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PART I: APPLYING THE DIETARY REFERENCE INTAKES 19 APPLYING THE DIETARY REFERENCE INTAKES T he goal of dietary assessment is to determine if the nutrient intakes of an individual or group are meeting the needs of that individual or group. The goal of dietary planning is to recommend a diet that provides ad- equate, but not excessive, levels of nutrients. It is important to note that when planning for individuals, the goal is to achieve recommended and adequate nutrient intakes using food-based guides. However, for group planning, this chapter presents a new approach, one based on considering the entire distribu- tion of usual nutrient intakes, rather than focusing on the mean intake of a group. While reading this chapter, keep in mind the following important points: First, the Dietary Reference Intakes (DRIs) apply to healthy people and do not pertain to those who are sick or malnourished or whose special circumstances may alter their nutrient needs. Second, an individualâs exact requirement for a specific nutrient is generally unknown. The DRIs are intended to help practition- ers arrive at a reasonable estimate of the nutrient level required to provide ad- equacy and prevent adverse effects of excess intake. Third, using the DRIs for assessment and planning is most effective when conducted as a cyclical activity that comprises assessment, planning, implementation, and reassessment. When assessing and planning diets, it is important to be mindful of the limitations in the data that underpin the DRIs and their application, which include the following: â¢ The Estimated Average Requirements (EARs) may be based on data from a limited number of individuals. â¢ For most nutrients, the precise variation in requirements is not known but is approximated. â¢ In the absence of evidence to the contrary, variation in individual re- quirements is assumed to follow a normal distribution. â¢ The EAR is often extrapolated from one population group to another. â¢ The degree of uncertainty associated with the EAR has not been specified. The appropriate application of the DRIs represents a significant departure from
DRIs: THE ESSENTIAL GUIDE TO NUTRIENT REQUIREMENTS 20 BOX 1 Definitions Associated with Assessing and Planning Nutrient Intakes Distribution of requirements: The distribution that reflects the individual- to-individual variability in requirements. Variability exists because not all individuals in a group have the same requirements for a nutrient, even if the individuals belong to the same life stage and gender group. Probability of inadequacy: The outcome of a calculation that compares an individualâs usual (long-term) intake to the distribution of requirements for people of the same life stage and gender group; used to determine the probability that the individualâs intake does not meet his or her requirement. Probability of adequacy: 100 percent minus the probability of inadequacy. Prevalence of inadequacy: The percentage of a group with intakes that fall below requirements. how nutrition assessment and planning were carried out using the former Rec- ommended Dietary Allowances (RDAs) and Recommended Nutrient Intakes (RNIs). Although many practitioners may have regarded the use of RDAs and RNIs as a way to determine âexactâ assessments of intake, this presumed level of accuracy was actually misleading. Dietary assessment is not an exact sci- ence. In fact, it generally has always involved a process that included a âbest estimateâ of an individual or groupâs intake. The new DRIs, however, afford an opportunity to substantially improve the accuracy of dietary assessment be- cause they allow practitioners to calculate the probability of inadequacy for an individual and the prevalence of inadequacy within a group and to plan for a low probability of inadequacy while minimizing potential risk of excess (see Box 1). These concepts are explained in greater detail later in this chapter, beginning with a short review of the statistical foundation underlying the con- cept of a distribution.
PART I: APPLYING THE DIETARY REFERENCE INTAKES 21 STATISTICAL FOUNDATION The DRIs and their applications are based on the statistical concept of a distri- bution. A distribution is an arrangement of data values showing their frequency of occurrence throughout the range of the various possible values. One of the most common distributions is a ânormalâ distribution, which is a symmetrical bell-shaped curve that has most of the values clustered in the center of the distribution and a few values falling out in the tails (see Figure 1). Important measures that describe a distribution are the mean, median, and standard deviation. â¢ The mean is the average of the data values. It is calculated by adding all the data values and then dividing by the number of data values. â¢ The median is the data value that occurs right in the middle of the distribution. It is the point at which half the data values are below and half the data values are above. The median is also referred to as the 50th percentile. In a symmetrical/normal distribution, the mean and median occur in the same place. â¢ The standard deviation (SD) is a measure of how much, on average, each individual data value differs from the mean. The smaller the SD, the less each data value varies from the mean. The larger the spread of data values, the larger SD becomes. â¢ The variance is another measure of how much individual data values differ from the mean. It is equivalent to the square of the standard de- viation (SD2). FIGURE 1 Schematic of a normal distribution.
