In the United States, the National Academy of Sciences, through the National Research Council and The Institute of Medicine, has convened expert groups since 1941 to establish nutrition recommendations to be used by individuals and institutions for planning nutritionally adequate diets. These groups have established recommended dietary allowances (RDAs) as the daily dietary intake level for a specific nutrient that is sufficient to meet the nutritional requirements of nearly all (97–98 percent) individuals in the life stage and gender group specified. In the most recent recommendations, dietary reference intakes (DRIs) have been specified that have attempted to estimate average nutrient requirements, RDAs, and an upper limit of safe nutrient intake. Where data are not sufficient to set a precise RDA, new recommendations called adequate intake (AI) define a recommendation for some nutrients.
The RDAs and AIs are used to plan diets for groups in hospitals, the military, large institutions, to set standards for government food programs such as school lunches, to establish nutritional labeling, and for counseling individuals. Similar dietary recommendations have been made by expert groups convened in many countries and also by international organizations such as the World Health Organization and the Food and Agricultural Organization of the United Nations. These recommendations are periodically revised to include information from most recent research findings. The latest recommendations for dietary reference intakes can be obtained in the United States from the National Academy Press, 2101 Constitution Avenue, NW, Washington, D.C. 20418.
Recommendations have been established for most nutrients where sufficient research data are available to make reliable estimates. The nutrient recommendations are given for different age groups and are differentiated by sexes because of different nutritional needs at different stages of life. Infants and young children who are growing rapidly have different nutrient needs compared to adults. Women who are menstruating need more iron to replace blood lost in the menstruation compared to postmenopausal women or men. Similarly, there are special needs for pregnant and lactating women. There is increasing evidence accumulating about the needs of the elderly, and nutrition recommendations now include a category for individuals over seventy years of age.
Recent revisions of nutrition recommendations have taken into account public health concerns about osteoporosis, a condition in which bone mineral is lost and older individuals become more vulnerable to bone fractures. New recommendations stress the importance of maintaining a high level (1200 mg/day) of calcium intake by both men and women over fifty years of age in an attempt to reduce loss of bone mineral. Similarly, recommendations for folic acid intake have also been revised to stress the importance of sufficient folic acid consumption by women who may become pregnant. Insufficient folic acid has been associated with a higher incidence of birth defects. The concern for adequate intake of folic acid led to the fortification of enriched grain products with folic acid in the United States beginning in 1998.
Nutrient recommendations also take into consideration the efficiency by which nutrients are digested and absorbed from foods. The form in which iron is ingested has a major influence on how much food iron is absorbed into the body. Iron in animal products is well absorbed because it is found as a component of hemoglobin or muscle pigments, while iron in plants, found as inorganic salts, is poorly absorbed. Some components of plants, such as phytic acid and tannins, also interfere with iron absorption. Therefore, dietary recommendations for iron intake must consider the availability of iron in the foods being consumed.
MALDEN C. NESHEIM, The Gale Group Inc., Macmillan Reference USA, New York,