Requirements and Intakes

The most extensive such study was that of Horwitt and coworkers (1956). They found that there was a considerable variation between subjects in the response to tryptophan and niacin, and suggested that in order to allow for individual variation, it should be assumed that 60 mg of tryptophan was equivalent to 1 mg of preformed niacin. This ratio has been generally accepted, and is the basis for expressing niacin requirements and intake in terms of niacin equivalents - the sum of preformed niacin and 1 /60 of the tryptophan. 

There is a growing awareness of the limitations of current approaches to the collection and assessment of dietary data. There is a search for new and better methodology. Alternative approaches to both procedures for data collection and to interpretation of collected data have been presented. These appear to represent a considerable improvement on previous strategies. Careful application of these approaches may enhance the accuracy of estimates of nutrient requirements and intakes. By comparing the situation predicted from dietary analyses with that suggested by biochemical studies, an epidemiologic test of the validity of requirement estimates can be undertaken. The approaches described have both immediate operational application and future research implication. 

Wiss and co-workers (1964) (44) as well as Weber and Weiser (1967) (45) clarified the relationship between vitamin E requirement and intake of linoleic acid by the hemolysis test. According to these authors man needs 0.5 to 1.0 mg vitamin E per gram linoleic acid to compensate for the increased requirement of vitamin E due to higher polyenic acid content in such diets. Only therefore and not for ailing and healthy hearts" can a daily intake of 10-15 mg vitamin E be recommended. 

Pumps, compressors, turbines, drivers, and auxiliary machinery should be designed to provide reliable, rugged performance. Pump selection and performance depend on the capacity required and tlie nature of Uie fluids involved. Remotely controlled power switches and shutoff valves are necessary to control fluid flow during an emergency. The inlets for air compressors should be strategically located to prevent the intake of hazardous materials. 

Inorganic iron is absorbed only in the (reduced) state, and for that reason the presence of reducing agents will enhance absorption. The most effective compound is vitamin C, and while intakes of 40-60 mg of vitamin C per day are more than adequate to meet requirements, an intake of 25-50 mg per meal will enhance iron absorption, especially when iron salts are used to treat iron deficiency anemia. Ethanol and fructose also enhance iron absorption. Heme iron from meat is absorbed separately and is considerably more available than inorganic iron. However, the absorption of both inorganic and heme iron is impaired by calcium—a glass of milk with a meal significantly reduces availabiUty. 

Routine antioxidant vitamin supplementation, e.g. with vitamins C and/or E, of the diabetic diet should be considered. Vitamin C depletion is present in all diabetics irrespective of the presence of vascular disease. A recent study demonstrated no significant difference between the dietary intake of vitamin C (the main determinant of plasma ascorbate) in patients with diabetes and age-matched controls, confirming the view that ascorbate depletion is secondary to the diabetic process and su esting that diabetic patients require additional intakes of the vitamin to maintain optimal levels (Sinclair et /., 1994). Antioxidant supplementation may have additive beneficial effects on a wide variety of processes involved in diabetic vascular damage including blood pressure, immune function, inflammatory reactions. 

Generation of data on the nutrient content of agricultural products and foods forms the basis for estimating nutrient intakes of populations via dietary surveys, nutritional labelling for consumer protection, nutrition education for consumer food choice, home and institution menu planning and food purchase, and for research in nutrient requirements and metabolism, toxicant chemical composition is used to assess effects of farm management practices, crop culture, and food processing on chemical content and implications for human health. 

Most CF patients have an increased caloric need due to increased energy expenditure through increased work of breathing and increased basal metabolism. Prevention of malnutrition requires early nutritional intervention. In patients with mild lung disease and well-controlled absorption, required caloric intake is approximately 100% to 120% of the recommended daily allowance (RDA) for age.15 As lung disease progresses, caloric requirements increase. 

Calcium is essential for bones, teeth, metabolic signaling and regulation, and other bodily functions. Adults require an intake of around lg per day only about 10% of the calcium ingested is absorbed into the body - less from a low-protein diet, more from a high-protein diet. Vitamin D facilitates absorption, as does... 

Most of the forementioned studies which examined the influence of various dietary fiber on the bioavailability of calcium by human subjects have depended upon the comparative measurements of calcium content of diets and calcium contents of stools and urine. As reviewed by Allen (3), calcium balance studies have distinct limitations relative to accuracy and precision. However, their ease of application and cost, laboratory equipment requirements, and real (or perceived) safety in comparison to available radioactive or stable isotope methods continue to make their use popular. In calcium balance studies, calcium absorption is assumed to be the difference between calcium excretion in the feces and calcium intake. Usually this is expressed as a percent of the calcium intake. This method assumes that all fecal calcium loss is unabsorbed dietary calcium which is, of course, untrue since appreciable amounts of calcium from the body are lost via the intestinal route through the biliary tract. Hence, calcium absorption by this method may underestimate absorption of dietary calcium but is useful for comparative purposes. It has been estimated that bile salts may contribute about 100 g calcium/day to the intestinal calcium contents. Bile salt calcium has been found to be more efficiently absorbed through the intestinal mucosa than is dietary calcium (20) but less so by other investigators (21). 

