Dietary folate equivalent

By contrast, dietary deficiency of vitamin B12 is rare, except among strict vegetarians, despite the fact that the vitamin is found only in animal foods and some bacteria rather, pernicious anemia caused by vitamin B12 lack is normally the result of a defect in the mechanism for intestinal absorption of the vitamin. 

In the folate coenzymes, the pteridine ring is fully reduced to tetrahydro-folate, although the oxidized form, dihydrofolate, is an important metabolic intermediate. In the reactions of thymidylate synthetase (Section 10.3.3) and methylene tetrahydrofolate reductase (Section 10.3.2.1), the pteridine ring has a redox role in the reaction. The folate coenzymes are conjugated with up to six additional glutamate residues, finked by y-glutamyl peptide bonds. 

Although the terms folic acid and folate are often used interchangeably, correctly/ofic acid refers to the oxidized compound, pteroyl monoglutamate, and the various tetrahydrofolate derivatives are collectively known as folates. 

5-Formyl-tetrahydrofolate is more stable to atmospheric oxidation than folic acid itself and is commonly used in pharmaceutical preparations it is also known as folinic acid and the synthetic (racemic) compound as leucov-orin. Although the [6S, 67 ] racemic mixture might be expected to have only 50% of the biological activity of the naturally occurring 6S isomer, between 10% to 40% of the 67 isomer is biologically active (Baggott et al., 2001). 

The folate in foods consists of a mixture of the different one-carbon substituted derivatives, with varying numbers of conjugated glutamyl residues. The biological availability of these vitamers differs and is consistently lower than that of free folic acid (pteroyl monoglutamate), which is the compound that 

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Based on folate concentrations in liver biopsy samples, and assuming that the liver contains about half of ail body stores, total body stores of folate are estimated to be between 12 and 28 Kinetic studies that show both fast-turnover and very-slow-turnover folate pools indicate that about 0.5% to 1% of body stores are catabolized or excreted daily,suggesting a minimum daily requirement of between 60 and 280)Llg to replace losses. In calculating nutritional requirement, the concept of dietary folate equivalents (DFE) has been used to adjust for the nearly 50% lower bioavailabihty of food folate compared with supplemental folic acid, such that 1 p.g DFE = 0.6 Llg of folic acid from fortified food = 1 j,g of food folate 0.5 p.g foUc acid supplement taken on an empty stomach. Before the fortification program of cereal grains with folic acid conducted between 1988 and 1994, the median intake of folate from food in the United States was approximately 250p.g/day this figure is expected to increase by about 100 Llg/day after fortification. Recommendations... 

As dietary folate equivalents (DFE). 1 DFE = 1 pg food folate = 0.6 pg of folic acid from fortified food or as a supplement consumed with food = 0.5 pg of a supplement taken on an empty stomach... 

Table 44.2 Folate dietary reference intakes according to the age in mg Dietary Folate Equivalents (DFE/day). ...

The extent to which the different forms of folate can be absorbed varies in order to permit calculation of folate intakes, the dietary folate equivalent has been defined as 1 Ig mixed food folates or 0.6 ig free folic acid. On this basis, total dietary folate equivalents = Ig food folate + 1.7 X synthetic (free) folic acid. 

The 1998 recommendations for folate are expressed using a term called the dietary folate equivalent (DFE). The DFE was developed to help account for the difference in bioavailability between naturally occurring dietary folate and synthetic folic acid. The Food and Nutrition Board of the US National Academy of Sciences reasoned that, since folic acid in supplements or in fortified food is 85% bioavailable, but food folate is only about 50% bioavailable, folic acid taken as supplements or in fortified food is 85/50 (i.e., 1.7) times more available. Thus, the calculation of the DFE for a mixture of synthetic folic acid and food is pg of DFE = pg food folate + (1.7 x pg synthetic folate). 

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