Part of “CHAPTER 124 – PRINCIPLES OF NUTRITIONAL MANAGEMENT“

The provision of essential nutrients to humans in correct amounts is necessary for both the maintenance of existing tissues and the generation of new tissues. Required nutrients include nitrogen, several minerals, and an appropriate and adequate source of energy. Because their biosynthetic pathways are lacking or inadequate, essential amino acids, two fatty acids, and vitamins must be included in the diet. Recommended dietary allowances (RDAs), published by the National Research Council, have defined requirements for energy, protein, vitamins, and minerals, as well as general recommendations for intake of carbohydrate, fiber, and lipids in healthy Americans.1 The National Academy of Sciences has begun to report dietary reference intakes (DRIs) for nutrients, which eventually will replace the old RDAs.2 DRIs encompass two standards that can be used to assess the intake of individuals (RDAs and adequate intakes [AIs]) and one that can be used to assess the intake of groups (estimated average requirements [EARs]). In addition to more traditional parameters of sufficient nutrient intake, DRIs take into consideration evidence concerning the role of nutrients in the prevention of disease and developmental disorders. Currently DRIs are available for calcium, phosphorus, magnesium, vitamin D, fluoride, thiamine, riboÿavin, niacin, vitamin B₆, folate, vitamin B₁₂, pantothenic acid, biotin, choline, vitamin C, vitamin E, selenium, and carotenoids. These values establish for the first time upper limits for nutrient consumption. The upper limit is defined as the maximal level of nutrient intake that is unlikely to pose risks of adverse health effects in almost all individuals. In considering the established requirements for nutrients, it is important to appreciate that nutritional requirements can be altered by endocrinologic and metabolic disorders. Conversely, certain types of nutritional support, such as parenteral hyperalimentation, can cause endocrinologic or metabolic disease. For these reasons, optimal patient care requires a knowledge of normal nutritional requirements and of the relations between nutrition and disease.