Bacterially synthesized folate and supplemental folic acid are absorbed across the large intestine of piglets

A large pool of folate exists in the large intestine of humans. Preliminary evidence, primarily in vitro, suggests that this folate may be bioavailable. The purpose of this study was to test the hypothesis that supplemental folic acid and bacterially synthesized folate are absorbed across the large intestine of piglets. The pig was used as an animal model because it resembles the human in terms of folate absorption, at least in the small intestine. A tracer of [3H]-folic acid or [3H]-para-aminobenzoic acid ([3H]-PABA), a precursor of bacterially synthesized folate, was injected into the cecum of 11-day-old piglets. Feces and urine were collected for 3 days. Thereafter, piglets were killed, and livers and kidneys harvested. [3H]-Folate was isolated from biological samples by affinity chromatography using immobilized milk folate binding proteins and counted using a scintillation counter. In piglets injected with [3H]-folic acid, the feces, liver, urine and kidneys accounted for 82.1%, 12.3%, 3.9% and 1.7% of recovered [3H]-folate, respectively. In piglets injected with [3H]-PABA, the amount of recovered bacterially synthesized folate in the feces, liver and urine was 85.1%, 0.4% and 14.6%, respectively. Twenty-three percent and 13% of tritium were recovered in samples examined (liver, kidney, fecal and urine) from piglets injected with [3H]-folic acid and [3H]-PABA, respectively. Using our estimates of [3H]-folic acid absorption and the total and percent monoglutamyl folate content of piglet feces, we predict that at least 18% of the dietary folate requirement for the piglet could be met by folate absorption across the large intestine.