The determination of requirements and reference intakes

For any nutrient, there is a range of intakes between that which is clearly inadequate, leading to clinical deficiency disease, and that which is so much in excess of the body s metabolic capacity that there may be signs of toxicity. Between these two extremes is a level of intake that is adequate for normal health and the maintenance of metabolic integrity and a series of more precisely definable levels of intake that are adequate to meet specific criteria and may be used to determine requirements and appropriate levels of intake  

1 A3) may reduce the risk of developing cardiovascular disease and some forms of cancer. High intakes of folate during early pregnancy reduce the risk of neural tube defects in the fetus (section 11.11.5.1). 

Having decided on an appropriate criterion of adequacy, requirements are determined by feeding volunteers a diet that is an otherwise adequate but lacks the nutrient under investigation until there is a detectable metabolic or other abnormality. The volunteers are then repleted with graded intakes of the nutrient until the abnormality is just corrected. 

Problems arise in interpreting the results, and therefore defining requirements, when different markers of adequacy respond to different levels of intake. This explains the difference in the tables of reference intakes published by different national and international authorities (see Tables 11.1-11.3). 

Individuals do not all have the same requirement for nutrients, even when calculated on the basis of body size or energy expenditure. There is a range of individual requirements of up to 25% around the average. Therefore, in order to set population goals, and assess the adequacy of diets, it is necessary to set a reference level of intake that is high enough to ensure that no-one will either suffer from deficiency or be at risk of toxicity. 

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