Chapter 070. Nutritional Requirements and Dietary Assessment (Part 4)

Estimated Average Requirement When florid manifestations of the classic dietary deficiency diseases such as rickets, scurvy, xerophthalmia, and protein-calorie malnutrition were common, nutrient adequacy was inferred from the absence of their clinical signs. Later, it was determined that biochemical and other changes were evident long before the clinical deficiency became apparent. Consequently, criteria of nutrient adequacy are now based on biologic markers when they are available. Priority is given to sensitive biochemical, physiologic, or behavioral tests that reflect early changes in regulatory processes or maintenance of body stores of nutrients. Current definitions focus on the amount of a nutrient...
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Chapter 070. Nutritional Requirements and Dietary Assessment (Part 4) Chapter 070. Nutritional Requirements and Dietary Assessment (Part 4) Estimated Average Requirement When florid manifestations of the classic dietary deficiency diseases suchas rickets, scurvy, xerophthalmia, and protein-calorie malnutrition were common,nutrient adequacy was inferred from the absence of their clinical signs. Later, itwas determined that biochemical and other changes were evident long before theclinical deficiency became apparent. Consequently, criteria of nutrient adequacyare now based on biologic markers when they are available. Priority is given tosensitive biochemical, physiologic, or behavioral tests that reflect early changes inregulatory processes or maintenance of body stores of nutrients. Currentdefinitions focus on the amount of a nutrient that minimizes the risk of chronicdegenerative diseases. The EAR is the amount of a nutrient estimated to be adequate for half ofthe healthy individuals of a specific age and sex. The types of evidence andcriteria used to establish nutrient requirements vary by nutrient, age, andphysiologic group. The EAR is not useful clinically for estimating nutrientadequacy in individuals because it is a median requirement for a group; 50% ofindividuals in a group fall below the requirement and 50% fall above it. Thus, aperson with a usual intake at the EAR has a 50% risk of an inadequate intake. Forthese reasons, other standards, described below, are more useful for clinicalpurposes. Recommended Dietary Allowances The RDA is the nutrient-intake goal for planning diets of individuals; it isused in the MyPyramid food guide of the U.S. Department of Agriculture(USDA), therapeutic diets, and descriptions of the nutritional content of processedfoods and dietary supplements. The nutrient content in a food is stated by weightor as a percentage of the daily value (DV), a variant of the RDA that, for an adult,represents the highest RDA for an adult consuming 2000 kcal/d. The RDA is the average daily dietary intake level that meets the nutrientrequirements of nearly all healthy persons of a specific sex, age, life stage, orphysiologic condition (such as pregnancy or lactation). The RDA is defined statistically as 2 standard deviations (SD) above theEAR to ensure that the needs of most individuals are met. The risk of dietary inadequacy increases as intake falls further below theRDA. However, the RDA is an overly generous criterion for evaluating nutrientadequacy. For example, by definition the RDA exceeds the actual requirements ofall but about 2 to 3% of the population. Therefore, many people whose intake fallsbelow the RDA may still be getting enough of the nutrient. Adequate Intake It is not possible to set an RDA for some nutrients that do not have anestablished EAR. In this circumstance, the AI is based on observed, orexperimentally determined, approximations of nutrient intakes in healthy people.In the DRIs established to date, AIs rather than RDAs are proposed for infants upto age 1 year, as well as for calcium, chromium, vitamin D, fluoride, manganese,pantothenic acid, biotin, choline, sodium, chloride, potassium, and water forpersons of all ages. Tolerable Upper Levels of Nutrient Intake Healthy individuals derive no established benefit from consuming nutrientlevels above the RDA or AI. Excessive nutrient intake can disturb body functionsand cause acute, progressive, or permanent disabilities. The tolerable UL is thehighest level of chronic nutrient intake (usually daily) that is unlikely to pose arisk of adverse health effects for most of the population. Data on the adverseeffects of large amounts of many nutrients are unavailable or too limited toestablish a UL. Therefore, the lack of a UL does not mean that the risk of adverseeffects from high intake is nonexistent. Individual nutrients in foods that mostpeople eat rarely reach levels that exceed the UL. However, nutritionalsupplements provide more concentrated amounts of nutrients per dose and, as aresult, pose a greater potential risk of toxicity. Nutrient supplements are labeledwith Supplement Facts that express the amount of nutrient in absolute units or asthe percent of the DV provided per recommended serving size. Total nutrientconsumption, including both food and supplements, should not exceed RDAlevels.[newpage] Factors Altering Nutrient Needs The DRIs are affected by age, sex, rate of growth, pregnancy, lactation,physical activity, composition of diet, coexisting diseases, and drugs. When onlyslight differences exist between the requirements for nutrient sufficiency andexcess, dietary planning becomes more difficult.