For the estimation of the magnitude of the potential dose of chemicals from drinking water, information on the quantity of water consumed per unit time is required. The intake of drinking water depends on age, level of physical activity (working, running, walking, or resting), and the ambient temperature. 

Folic acid deficiency, unlike vitamin B12 deficiency, is often caused by inadequate dietary intake of folates. Patients with alcohol dependence and patients with liver disease can develop folic acid deficiency because of poor diet and diminished hepatic storage of folates. Pregnant women and patients with hemolytic anemia have increased folate requirements and may become folic acid-deficient, especially if their diets are marginal. Evidence implicates maternal folic acid deficiency in the occurrence of fetal neural tube defects, eg, spina bifida. (See Folic Acid Supplementation A Public Health Dilemma.) Patients with malabsorption syndromes also frequently develop folic acid deficiency. Patients who require renal dialysis develop folic acid deficiency because folates are removed from the plasma during the dialysis procedure. 

The use of food additive petitions and GRAS procedures to evaluate the safety of a proposed new excipient would apply to the oral route of administration for the excipient and would not generally apply to other routes of administration. Some routes of administration (e.g., inhalation) result in unique toxicological requirements, and data would have to be developed for the specific route of administration. While toxicological data from systemic studies are important for excipients used for nonoral applications, separate data would be needed for the specific route of administration. Nevertheless, the amount of safety data, specifications, and intake information required for a food additive review is extensive, and therefore could provide a firm basis of safety for a new excipient. 

This is known as Michaelis-Menten or saturation kinetics. The processes that involve specific interactions between chemicals and proteins such as plasma protein binding, active excretion from the kidney or liver via transporters, and metabolism catalyzed by enzymes can be saturated. This is because there are a specific number of binding sites that can be fully occupied at higher doses. In some cases, cofactors are required, and their concentration may be limiting (see chap. 7 for salicylate, paracetamol toxicity). These all lead to an increase in the free concentration of the chemical. Some drugs, such as phenytoin, exhibit saturation of metabolism and therefore nonlinear kinetics at therapeutic doses. Alcohol metabolism is also saturated at even normal levels of intake. Under these circumstances, the rate of... 

Dietary requirements for AAs and protein usually are stated as proportions of the diet. However, the level of feed consumption has to be taken into account to ensure that the total intake of protein and AAs is appropriate. The protein and AA requirements derived by the NRC (1994) relate to poultry kept in moderate temperatures (18-24°C). Ambient temperatures outside of this range cause an inverse response in feed consumption i.e. the lower the temperature, the greater is the feed intake and vice versa (NRC, 1994). Consequently, the dietary levels of protein and AAs to meet the requirements should be increased in warmer environments and decreased in cooler environments, in accordance with expected differences in feed intake. These adjustments are designed to help ensure the required daily intake of AAs. 

However, the effect of piperine on SULT and flavonoid status across the life cycle remains to be investigated. Induction of phase II metabolism appears to decrease the bioavailability and accelerate the excretion of flavonoids. For example, Siess et al.115 and Walle et al.116 reported flavones induced rat hepatic UGT activity in HepG2 and Caco-2 cells. This induction of UGT enhanced quercetin glucuronidation in Caco-2 cells. In addition to inducing UGT activity, the flavone chrysin inhibits hepatic SULT-mediated sulfation of acetaminophen and minoxidol." The impact of chrysin on the capacity of COMT action toward flavonoids has not been examined. Further, the effect of age on phase II modulation by piperine and chrysin has not been reported. Thus, information on the relationship between age and intake of flavonoids and other phytochemicals that also affect phase II metabolism is required. 

XI. Selenium Requirements and Recommended Dietary Intakes XII. Summary and Conclusions References... 

Yang, G. and Xia, Y. 1995. Studies on human dietary requirements and safe range of dietary intakes of selenium in China and their application in the prevention of related endemic diseases. Biomed. Environ. Sci. 8, 187-201. 

Iron is another essential metal that can overload the body as a result of genetic disorders. Hereditary hemochromatosis and sub-Saharan African hemochromatosis are two examples. These two disorders differ in that hereditary hemochromatosis results in excessive iron when iron intake levels are normal, while sub-Saharan African hemochromatosis requires excessive intake of Fe coupled with a genetic predisposition to poorly regulate iron. Generally speaking, toxicity associated with excess essential metals tends to be rare, and it most frequently occurs in people who inappropriately consume dietary supplements. 

There is no evidence for any toxic effects of chromium(III), which is an essential trace element in mammals (required daily intake 50-200 /tg) and participates in glucose and lipid metabolism. In the low-molecular-weight Cr binding substance (LMWCr), an oligopeptide, a tetranuclear Crm carboxylate complex may be present.44... 

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