How Should the Recommended Dietary Allowances be Revised? (1994) / Chapter Skim
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2 CONCEPTS UNDERLYING THE RECOMMENDED DAILY ALLOWANCES
2 CONCEPTS UNDERLYING THE RECOMMENDED DAILY ALLOWANCES
Pages 7-16
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From page 7... ...
During World War I, the Food Committee of the British Royal Society developed a report on food requirements based on existing knowledge of nutritional needs (Cruikshank, 1946~. Between 1925 and 1937, the Health Organization of the League of Nations published a series of documents examining aspects of food and nutrition problems, culminating in a report on estimated requirements for vitamin and mineral intake (Harper, 1987~.
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From page 8... ...
All RDA committees rely heavily on published literature. Recent RDA committees have sought additional scientific expertise through correspondence, workshops, and special meetings with invited experts.
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From page 9... ...
In addition, the values for each nutrient above the minimal level which will prevent deficiency are considered to provide for increased needs in times of stress and to permit other potential benefits. Although the optimal intake of essential dietary constituents remains largely speculative, there is considerable evidence that improvement in growth and function occurs when the intake of certain nutrients is increased above the level just sufficient to prevent signs of deficiency disease (NRC, 1953, pp.
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From page 10... ...
The FNB adopted the term "recommended dietary allowances" to avoid any implication of finality or that the allowances represented minimal or optimal requirements. Studies with animals indicated that the amounts of some nutrients sufficient to provide health for short portions of the life span might be inadequate to maintain good health throughout life (NRC, 1948~.
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From page 11... ...
Six types of evidence are used in establishing RDAs: · nutrient intakes observed in apparently normal, healthy people, · epidemiological observations of populations in which the clinical consequences of nutrient deficiencies are corrected by dietary improvement, · balance studies that measure nutrient status in relation to intake, · nutrient depletion/repletion studies in which subjects are maintained on diets containing marginally low or deficient levels of a nutrient, followed by correction of the deficit with measured amounts of that nutrient (such studies are undertaken in humans only when the risk is minimal) , · extrapolation from animal experiments, and · biochemical measurements that assess the degree of tissue saturation or adequacy of molecular function in relation to nutrient intake.
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From page 12... ...
PHARMACOLOGICAL EFFECTS Recent RDA committees have commented on the use of nutrients at levels many times the RDA to attain health effects unrelated to the functional roles associated with levels achievable through dietary means alone. Some examples of these pharmacological effects include nicotinic acid, which when taken in doses of up to 9 grams daily, reduces serum lipids; vitamin A analogues, which are used to treat skin disorders; and antioxidant nutrients such as vitamins C and E, which some epidemiological data suggest may reduce the risk of coronary heart disease.
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From page 13... ...
Recognizing that diets high in polyunsaturated fatty acids reduce plasma cholesterol levels in hypercholes
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From page 14... ...
In the 1974 edition, the committee concluded that individuals at risk of coronary heart disease should adopt dietary modifications to lower their serum cholesterol concentrations. It recommended that individuals follow what was then the American Heart Association's recommendations to reduce dietary fat to 35 percent of kcal derived from fat, of which less than 10 percent should come from saturated fatty acids, no more than 10 percent from polyunsaturated fatty acids, and the remainder from monounsaturated fatty acids.
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From page 15... ...
Among them are central questions about what the RDAs are meant to be: Are they levels of intake based on requirements for specific biochemical functions? Are they based on less specific physiological outcomes possibly related to multiple functions?
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