DRIs: THE ESSENTIAL GUIDE TO NUTRIENT REQUIREMENTS 22 EAR 50% 50% 34% 34% RDA 13.5% 13.5% 2.5% 2.5% â3 SD â2 SD â1 SD 0 +1 SD +2 SD +3 SD Mean Median Percentile Rank 2.5 16 50 84 97.5 FIGURE 2 Normal requirement distribution of hypothetical nutrient showing percentile rank and placement of EAR and RDA on the distribution. One important use of the normal distribution is the way it can be used to con- vert scores into percentile ranks, or probabilities. The âz-scoreâ is a standard score that changes values into SD units (i.e., the score is now so many SDs above or below the mean). This score can be related directly to the normal distribution and the associated percentage probability of nutrient adequacy or inadequacy, as seen in Figure 2. By making use of this property of the normal distribution, the probability (or prevalence) of adequacy or inadequacy can be estimated. For example, a z- score of +1.50 is associated with a probability of adequacy of 93 percent. A z-score of â1.00 is associated with a probability of adequacy of 15 percent. Table 1 lists a selection of z-scores and their associated probabilities. It should be noted that not all data will form a normal distribution. For example, a âskewedâ distribution is one where the curve has one tail longer than the other end. If the data do not form a normal distribution, then the properties of the normal distri- bution do not apply.
PART I: APPLYING THE DIETARY REFERENCE INTAKES 23 TABLE 1 Probability of Adequacy for Selected Z- Scores z-score Probability of Adequacy 2.00 0.98 1.65 0.95 1.50 0.93 1.25 0.90 1.00 0.85 0.86 0.80 0.68 0.75 0.50 0.70 0.00 0.50 â0.50 0.30 â0.85 0.20 â1.00 0.15 Applying the DRIs Makes Use of Two Distributions In applying the DRIs, two distributions are used simultaneously. The first is the distribution of requirements. The second is the distribution of intakes. REQUIREMENT DISTRIBUTION The distribution of requirements is the distribution upon which the DRIs (spe- cifically the EAR and RDA) are based. This distribution reflects the variability in requirements between individuals. Variability exists because not all individuals have the same requirement for a nutrient. For nutrients where requirements are normally distributed, the EAR is located at the mean/median of the distribu- tion. The RDA is located at 2 standard deviations above the mean, the level at which 97.5 percent of requirements should be met. INTAKE DISTRIBUTION The distribution of intakes is obtained from observed or reported nutrient in- takes gathered through dietary assessment methods such as 24-hour recalls. A 24-hour recall is a detailed description of all foods and beverages consumed in the previous 24-hour period. Nutrient intake from supplements should also be collected. When more than one 24-hour recall is collected, intake data can reflect the day-to-day variability within an individual that occurs because dif- ferent foods are eaten on different days.
DRIs: THE ESSENTIAL GUIDE TO NUTRIENT REQUIREMENTS 24 When working with individuals, this variability is taken into account in the formulas used for assessment. When working with groups, statistical proce- dures should be used to adjust the distribution of observed intakes by partially removing the day-to-day variability in individual intakes so that the adjusted distribution more closely reflects a usual intake distribution. Usual intake is an important concept in application of the DRIs. Usual intake is the average intake over a long period of time. It is seldom possible to accurately measure long-term usual intake due to day-to-day variation in in- takes as well as measurement errors. Therefore, mean observed intakes (over at least two non-consecutive days or three consecutive days) are used to estimate usual intake. Overlap of the Requirement Distribution and the Intake Distribution The requirement and intake distributions can overlap to varying degrees. In some cases, the two distributions will barely intersect, if at all (see Figure 3, Panel A), and in others there may be a lot of overlap between intakes and re- quirements (see Figure 3, Panel B). In applying the DRIs to assessment, the distribution of intakes is compared to the distribution of requirements and inferences are made about the degree of adequacy. In dietary planning, efforts are made to ensure that the distribution of intakes is adequate relative to the distribution of requirements. WORKING WITH INDIVIDUALS How to Assess the Nutrient Intakes of an Individual The goal of assessing an individualâs nutrient intake is to determine if that in- take is meeting the personâs nutrient requirements. Assessment of dietary ad- equacy for an