Food Sources of Folate

Folate is synthesized by microorganisms and higher plants but not by mammals, for which it is an essential vitamin. The most concentrated food folate sources include liver, yeast extract, green leafy vegetables, legumes, certain fruits, and fortified breakfast cereals. Folate content is likely to depend on the maturity and variety of particular sources. Foods that contain a high concentration of folate are not necessarily those that contribute most to the overall intakes of the vitamin in a population. For example, liver is a particularly concentrated source, providing 320 mg of folate per 100 g, but it is not eaten by a sufficient proportion of the population to make any major contribution to total dietary folate intakes. The potato, on the other hand, although not particularly rich in folate, is considered a major contributor to folate in the UK diet, accounting for 14% of total folate intake because of its high consumption. Prolonged exposure to heat, air, or ultraviolet light is known to inactivate the vitamin; thus, food

Table 3 Contributions of the main food groups to the average daily intake of folate in British and US adults (%)

Food group

USA (1994)

UK (1998)

Dairy products

8.1

9.8

Meat, poultry, fish

8.5

6.5

Grain products

21.2a

31.8

Fruit, fruit juices

10.2

6.9

Vegetables

26.4

31.8

Legumes, nuts, soy

18.5

Eggs

5.1

2.4

Tea

4.1

Other food

2.1

5.7

aPrior to mandatory fortification of flour-based products.

preparation and cooking can make a difference to the amount of folate ingested; boiling in particular results in substantial food losses. The major source of folate loss from vegetables during boiling may be leaching as opposed to folate degradation. Broccoli and spinach are particularly susceptible to loss through leaching during boiling compared with potatoes because of their larger surface areas. The retention of folate during cooking depends on the food in question as well as the method of cooking. Folates of animal origin are stable during cooking by frying or grilling. In addition to highlighting good food sources, public-health measures promoting higher folate intake should include practical advice on cooking. For example, steaming in preference to boiling is likely to double the amount of folate consumed from green vegetables.

While cultural differences and local eating habits determine the contribution of different foodstuffs to folate intake (Table 3), as with other nutrients, globalization and the integration of the international food industry may lead to more predictable 'Westernized' diets in the developed and developing world. Internationally, much of the dietary folate in the 'Western' diet currently comes from fortified breakfast cereals, though this foodstuff is likely to be joined shortly in this regard by fortified flour products in the light of the experience of the US food fortification program. In the main, though, adherence to dietary recommendations to increase the consumption of folate-rich foods is likely to enhance the intake not only of folate but also of other nutrients essential to health.

See also: Adolescents: Nutritional Requirements. Amino Acids: Chemistry and Classification; Metabolism; Specific Functions. Anemia: Megaloblastic Anemia. Breast Feeding. Cobalamins. Food Fortification: Developed Countries; Developing Countries. Fruits and Vegetables. Infants: Nutritional Requirements. Lactation: Physiology; Dietary Requirements. Pregnancy: Safe Diet for Pregnancy; Prevention of Neural Tube Defects.

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