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Nutrient Requirements

A Long-Term Controlled Folate Feeding Study in Young Women Supports the Validity of the 1.7 Multiplier in the Dietary Folate Equivalency Equation¹

Tai Li Yang, Jean Hung^*, Marie A. Caudill², Tania F. Urrutia, Aaron Alamilla, Cydne A. Perry, Rui Li, Hiroko Hata and Edward A. Cogger^**

Human Nutrition and Food Science Department, ^* Kinesiology and Health Promotion Department, Biological Sciences Department, and ^** Animal and Veterinary Science Department, California Polytechnic University, Pomona, CA 91768

²To whom correspondence should be addressed. E-mail: macaudill{at}csupomona.edu.

The presence of folic acid in enriched cereal grain products and the higher bioavailability of folic acid than food folate led to the expression of the 1998 folate RDA, 400 µg/d, as dietary folate equivalents (DFE). DFE are defined as: µg natural food folate + 1.7 x µg synthetic folic acid. The 1.7 multiplier was based on assumptions that added folic acid was 85% available and food folate was 50% available. The 85/50 ratio also inferred that the bioavailability of food folate was 60% relative to added folic acid. The objective of this long-term controlled feeding study was to assess the dietary folate equivalency of folic acid. After a 2-wk period of folate restriction, women (n = 42, 18–45 y old) consumed either 400 or 800 µg DFE/d derived from various combinations of food folate and folic acid for 12 wk. Folic acid was converted to DFE using the 1.7 multiplier from the DFE calculation and was consumed with a meal throughout the treatment period. Folate status response to the various treatments was assessed during wk 12–14. Serum folate, RBC folate, and plasma total homocysteine did not differ among the 400 µg DFE/d groups or among the 800 µg DFE/d groups. In contrast, consumption of 800 µg DFE/d led to higher (P 0.05) serum and RBC folate than consumption of 400 µg DFE/d. These data support the validity of the 1.7 multiplier in the DFE equation and suggest that food folate bioavailability is 60% that of added folic acid when consumed as part of a mixed diet.

KEY WORDS: • folate • bioavailability • folic acid • dietary folate equivalent • DFE

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