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Manuscript received 13 March 1998. Initial reviews completed 13 May 1998. Revision accepted 24 June 1998.
Food Science and Human Nutrition Department, University of Florida, Gainesville, FL 32611-0370
In a 10-wk study of folate metabolism in nonpregnant women (21-27 y, n -6 per group), subjects were fed a diet containing ~68 nmol/d (30 µg/d) folate from food. The remainder of the ingested folate was provided as folic acid in apple juice (as nonlabeled during wk 1-2, as [2H2]folic acid during wk 3-10) to yield a constant intake of 454, 680 or 907 nmol/d (200, 300 or 400 µg/d). Isotopic enrichment of total urinary folate and the primary catabolite para-acetamidobenzoylglutamate (ApABG) was determined. Isotopic enrichment of ApABG served as an indicator of labeling of tissue folates. A kinetic model consisting of fast- and slow-turnover nonsaturable pools and a saturable slow-turnover pool, with provisions for urinary and fecal excretion, catabolism and enterohepatic circulation, yielded a close fit to the data. Mean residence times for total body folate were 212, 169 and 124 d for folate intakes of 454, 680, and 907 nmol/d, respectively. The model predicted that variation in folate intake over this range had little effect on the mass of the large saturable folate pool; however, the fast-turnover nonsaturable pools increased in proportion to folate intake, whereas the slow nonsaturable pool also tended to increase. This model will aid in evaluation of folate turnover and in predicting kinetic consequences of physiologic conditions associated with altered folate requirements.
Key words: folate, kinetics, modeling, requirements, stable isotopes, humans.
The Journal of Nutrition Vol. 128 No. 11 November 1998,
pp. 1896-1906
Copyright ©1998 by the American Society for Nutritional Sciences
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