Establishing Nutrient Intake Requirements

Oral nutrient intake requirements for infants have been established from (1) analysis of body composition (2) direct clinical studies on various feeding regimens or (3) analysis of the nutrient content of mature human milk. There are, however, marked differences between intravenous and oral requirements. For example, when determining oral requirements, the various factors affecting nutrient utilization, such as bioavailability and rates of absorption, have to be considered (Fomon et aL, 1977). 

Optimal dietary intake is difficult to determine. Dietary Reference Intakes (DRIs) in the US are reference values that are quantitative estimates of nutrient intakes to be used for planning and assessing diets for apparently healthy people. DRIs are composed of reference values including Estimated Average Requirements (EARs), Recoimnended Dietary Allowances (RDAs), Adequate Intakes (AIs) and Tolerable Upper Intake Levels (ULs). Most nations have established the eqnivalent ofthe US DRIs. These are consensus and statistical valnes obtained from retrospective public health dietary studies, controlled experiments on metabolic wards, epidemiological surveys, isotopic tracer investigations, and extrapolation from animal models. 

Other at-risk groups are hospitalized patients with poor nutrient intakes or those receiving TPN, when fat-soluble vitamin supplements may not fuUy meet requirements. Conversely, ingestion of supraphysiological doses of vitamins A and E has also been reported to induce vitamin K deficiency, probably by competitive mechanisms. Defective blood coagulation and demonstration of abnormal noncar-boxylated prothrombin are at present the only well-established signs of vitamin K deficiency. 

Every human body requires certain amounts of various macro- and micronutrients, water, and fiber to function properly, objective 1 (Section 12.1), Exercise 12.2. The amounts needed vary with a number of factors such as body size, age, and sex. Various countries have established nutritional guidelines in attempts to maintain good health for their citizens. In the United States, the Reference Daily Intake (RDI) and Daily Reference Values (DRV) are designed to represent appropriate nutrient intake for 95% of the population. 

An Estimated Average Requirement (EAR) is the average daily nutrient intake level estimated to meet the requirements of half of the healthy individuals in a group. EARs have not been established for vitamin K, pantothenic acid, biotin, choline, chromium, fluoride, manganese, or other nutrients not yet evaluated via the DRI [cocess... 

Table I presents a general summary of the nature of the criteria of body state used in the establishment of requirements in Recommended Nutrient Intakes for Canadians, The definitions are imprecise, and in the final analysis, the requirement estimates involved a judgement by committee members based on evidence drawn from a number of studies which...

Other approaches have been used to estimate nutrient requirements, such as metabolic balance studies and nutrient analysis of human milk. However, both of these approaches adopt an arbitrary target value to assess response to various nutrient intakes. For the premature infant, whose actual existence outside the womb is unnatural , it is impossible, other than by arbitrary definition, to define and justify goals. Therefore, although the intrauterine accretion data are based on relatively few observations and may be an underestimate of true intrauterine accretion, they presently represent the most appropriate guideline for establishing minimum growth and nutrient accretion goals in the newborn premature infant. 

The Tolerable Upper Intake Limit (UL) for adults is 10 mg daily, based on degree of liver damage associated with intake. UL for children vary with age 1-3 years/1 mg daily, 4—8 years/3 mg daily, 9-13 years/ 5 mg daily, 14—18years/8mg daily (irrespective of pregnancy or lactation status). UL for children imder the age of 1 year are not possible to establish. There are no official recommended daily allowances (RDAs) for copper in children. The RDA for adult males and females is a daily intake of 0.9 mg. Measurements of the dietary requirements for copper in adult men have shovm the requirement to range from about 1.0 to 1.6 mg daily. A review of nutrient intakes in the US from 1909 to 1994 confirms... 

Committees of experts organized by the Food and Nutrition Board of the National Academy of Sciences have compiled Dietary Reference Intakes (DRIs)—estimates of the amounts of nutrients required to prevent deficiencies and maintain optimal health. DRIs replace and expand on Recommended Dietary Allowances (RDAs), which have been published wih periodic revisions since 1941. Unlike the RDAs, the DRIs establish Lpper limits on the consumption of some nutrients, and incorporate the role of nutrients in lifelong health, going beyond deficiency diseases. Boh the DRIs and the RDAs refer to long-term average daily nutrient itakes, because it is not necessary to consume the full RDA every day. 

Chromium(III) is an essential nutrient required for maintaining normal glucose metabolism. The NRC established estimated safe and adequate daily dietary intakes (ESADDIs) of 10-80 pg/day for children aged 1-3 years 30-120 pg/day for children aged 4-6 years, and 50-200 pg/day for children aged 7 years or older (NRC 1989). These recommendations were derived by extrapolating the adult ESADDI value of 50-200 pg/day on the basis of expected food intake. 

Biomarkers of risk, such as DNA adducts, are required that can measure the effects of exposure to a potential carcinogen and the modulating effects of protective factors such as dietary nutrients and phytochemicals. Biomarkers can thus be used to establish the role of phytochemicals in protecting against DNA damage and determine the optimal intake of certain phytochemicals. Application of knowledge of the risk factors involved in cancer formation and also of the role of factors that can protect against cancer in the diet and environment is likely to be instrumental in chemoprevention. 

Requirement is taken to mean that level of dietary intake of a nutrient that meets an individual s need, described as the establishment and maintenance of a reasonable level in tissues or stores in the body. For infants, children and pregnant women, requirement is meant to include needs for the deposition of new tissues, and in lactating women, for the production of milk. As here described, requirements refer to levels of intake needed to maintain health in already healthy individuals. For this purpose, health is considered to be more than the absence of clinically apparent ill health. 

Intravenous requirements for energy, protein, amino acids, vitamins, minerals, and trace metals have not been definitely established for the newborn infant, although significant advances have been made in the past 5 years. Current estimates of intravenous requirements continue to be based on recommended oral intakes and a few nutrient balance studies. In this chapter, it is not possible to provide a detailed review on the termination of intravenous requirements for all the essential nutrients which are recommended for inclusion in TPN regimens. This topic has been the subject of several recent reviews (Jeejeebhoy, 1983 Heim et al, 1981 Zlotkin and Anderson, 1985 Winters et al, 1983). This section will deal with some of the newer issues associated with parenteral nutrition. 

Based on these considerations, the nutrient requirements, including the recommended intake of vitamin A activity for normal growth and development, have been established. Publications are available from the United States National Academy of Sciences for a number of laboratory, domestic, and farm animals and fish. These recommendations are periodically reviewed and updated by expert committees. In addition, the United States National Research Council has published standards for consideration in the control of diets for the conduct of nutrition studies in animals (ILAR Committee on Laboratory Animal Diets, 1977) and the American Institute of Nutrition has published a description of diets suitable for growth, reproduction, and lactation in rats and mice (American Institute of Nutrition, 1977). 

Also on this physiological side there is the fact of adaptation by human beings to intake levels lower than those believed to be required. Whereas adaptation seems to imply an undesirable deprivation, the fact is well established that there is an advantage in eating slightly less than adequate calories, and it may be advantageous under some circumstances to limit the intake of at least certain nutrients (Canadian Council on Nutrition, 1945). 

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