A long-term controlled folate feeding study in young women supports the validity of the 1.7 multiplier in the dietary folate equivalency equation

Abstract

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. © 2005 American Society for Nutritional Sciences.