Dietary allowance

As for other biological substances, states of dynamic equiUbrium exist for the various mineral nutrients as well as mechanisms whereby a system can adjust to varying amounts of these minerals in the diet. In forms usually found in foods, and under circumstances of normal human metaboHsm, most nutrient minerals are not toxic when ingested orally. Amounts considerably greater than the recommended dietary allowances (RDAs) can generally be eaten without concern for safety (Table 1) (3). 

Because there is less information upon which to base dietary allowances for biotin and pantothenic acid, ranges of intake are provided, as in Table 8. 

Committee on Dietary Allowances, Eood and Nutrition Board, Kecommended Dietary Allowances, 10th ed.. National Academy of Sciences, Washington, D.C., 1989, pp. 115-124. 

The amount of foHc acid required for daily iatake is estimated based oa the minimum amouat required to maintain a certaia level of semm folate. The recommeaded dietary allowance (RDA) for foHc acid accounts for daily losses and makes allowances for variation ia iadividual aeeds and bioavailabiUty from food sources (85). The U.S. recommended daily allowance for adults is 400 p.g and for pregnant women is 800 ]1 (Table 4). 

Pantothenic acid is widely distributed in food and because of the lack of conclusive evidence regarding quantitative needs, a recommended dietary allowance (RDA) for pantothenic acid has not been estabUshed. In 1989, the Food and Nutrition Board of the United States National Research Council suggested a safe intake of 4—7 mg/d for adults. The provisional allowance for infants is 2—3 mg daily (90). 

Recommended Dietary Allowances 7di ed.. National Academy of Science, National Research Council, Washiagton, D.C., 1968, p. 1964. 

Table 2 Hsts the Recommended Dietary Allowances (RDA) for vitamin K. Although manufacture by intestinal bacteria represents a significant source of plasma menaquinone concentrations, rehance on this source alone is not sufficient to maintain healthy concentrations of menaquinone. Consequendy, dietary supplementation is necessary (76).

Vitamin C occurs as L-ascorbic acid and dihydroascorbic acid in fruits, vegetables and potatoes, as well as in processed foods to which it has been added as an antioxidant. The only wholly undisputed function of vitamin C is the prevention of scurvy. Although this is the physiological rationale for the currently recommended intake levels, there is growing evidence that vitamin C may provide additional protective effects against other diseases including cancer, and the recommended dietary allowance (RDA) may be increased in the near future. Scurvy develops in adults whose habitual intake of vitamin C falls below 1 mg/d, and under experimental conditions 10 mg/d is sufficient to prevent or alleviate symptoms (Bartley et al., 1953). The RDA is 60 mg per day in the USA, but plasma levels of ascorbate do not achieve saturation until daily intakes reach around 100 mg (Bates et al., 1979). Most of the ascorbate in human diets is derived from natural sources, and consumers who eat five portions, or about 400-500 g, of fruits and vegetables per day could obtain as much as 200 mg of ascorbate. 

NAS-NRC, Recommended Dietary Allowances, National Academy of Science, Washington, 1989, 78. 

Polymeric formulas typically have low osmolality of 300 to 500 mOsm/kg. These formulas also usually supply essential vitamins and minerals in amounts similar to the Adequate Intakes or Recommended Dietary Allowances for these nutrients when the formula is delivered in amounts adequate to meet the macronutrient requirements of most patients. Many polymeric formulas are inexpensive relative to oligomeric formulas. Most polymeric formulas are lactose-free and gluten-free, as are most modern tube feeding products. Products designed to be used as oral supplements generally are polymeric and often have sucrose or other simple sugars added to improve taste. 

No significant quantity of the macronutrients nor of the vitamins for which U.S. Recommended Dietary Allowance (RDA) have been established can be obtained from the consumption of a cup of tea.110 The water-soluble B vitamins present are easily extractable. Eight percent extractabil-ity for a representative black tea blend is assumed.110... 

Nutritional surveys indicate that children of low-income groups consume less than recommended dietary allowances of calcium and iron. Dietary deficiencies of these two minerals have been shown to potentiate the toxicity of lead (Johnson and Tenuta 1979 Yip et al. 1981 Ziegler et al. 1978). Thus, nutrient deficiencies in conjunction with a developmental predisposition to absorb lead makes this subset of children at a substantially elevated risk. More information on children s susceptibility to lead is presented in Section 2.6. 