individual is difficult because of the imprecision involved in esti- mating an individualâs usual intake and the lack of knowledge of an individualâs actual nutrient requirements. Interpreting nutrient intake data in relation to the DRIs can enhance the assessment of an individualâs diet; however, the informa- tion obtained must be interpreted cautiously because an individualâs true usual intake and true requirements must be estimated, and assessment of dietary ad- equacy is only one component of a nutritional status assessment. Ideally, intake data are combined with clinical, biochemical, or anthropometric information to provide a valid assessment of nutritional status. Recognizing the inherent limitations and variability in dietary intakes and requirements is a major step forward in nutrition. The reports on using the DRIs for assessment and planning have provided a method with which one can
PART I: APPLYING THE DIETARY REFERENCE INTAKES 25 Panel A AI Median intake Theoretical requirement distribution Distribution of usual intakes 0 1 2 3 4 5 6 7 Nutrient X (mg/d) AI Median intake Panel B Theoretical Distribution of requirement usual intakes distribution 0 1 2 3 4 5 6 7 Nutrient X (mg/d) FIGURE 3 Overlap of requirement and intake distributions varies. estimate the degree of confidence that an individualâs intake meets his or her requirement. There are also equations that have been developed to estimate the degree of confidence that an individualâs intake is above the AI, and below the Tolerable Upper Intake Level (UL). It is important to keep in mind that the DRIs are estimates based on avail- able data, and that even when an EAR, RDA, and UL for a nutrient are provided for a life stage and gender group, there is considerable uncertainty about these values. Because information on both dietary intakes and requirements are esti- mated, it is very difficult to exactly determine whether an individualâs diet meets his or her individual requirement, even with the statistical approaches described
DRIs: THE ESSENTIAL GUIDE TO NUTRIENT REQUIREMENTS 26 in this chapter. Thus, assessment of dietary intakes should be used as only one part of a nutritional assessment, and the results must be kept in context. Nutri- ent intake data should always be considered in combination with other infor- mation, such as anthropometric measurements, biochemical indices, diagnoses, clinical status, and other factors. Dietary adequacy should be assessed and diet plans formulated based on the totality of evidence, and not on dietary intake data alone. ESTIMATING AN INDIVIDUALâS USUAL INTAKE AND REQUIREMENT To conduct a dietary assessment, information is needed on both dietary intakes and dietary requirements. Information on dietary intake of individuals is usu- ally gathered through food records or dietary recalls, and the requirement esti- mate is provided through the DRI process. In all cases the individualâs usual intake and true requirement can only be approximated. Estimation of Usual Intake Obtaining accurate information on dietary intakes is challenging for a num- ber of reasons, including the accuracy of dietary assessment techniques, as well as the challenges related to variability in intakes. The strongest methods for dietary assessment of nutrient adequacy are 24-hour recalls, diet records, or quantitative diet histories. Even so, the literature indicates that a sizeable pro- portion of individuals systematically misreport their dietary intakes, with the tendency toward underreporting (particularly for energy and percentage of en- ergy from fat). It is unclear how this affects the accuracy of self-reported intakes of nutrients. Well-accepted, validated methods to statistically correct for the effects of underreporting are presently lacking. There is also large day-to-day variation within a given individualâs intake due to factors such as variation in appetite, food choices, day of the week, and season. The result is that the calculation of dietary intake from one or even several days of intake may give an inaccurate estimate of that individualâs usual nutrient intake, especially if food choices vary greatly from one day to the next. Thus, observed dietary intake is probably not the same as the long-term usual intake of an individual. However, the observed mean intake is still the best available estimate of dietary intake, and can still be used providing that it is recognized there is an amount of variability associated with that best estimate. Estimation of Requirement It is nearly impossible to determine what an individualâs exact requirement for a nutrient is, unless that individual has participated in a requirement study.
