Absorption and Malabsorption of Dietary Folate

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Abstract
Dietary folate exists largely as polyglutamates which are deconjugated by pancreatic (and other?) enzymes. After absorption, folate is apparently reconjugated, since it is found principally as a polyglutamate within the liver, red cells, and white cells. Mixed daily diets prepared under ordinary circumstances contain approximately 200 µg of folate according to S. faecalis assay, and an additional 400–500 µg of folate material active for L. casei only. Formyl folates are probably derived largely from vegetable sources, whereas methyl folates are derived largely from meats. Formyl folates are active in human nutrition. Unaltered PGA is capable of crossing the intestinal mucosa. There is evidence that this compound displaces previously-formed 5N-methyltetrahydrofolate from the liver and is itself subsequently converted into this form. Other pteridines are capable of displacing folate. Cellulose fibers may bind folate and interfere with its absorption. Dietary deficiency of folate does not appear to cause significant alteration in the small bowel mucosa. In tropical sprue a small bowel lesion probably precedes systemic folate depletion. The suggestion is made that a seemingly innocuous dietary component that is similar to folic acid in chemical structure may displace the authentic vitamin producing an injury in intestinal epithelium and other cells.

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