Bioavailability of food folates is 80% of that of folic acid

Background: The bioavailability of natural food folates is lower than that of synthetic folic acid, but no agreement exists as to the extent of the difference. Objective: In a 4-wk dietary intervention study, we determined the aggregate bioavailability of food folates from fruit, vegetables, and liver relative to that of folic acid. Design: Seventy-two healthy adults were randomly divided into 4 treatment groups. Group A (n = 29) received a high-folate diet with 369 μg food folate/d and a placebo capsule; groups B, C, and D (n = 14 or 15) received a low-folate diet with 73 μg food folate/d and folic acid capsules. These capsules contained 92 μg folic acid/d for group B, 191 μg for group C, and 289 μg for group D. In addition, all 72 subjects daily ingested a capsule with 58 μg [¹³C₁₁]-labeled folic acid. We measured the percentage of [¹³C₁₁]-labeled folate in plasma folate at the end of the intervention and ascertained the changes in serum folate concentrations over the 4 wk of the intervention. Results: Bioavailability of food folate relative to that of folic acid was 78% (95% CI: 48%, 108%) according to [¹³C₁₁]-labeled folate and 85% (52%, 118%) according to changes in serum folate concentrations. Conclusions: The aggregate bioavailability of folates from fruit, vegetables, and liver is ≈80% of that of folic acid. The consumption of a diet rich in food folate can improve the folate status of a population more efficiently than is generally assumed.