PART I: APPLYING THE DIETARY REFERENCE INTAKES 27 Therefore, the fall-back assumption is that the individualâs requirement will be close to the average, in which case the EAR is the best estimate for an individualâs unobservable requirement. It is important to note that there is variation in nu- trient requirements between different individuals, and this needs to be taken into account when conducting an assessment. Using a Qualitative Approach to Assess an Individualâs Nutrient Intake Many users of the DRIs may find a qualitative assessment of an individualâs nutrient intakes to be useful. When conducting this type of descriptive assess- ment, it is important to keep in mind the limitations associated with the estima- tion of both intakes and requirements. For nutrients with an EAR and RDA: â¢ Observed mean intake below the EAR very likely needs to be improved (because the probability of adequacy is 50 percent or less). â¢ Observed mean intake between the EAR and the RDA probably needs to be improved (because the probability of adequacy is more than 50 percent but less than 97.5 percent). â¢ Intakes below the RDA cannot be assumed to be inadequate because the RDA by definition exceeds the actual requirements of all but 2â3 per- cent of the population; many with intakes below the RDA may be meet- ing their individual requirements. â¢ The likelihood of nutrient inadequacy increases as usual intake falls further below the RDA. â¢ Only if intakes have been observed for a large number of days and are at or above the RDA should one have a high level of confidence that the intake is adequate. For nutrients with an Adequate Intake (AI): â¢ If observed mean intake equals or exceeds the AI, it can be concluded that the diet is almost certainly adequate. â¢ If, however, observed mean intake falls below the AI, no estimate can be made about the probability of nutrient inadequacy. â¢ Professional judgment, based on additional types of information about the individual, should be exercised when interpreting intakes below the AI.
DRIs: THE ESSENTIAL GUIDE TO NUTRIENT REQUIREMENTS 28 For nutrients with a UL: â¢ Observed mean intake less than the UL is likely to be safe. â¢ Observed mean intake equal to or greater than the UL may indicate a potential risk of adverse effects. The higher the intake in comparison to the UL, the greater the potential risk. For nutrients with an Acceptable Macronutrient Distribution Range (AMDR): â¢ Observed mean intake between the lower and upper bound of the AMDR is within the acceptable range. â¢ Observed mean intake below the lower bound or above the upper bound of the AMDR may heighten concern for possible adverse consequences. For energy: â¢ Body mass index (BMI) should be used to assess the adequacy of energy intake, rather than a comparison to the Estimated Energy Requirement (EER). Using a Quantitative Approach to Assess an Individualâs Nutrient Intake An approach has been developed that statistically estimates the level of confi- dence that an individualâs usual intake is above an individualâs requirement, or below the UL. The equations developed for the assessment of individuals are based on the principles of hypothesis testing and levels of confidence based on a normal distribution curve. The equations proposed here are not applicable to all nutrients because they assume a normal distribution of daily intakes and requirements. For nutri- ents for which a distribution is skewed (such as iron requirements of menstru- ating women, or dietary intakes of vitamin A, vitamin B12, vitamin C, and vita- min E), a different methodology needs to be developed. For these nutrients, individual assessment should continue to place emphasis on other types of information available. NUTRIENTS WITH AN EAR For nutrients with an EAR, a z-score is calculated using the following equation: mean observed intake â EAR z - score = [(SD of requirement) +(within - person SD)2 / number of days of intake records] 2
PART I: APPLYING THE DIETARY REFERENCE INTAKES 29 The use of this equation requires the following information: â¢ Mean observed intake: The mean nutrient intake of an individual is the best estimate of an individualâs usual intake. â¢ EAR: The EAR is the best estimate of an individualâs requirement for a nutrient. â¢ SD (standard deviation) of requirement: This is the variation in require- ments between individuals. It is calculated as the coefficient of variation (CV) times the EAR (see Appendix H). â¢ Within-person SD of intake: The variation in day-to-day nutrient intake within the individual is an indicator of how much observed intake may deviate from usual intake. (This has been estimated in the original DRI reports by using CSFII data; see Appendix I.) â¢ The number of days of intake records or recalls. As illustrated in Box 2, the equation solves for a z-score on the normal distribu- tion curve. Some z-scores and their associated probabilities are listed in Table 1. The larger the z-score, the larger the probability associated with that value. The numerator of the equation is the difference