Dietary Supplementation of Vitamin B12 to Rats Fed High-Amylose Cornstarch Normalizes Propionate Fermentation in the Colon.

Since propionate exerts several physiological effects, maintenance of its normal colonic fermentation is essential. To investigate whether vitamin B₁₂ (VB₁₂) is essential for normal propionate fermentation by colonic bacteria, via the succinate pathway, we examined if high-amylose cornstarch (HACS) feeding activated such a pathway, if high HACS feeding impaired propionate fermentation, and if oral VB₁₂ supplementation normalized propionate fermentation. Male rats were given control, 20% HACS or 3% fucose diets (Expt. 1); a VB₁₂-free control diet or one supplemented with 5-30% HACS (Expt. 2); and the 20% HACS diet supplemented with 0.025-25 mg/kg of VB₁₂ (Expt. 3), for 14 d. HACS feeding significantly increased cecal succinate concentration, activating the succinate pathway (Expt. 1). Cecal cobalamin concentration in 20% and 30% HACS groups was about 75% of that in the control group (Expt. 2). Cecal succinate and propionate concentrations significantly increased and decreased in 30% HACS groups, respectively, compared with the control group. Although HACS group supplemented with 0.025 mg/kg of VB₁₂ had a low concentration of cecal propionate, adding high amounts of VB₁₂ to HACS diets provided sufficient amounts of VB₁₂ to rat ceca and increased cecal propionate concentration (Expt. 3). Compared with the non-HACS group, the relative abundance of Akkermansia muciniphila, but not Bacteroides/Phocaeicola, was lower in the HACS counterpart and showed improvement with increased VB₁₂ doses. To summarize, feeding high HACS decreased and increased cecal VB₁₂ and succinate concentrations, respectively. Furthermore, colonic delivery of sufficient amounts of VB₁₂ to rats likely reduced accumulation of succinate and normalized propionate fermentation.