While assessment of folate requirements has been based only on dietary intakes, folate produced by the colonic microflora can exceed amounts consumed in food. Bacterially synthesized folate is absorbed across the rat and piglet colon. In vitro studies suggest, but direct evidence is lacking that folate is absorbed across the intact human colon. If indeed folate is absorbed, the amount synthesized may be susceptible to manipulation by fibre and prebiotics intake. We therefore performed two studies to investigate folate absorption across the colon. To confirm absorption across the intact human colon, in our first study, 684 nmol (320 µg) 13C5-glutamyl-[6S]-5-formyltetrahydrofolate was infused into the cecum of six adults and blood samples were collected. Tandem mass spectrometry confirmed folate absorption across the colon by appearance in plasma of 13C5-[6S]-5-methyltetrahydrofolate, at a rate of 0.6±0.2 nmol/h versus 7±1.2 nmol/h after intravenous injection of 172 nmol 13C5-5-formyltetrahydrofolate. Since bifidobacteria are potent folate producers, in our second study we evaluated the influence of bifidogenic oligosaccharides on colonic folate production and host folate status, using a piglet animal model. Piglets (n=12) were randomly assigned a milk-based formula with 5g/L inulin + 5g/L galactooligosaccharides, or 5g/L maltodextrin (control). After 28 days, the weights of colon contents (178 %) and colon tissue (37.9 %) of piglets fed oligosaccharides were greater than controls (P=0.0003, P=0.0044, respectively). The bacterial load and folate contents in the colons of piglets fed oligosaccharides were greater than controls (P=0.0022, P=0.0218, respectively). Body weights, blood folate status and liver and kidney folate concentrations did not differ. In conclusion, folate is absorbed across the human colon. Supplementation of the piglet diet with 5g/L inulin and 5g/L galactooligosaccharides increased the amounts of microbial folate, and the weights of colon tissue and contents, but folate concentrations in colon contents, blood and organs were not affected.

While assessment of folate requirements has been based only on dietary intakes, folate produced by the colonic microflora can exceed amounts consumed in food. Bacterially synthesized folate is absorbed across the rat and piglet colon. In vitro studies suggest, but direct evidence is lacking that folate is absorbed across the intact human colon. If indeed folate is absorbed, the amount synthesized may be susceptible to manipulation by fibre and prebiotics intake. We therefore performed two studies to investigate folate absorption across the colon. To confirm absorption across the intact human colon, in our first study, 684 nmol (320 µg) 13C5-glutamyl-[6S]-5-formyltetrahydrofolate was infused into the cecum of six adults and blood samples were collected. Tandem mass spectrometry confirmed folate absorption across the colon by appearance in plasma of 13C5-[6S]-5-methyltetrahydrofolate, at a rate of 0.6±0.2 nmol/h versus 7±1.2 nmol/h after intravenous injection of 172 nmol 13C5-5-formyltetrahydrofolate. Since bifidobacteria are potent folate producers, in our second study we evaluated the influence of bifidogenic oligosaccharides on colonic folate production and host folate status, using a piglet animal model. Piglets (n=12) were randomly assigned a milk-based formula with 5g/L inulin + 5g/L galactooligosaccharides, or 5g/L maltodextrin (control). After 28 days, the weights of colon contents (178 %) and colon tissue (37.9 %) of piglets fed oligosaccharides were greater than controls (P=0.0003, P=0.0044, respectively). The bacterial load and folate contents in the colons of piglets fed oligosaccharides were greater than controls (P=0.0022, P=0.0218, respectively). Body weights, blood folate status and liver and kidney folate concentrations did not differ. In conclusion, folate is absorbed across the human colon. Supplementation of the piglet diet with 5g/L inulin and 5g/L galactooligosaccharides increased the amounts of microbial folate, and the weights of colon tissue and contents, but folate concentrations in colon contents, blood and organs were not affected.