Subject dietary reference intake

LRNI, Lower Reference Nutrient Intake RNI, Reference Nutrient Intake Al, Adequate Intake RDA, Recommended Dietary Allowance. Sources UK Department of Health (1991) Dietary Reference Values for Food Energy and Nutrients for the United Kingdom, Report on Health and Social Subjects No. 41. London HMSO. USA Food and Nutrition Board, Institute of Medicine (2000) Dietary Reference Intakes for Vitamin C, Vitamin E, Selenium and Carotenoids. Washington, DC National Academy Press. WHO/FAO WHO/FAO (2002) Human Vitamin and Mineral Requirements. Report of a Joint FAO/WHO Expert Consultation, Bangkok, Thailand. Rome WHO/ FAO. 

Figure 1.3. Derivation of reference intake [Recommended Dietary (or Daily) Amount (RDA)], and tolerable upper level (UL) for a nutrient. Curve shows the probability that a subject will show signs of deficiency (left) or toxicity (right) at any given level of intake.

The depletion/repletion studies of Horwitt et al. (1956) and others have suggested, on the basis of restoration of urinary excretion of -methyl nicotinamide, that the average niacin requirement is 5.5 mg per 1,000 kcal (1.3 mg per MJ). Allowing for individual variation, reference intakes (see Table 8.2) are set at 6.6 mg niacin equivalents (preformed niacin - -1 /60 of the dietary tryptophan) per 1,000 kcal (1.6 mgper MJ). Even when energy intakes are very low, it must be assumed that energy expenditure will not fall below 2,000 kcal, and this is the basis for the calculation of reference intakes for subjects with low energy intakes. 

More recent depletion/repletion studies, using more sensitive indices of status in which subjects were repleted with either a constant intake of vitamin Be and varying amounts of protein, or a constant amount of protein and varying amounts of vitamin Bg, have shown average requirements of 15 to 16 /xg per g of dietary protein, suggesting a reference intake of 18... 

It is difficult to determine requirements for dietary vitamin D, as the major source is synthesis in the skin. The main criterion of adequacy is the plasma concentration of calcidiol. In elderly subjects with little sunlight exposure, a dietary intake of 10 fg of vitamin D per day results in a plasma calcidiol concentration of 20 nmol/L, the lower end of the reference range for younger adults at the end of winter. Therefore, the reference intake for the elderly is 10 Jg/day. Average intakes of vitamin D are less than 4 Jg/day, so to achieve an intake of 10 Xg/day will almost certainly require either fortification of foods or the use of vitamin D supplements. 

Chromium(III) is an essential nutrient required for normal energy metabolism. The National Research Council (NRC) recommends a dietary intake of 50-200 ig/day (NRC 1989). The biologically active form of an organic chromium(ni) complex, often referred to as GTF, is believed to function by facilitating the interaction of insulin with its cellular receptor sites. The exact mechanism of this interaction is not known (Anderson 1981 Evans 1989). Studies have shown that chromium supplementation in deficient and marginally deficient subjects can result in improved glucose, protein, and lipid metabolism. 

Overweight/obese subjects show lower concentrations of nutrients than normal weight subjects due to insufficient dietary intake or altered absorption, distribution and metabolism of micronutrients. In our study, obese subjects vitamin B12 values were below the reference interval (only 7%) and holoTC levels below cut-off (only 21 %), perhaps thanks to the Mediterranean diet which redress the imbalance caused by weight, particularly in young subjects. 

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