Humans given zinc supplements should be aware of possible complications (Fosmire 1990). Low intakes of 100 to 300 mg of zinc daily in excess of the recommended dietary allowance of 15 mg Zn daily may produce induced copper deficiency, impaired immune function, and disrupted blood lipid profiles. Patients treated with zinc supplements (150 mg daily) to control sickle cell anemia and nonresponsive celiac disease developed a severe copper deficiency in 13 to 23 months normal copper status was restored by cessation of zinc supplements and increased dietary copper (Fosmire 1990). 

To replace recommended dietary allowances, the Food and Nutrition Board created the dietary reference intakes made up of seven nutrient groups. 

F, female M, male RDA, recommended dietary allowance. 0 Adequate intake. 

Recommended Dietary Allowance (RDA), 17 652 25 784-787 of ascorbic acid, 25 772 defined, 25 784 for vitamins, 25 785t Recommended exposure level (REL), hydrazine, 13 590... 

A healthy diet with proper nutrition is essential for maintaining good overall health. Since the discovery of vitamins earlier in this century, people have routinely been taking vitamin supplements for this purpose. The Recommended Dietary Allowance (RDA) is a frequently used nutritional standard for maintaining optimal health. The RDA specifies the recommended amount of a number of nutrients for people in different age and sex groups. The National Research Council s Committee on Diet and Health has proposed a definition of the RDA to be that amount of a nutrient which meets the needs of 98% of the population. 

Dietary intake data for calcium, phytate and phytate/calcium ratio are summarized in Table II. Mean calcium intake for HS-I was about 300 mg greater than the recommended dietary allowance (RDA) of 800 mg established for adults by the National Research Council (8) and for HS-II just slightly less than the RDA. The range of calcium intakes, because of different caloric needs was from 927 to 1490... 

National Research Council "Recommended Dietary Allowances", National Academy of Sciences, Washington, DC, 1980. 

In the studies on humans there appeared to be decreased calcium balances when 200 g or more of spinach per day was included in the diet. In two of the studies in which women were fed spinach, calcium intakes were below the Recommended Dietary Allowance of 800 mg/day (37). Some studies were conducted for short period of a week or less, which may not be sufficient time to adjust to a change in diet. From measurement of calcium excretion in urine after a test meal, it was shown that the calcium in oxalate-containing vegetables was less well-absorbed than that of milk or of vegetables not containing oxalic acid. However, this would not necessarily affect calcium balance, since the total amount of calcium in the diet would have to be considered. The effect of a combination of oxalic acid and fiber on calcium bioavailability should be further investigated. 

Recommended Dietary Allowances," National Academy of Sciences, 1980, 9th ed. 

It has been well established that the ingestion of high dietary protein levels results in hypercalciuria in man, and that hypercalciuria is frequently accompanied by negative calcium balance (1-3). In a summary of data from nutritional surveys in the U.S., Pao (4J showed that dietary protein intake was well above the Recommended Dietary Allowances (RDA) for both men and women regardless of age (1). Although dietary calcium intakes are generally at the RDA for men, women below the age of 50 yr consume only 75% of the RDA (4J. Women above the age of 50 yr consume only two-thirds of the RDA for calcium (4). These low consumptions become critical when we consider the reduced ability for calcium absorption demonstrated in both men and women over the age of 60 yr (6). 

The recommended dietary allowance, RDA, for calcium In the United States Is 800 mg per day (1) However, this amount of calcium may not be adequate throughout adult life for maintaining the normal skeletal structure and for preventing bone loss with aging, particularly In females Recent studies Indicate that this amount of calcium may not be adequate for maintaining the optimal bone mass which reaches Its peak at the age of 30 to 35 years (2) and decreases thereafter Even If the calcium Intake Is adequate, one has to consider to which extent this amount of calcium Is utilized There may be a decrease In the Intestinal absorption of calcium (3) or the... 

The concept of biochemical individuality has become part of most contemporary clinical and experimental medical and nutritional research. People are now known to fit into personally unique biochemical profiles based upon their own genetic structure, nutrition and environment.5 There is no such thing as a truly "normal" individualmeaning average. We are all biochemically unique and need to be dealt with as such. The Recommended Dietary Allowances (RDAs) which were developed by the Food and Nutrition Board of the National Research Council to establish the nutritional needs of "practically all healthy people" were not based upon the more recent information concerning the range of biochemical individuality among individuals. The RDAs that describe "normal" nutritional needs have questionable relevancy to the concept of optimal nutrition based upon individual needs. The contributions of Dr. Williams have opened the door for personally tailored nutritional and medical interventions that take biochemical individuality into account. 

Recommended Dietary Allowances, National Academy of Sciences, National Research Council, Washington, D. C., Publication 302 (rev ), 1953, p. 10. 

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