between the estimated intake and the estimated requirement. It can intuitively be seen that the higher an intake is compared to the requirement, the larger the numerator will be. The denomina- tor of the equation is the term that incorporates all the variability. Thus, as the variability gets smaller, the z-score will get larger. Note that an increase in the number of days of records will lead to a decrease in the amount of variability. NUTRIENTS WITH AN AI For nutrients with an AI it is not possible to estimate the requirement of indi- viduals. The AI represents an intake (not a requirement) that is likely to exceed the actual requirements of almost all individuals in a life stage and gender group. In fact, the AI may even be higher than an RDA (if it was possible to calculate one). When trying to compare an individualâs intake to his or her requirement, the AI is not very useful because it is in excess of the median requirement, perhaps by a very large margin. Therefore, when intakes are compared to the AI, all that can be concluded is whether the intake is above the AI or not. It is possible to determine the confidence with which one can conclude that usual intake exceeds the AI using the following equation:
DRIs: THE ESSENTIAL GUIDE TO NUTRIENT REQUIREMENTS 30 BOX 2 Example: Using the Quantitative Approach for Individual Assessment for a Nutrient with an EAR Suppose a 40-year-old woman had a magnesium intake of 320 mg/day, based on 3 days of dietary records. The question is whether this observed mean intake of 320 mg/ day indicates that her usual magnesium intake is adequate. To determine the probability that her usual intake meets her requirement, the following data are used: â¢ The mean observed intake for this woman is 320 mg/day. â¢ The EAR for magnesium for women 31â50 years is 265 mg/day â¢ The SD of the requirement distribution for magnesium is 10 percent of the EAR (Appendix H), therefore 26.5 mg/day. â¢ The within-person SD (day-to-day variability) in magnesium intake for women this age is estimated to be 86 mg/day (Appendix I). â¢ There are 3 days of dietary records. Solving for the z-score yields: 320 â 265 55 = = 0.98 Âª 1.0 z - score = 56 2 2 [(26.5) + (86) / 3] Table 1 lists a selection of and their associated probabilities. Looking up a z-score of 1.0, it can be seen that 85% probability of correctly concluding that this intake is ad- equate for a woman in this age category. mean observed intake â AI z - score = within - person SD / number of days of intake records The use of this equation requires the following information: â¢ Mean Observed Intake: The individualâs mean observed intake â¢ AI: The AI for a similar life stage and gender group
PART I: APPLYING THE DIETARY REFERENCE INTAKES 31 â¢ Within-person SD of intake: The variation in day-to-day nutrient intake within the individual is an indicator of how much observed intake may deviate from usual intake (see Appendix I) â¢ The number of days of intake records or recalls Solving for the equation gives the confidence with which one can conclude that usual intake is greater than the AI. If an individualâs intake equals or ex- ceeds the AI, it can be concluded that the diet is almost certainly adequate. However, if the calculation does not result in the conclusion that there is a high probability that the usual intake is larger than the AI, it cannot be inferred that intake is inadequate. Professional judgment, based on additional types of information about the individual, should be exercised when interpreting in- takes below the AI. NUTRIENTS WITH A UL The UL can be used to assess the likelihood that an individual may be at risk of adverse effects from high intakes of that nutrient. An equation has been deter- mined to assess the probability that usual intake is below the UL given the mean observed intake. This equation is useful because even when mean ob- served intake is less than the UL, it cannot always be concluded with the de- sired amount of accuracy that usual intake is also below the UL (due to the variability associated with observed intake). This is particularly the case when the observed mean intake is a value close to that of the UL (as could be the case when considering intake from food plus supplements). When using a UL to assess a personâs nutrient intake, it is important to know whether the UL applies to intake from all sources or just from specific sources, such as supplements, fortified foods, or pharmacological preparations. The equation is as follows: mean observed intake â UL z - score = within - person SD / number of days of intake records The use of this equation requires the following information: â¢ Mean Observed Intake: The individualâs mean observed intake (from applicable sources) â¢ UL: The UL for a similar life stage and gender group â¢ The within-person SD of intake: The variation in day-to-day nutrient intake within the individual is an indicator of how much observed in- take may deviate from usual intake (see Appendix I) â¢ The number of days of intake records or recalls
