, LY at 45 mg per day increased acetate (+3.5 percent) and propionate (+8.0 percent) while reducing butyrate (-7.5 percent, P adjusted < 0.10). SCFA changes were linked to carotenoid- and cohort-specific shifts in the abundance of Bifidobacterium, Alistipes, Akkermansia, Faecalibacterium, and Coprococcus. ZE enhanced the inulin-induced increase of the health-related metabolites 3-phenyllactic acid (PLA) and 2-hydroxyisocaproic acid (HICA), especially in IBS subjects (P adjusted < 0.20).Conclusions: Antioxidant carotenoids may support anaerobic gut microbes, including key butyrate producers, and may help counteract phenotype-specific dysbiosis in IBS and overweight individuals. As these benefits occurred when carotenoids were combined with inulin, carotenoids may have stronger effects when consumed with fiber-rich diets, reflecting their natural presence in plant-based foods.