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Bioavailability of Folates in Selected Foods Incorporated into Amino Acid-Based Diets Fed to Rats^1,2,

Department of Nutrition ^* Facility for Advanced Instrumentation, University of California, Davis, CA 95616-3376

Two experiments were conducted to determine the feasibility of using a folate depletion/repletion protocol with rats fed an amino acid-based diet to measure the bioavailability of food folate. Growth, liver folate and serum folate of depleted rats that were fed test foods incorporated into a folate-free, amino acid-based diet were standardized against similar responses of rats fed known amounts of folic acid incorporated into the same diet. Bioavailability of folate of cooked broccoli, refried beans and orange juice concentrate in experiment 1 was 80–89, 113 and 62%, respectively, based on growth response; in experiment 2, values for cooked and raw broccoli, cooked cabbage and cantaloupe were 95, 103, 74 and 81%, respectively. The results demonstrate that in addition to serum and liver folate concentrations, growth may be a useful response criterion to evaluate the bioavailability of folates in foods. Further research is needed to determine the relevance of these bioavailability estimates to human nutrition.

KEY WORDS: • folate • bioavailability • rats • amino acid diets

¹ Presented in part at the 73rd annual meeting of the Federation of American Societies for Experimental Biology, New Orleans, LA, March, 1989 [CLIFFORD, A. J., WILSON, D. S., CASEY, S. M., STEDMAN, L. J. & BILLS, N. D. (1989) A rat bioassay of the comparative availability of food folates. FASEB J. 3: A667 (abs.)]. The bioavailability results in that abstract are incorrect because of inaccurate food folate values.

² Supported by USPHS DK-38637 and AM-16726, USDA-CRGO-78-59-2063-0-1-065-1, USDA Regional Research W143 and Hatch 2850 from the California Agricultural Experiment Station.

³ Send correspondence to Dr. Andrew J. Clifford, Department of Nutrition, University of California, Davis, CA 95616.

Manuscript received 13 September 1989. Revision accepted 20 July 1990.