DRIs: THE ESSENTIAL GUIDE TO NUTRIENT REQUIREMENTS 32 Solving for the equation yields the confidence with which one can conclude that usual intake is less than the UL. Intakes less than the UL are likely to be safe; and intakes equal to or greater than the UL may indicate a potential risk of adverse effects. The higher the intake in comparison to the UL, the greater the potential risk. The consequences associated with nutrient excess vary for different nutri- ents. It should also be noted that the UL does not apply to individuals who are consuming high intakes of nutrient on the advice of a physician who is moni- toring the nutritional status of the individual. NUTRIENTS WITH AN AMDR The AMDRs represent intakes of macronutrients that minimize the potential for chronic disease over the long term, permit essential nutrients to be consumed at adequate levels, and are associated with adequate energy intake and physical activity to maintain energy balance. To estimate the degree of confidence that an individualâs diet falls within the AMDR, the equations developed for the AI and the UL can be used. The equation for the AI can be used to determine the degree of confidence that intake is above the lower bound of the AMDR, and the equation for the UL can be used to determine the degree of confidence that intake is below the upper bound of the AMDR. Practically, observed mean intake between the lower and upper bounds of the AMDR is within the acceptable range. Observed mean intake below the lower bound or above the upper bound of the AMDR may heighten concern for possible adverse consequences. ENERGY Theoretically, the usual energy intake of an individual could be compared with his or her requirement to maintain current weight with a certain level of physi- cal activity, as estimated using the EER equations. However, by definition, the EER provides an estimate that is the midpoint of the range within which the energy expenditure of an individual could vary, and the individualâs actual ex- penditure could be considerably above or below this estimated midpoint. Ac- cordingly, comparing an individualâs intake with the calculated average expen- diture is essentially meaningless because of the difficulty in interpreting the result. In contrast, BMI provides a useful indicator of the adequacy of usual en- ergy intake in relation to usual energy expenditure. A BMI within the normal range of 18.5 up to 25 kg/m2 (for adults) indicates that energy intake is ad- equate relative to expenditure. A BMI below the normal range indicates inad- equate energy intake, whereas a BMI above the normal range is indicative of excessive energy intake.
PART I: APPLYING THE DIETARY REFERENCE INTAKES 33 Quantitative vs. Qualitative Approaches to Dietary Assessment of Individuals Box 2 provides a brief example of a quantitative assessment for a nutrient (mag- nesium) with an EAR. A qualitative assessment could be done using the same mean intake of 320 mg/day. This value is higher than the EAR (265 mg/day) and equal to the RDA (320 mg/day). Thus, it would be assumed that the womanâs intake was almost certainly adequate, when in fact there is only 85 percent confidence that this intake is adequate. The shortcoming of the qualitative method is that it does not incorporate any variability at all. If the variability in magnesium intake was even larger than 86 mg/day, the probability that an intake of 320 mg is adequate for this woman would be even lower than 85 percent, but the result of the qualitative assess- ment would not change at all. For this reason it is strongly encouraged that the statistical method be the method of choice when assessing nutrient adequacy, because even an intake that looks as though it is at the upper end of the distribution (e.g., at or above the RDA) may have an unacceptably low probability of being adequate depend- ing on the amount of variability associated with the estimated intake. Using the DRIs to Plan an Individualâs Diet The goal for individual planning is to ensure that the diet, as eaten, has an acceptably low risk of nutrient inadequacy while simultaneously minimizing the risk of nutrient excess. More simply put, the goal is to plan an individualâs intake that will result in a low risk of that person not meeting his or her requirements. For nutrients that have an RDA, this value should be used as a guide for planning. For nutrients with an AI, the AI should be used. The EAR should not be used for planning an individualâs nutrient intake because, by definition, a diet that provides the EAR of a nutrient has a 50 percent likelihood of not meeting an individualâs requirement. Planning diets for individuals involves two steps: First, appropriate nutri- ent intake goals must be set, taking into account the various factors that may affect a personâs nutrient needs. For example, a person who smokes may have greater needs for vitamin C. Second, the diet developed should be one that the individual can afford and will want to consume. Food-based education tools such as the United States Department of Agricultureâs (USDAâs) Food Guide Pyramid and Canadaâs Food Guide are commonly used by practitioners to teach individuals how to plan healthful diets that are adequate in nutrients. Dietary planning involves using the DRIs to set goals for what intakes should be. When planning for nutrients such as vitamins, minerals, and protein, a low
DRIs: THE ESSENTIAL GUIDE TO NUTRIENT REQUIREMENTS 34 Individual Are there "special considerations"? No Yes e.g., smoker (vitamin C) athlete (iron) Plan so that the RDA or AI for vegetarian (iron, zinc) age/sex is met Remain below the UL ill person (nutrients affected by illness) Other nutrients Plan for appropriate intakes of specific nutrients of concern based on special considerations FIGURE 4 Decision tree for planning diets of individuals. risk of inadequacy is planned for by meeting the RDA or AI, and a low risk of excess is planned by remaining below the UL. In some cases it may be appropriate to use a target other than the RDA for individuals since the DRIs apply only to the apparently healthy population. Special guidance should be provided for those with greatly increased or de- creased needs. Although the RDA or AI may serve as the basis for such guid- ance, qualified health care personnel should make the necessary adaptations for specific situations. Figure 4 is a flow chart that describes decisions that need to be made during the planning process. PLANNING NUTRIENT INTAKES FOR AN INDIVIDUAL USING THE RDA The RDA may be used for planning nutrient intakes that result in an acceptably low probability of inadequacy for an individual. The RDA is intended to en- compass the normal biological variation in the nutrient requirements of indi- viduals. It is set at a level that meets or exceeds the actual nutrient requirements of 97â98 percent of individuals in a given life stage and gender group. This level of intake, at which there is a 2â3 percent probability of an individual not meeting his or her requirement, has traditionally been adopted as the appropri- ate reference for planning intakes for individuals. There are neither adverse effects nor documented benefits associated with exceeding the RDA, provided that intake remains below the UL. When coun-
PART I: APPLYING THE DIETARY REFERENCE INTAKES 35 seling an individual, a practitioner must consider whether there is any recog- nizable benefit to increasing an individualâs current intake level. The likelihood of the benefit must be weighed against the cost, monetary and otherwise, likely to be incurred by increasing the intake level. If intake levels other than the RDA are chosen, they should be explicitly justified. For example, for women between the ages of 19 and 30 years, the RDA for iron is 18 mg/day, which was set to cover the needs of women with the highest menstrual blood losses. A particular woman might feel that her men- strual losses are light and, accordingly, she may be willing to accept a 10 per- cent risk of not meeting her requirement and thus would have an intake goal of only 13 mg/day (see Part III, âIronâ; Part IV, âAppendix Gâ). The EAR is not recommended for planning nutrient intakes of individuals. Despite the fact that the EAR is the best estimate of an individualâs requirement, by definition, half the individuals in a group have requirements that are higher than the EAR. Accordingly, an intake at the level of the EAR is associated with a probability of inadequacy of 50 percent and is not suitable as a goal for plan- ning. As intake increases above the EAR, the probability of inadequacy decreases and reaches 2â3 percent with intakes at the RDA. PLANNING NUTRIENT INTAKES FOR AN INDIVIDUAL USING THE AI When scientific evidence is not sufficient to set an EAR and thus calculate an RDA for a particular nutrient, an AI is usually developed. Under these circum- stances, the AI is the recommended target for planning the nutrient intakes of individuals. Although greater uncertainty exists in determining the probability of inadequacy for a nutrient that has an AI instead of an RDA, the AI provides a useful basis for planning. Intake at the level of the AI is likely to meet or exceed an individualâs requirement, although the possibility still exists that it could fail to meet the requirements of some individuals. The probability of inadequacy associated with a failure to achieve the AI is unknown. PLANNING NUTRIENT INTAKES FOR AN INDIVIDUAL USING THE UL The UL can be used to plan intakes that have a low probability of adverse effects resulting from excessive consumption. The UL is not a recommended level of intake, but rather an amount that can be biologically tolerated with no apparent risk of adverse effects by almost all healthy people. Thus, the goal for planning an individualâs diet is to not exceed the UL. It is important to note that for many nutrients the UL applies to intake from all sources, whereas for some it may only apply to intake from certain sources, such as supplements, fortificants, and pharmacological preparations. (The profiles of individual nutrients found in Part III provide this information.)
DRIs: THE ESSENTIAL GUIDE TO NUTRIENT REQUIREMENTS 36 For most nutrients, intakes at or above the UL would rarely be attained from unfortified food alone. PLANNING NUTRIENT INTAKES FOR AN INDIVIDUAL USING THE AMDR In addition to meeting the RDA or AI, and remaining below the UL, an individualâs intake of macronutrients should be planned so that carbohydrate, fat, and pro- tein are within their respective acceptable ranges. PLANNING ENERGY INTAKES FOR AN INDIVIDUAL The underlying objective of planning for energy is similar to planning for other nutrients: to attain an acceptably low risk of inadequacy and of excess. How- ever, the approach to planning for energy differs substantially from planning for other nutrients. When planning for individuals for nutrients such as vitamins and minerals, there are no adverse effects to consuming an intake above an individual requirement, provided intake remains below the UL. The situation for energy is quite different because for individuals who consume energy above their requirements and needs over long periods of time, weight gain will occur. This difference is reflected in the fact that there is no RDA for energy, as it would be inappropriate to recommend an intake that exceeded the requirement for a large number of individuals. Thus, the requirement for energy is expressed as an EER. As explained in Part II, an EER is based on energy expenditure and is de- fined as the average dietary energy intake required to maintain current body weight and activity level (and to allow for growth or milk production, as appro- priate) in healthy, normal-weight individuals of specified age, sex, height, weight, and physical activity level (PAL) that is consistent with good health. The best way to plan for energy intake of individuals is to consider their body weight or BMI. When body weight is stable in normal-weight individuals (BMI of 18.5 kg/m2 up to 25 kg/m2), the energy requirement is equal to total energy expenditure and is also the usual intake. The prediction equations to calculate an EER can be used as a starting point for planning (see Part II, âEnergyâ). They are only a starting point because energy expenditures vary from one individual to another even though their characteristics may be similar. The EER is the midpoint of a range of energy requirements. By definition, the EER would be expected to underestimate the true energy expenditure 50 percent of the time and to overestimate it 50 per- cent of the time. These errors in estimation would eventually lead to a gain or loss in body weight, which would be undesirable when the goal is to maintain a healthy weight. Body weight should be monitored and the amount of energy in the diet adjusted up or down from the EER as required to maintain an appro-
PART I: APPLYING THE DIETARY REFERENCE INTAKES 37 priate body weight. Additionally, self-reported energy intake should not be re- lied on to determine a personâs energy needs, since underreporting of intakes is a serious and pervasive problem. Developing Dietary Plans for an Individual Once appropriate nutrient intake goals have been identified for the individual, these must be translated into a dietary plan that is acceptable to the individual. This is most frequently accomplished using nutrient-based food guidance systems such as national food guides. Special Considerations Factors such as nutrient bioavailability and physiological, lifestyle, and health characteristics may alter nutrient requirements and lead to the need for adjust- ments in DRI values when planning dietary intakes. Table 2 summarizes some common special considerations.
DRIs: THE ESSENTIAL GUIDE TO NUTRIENT REQUIREMENTS 38 TABLE 2 Common Reasons for Adjustment in DRI Values When Planning Dietary Intake Consideration Nutrient Adjustment Recommended Folic acid for women of It is recommended that all women consumption from childbearing age capable of becoming pregnant take 400 mg folic acid every day from fortified synthetic sources foods, supplements, or both, in addition to the amount of food folate found in a healthful diet. Vitamin B12 for those It is advisable for those older than 50 older than 50 years of years to meet the RDA mainly by age consuming foods fortified with vitamin B12 or a supplement containing vitamin B12. Smoking Vitamin C The requirement for smokers is increased by 35 mg/day. Bioavailability in Iron The requirement for iron is 1.8 times vegetarian diets higher for vegetarians due to the lower bioavailability of iron from a vegetarian diet. Zinc The requirement for zinc may be as much as 50 percent greater for vegetarians, particularly for strict vegetarians whose major food staples are grains and legumes. Age of menstruation Iron (it is assumed that If menstruation occurs prior to age 14, an girls younger than 14 additional amount (about 2.5 mg/day) years do not menstruate would be needed to cover menstrual and that girls 14 years blood losses. Conversely, girls ages 14 and older do menstruate) and above who are not yet menstruating can subtract 2.5 mg from the RDA for this age group. Athletes engaged in Iron Average requirements for iron may range regular intense exercise from 30 to 70 percent above those for normally active individuals. Recommendation set Protein Recommendation is set in g/kg/day. RDA according to reference for adults is 0.80 g/kg/day. weight Recommendation set Fiber Recommendation is 14 g/1,000 kcal. per 1,000 kcal
PART I: APPLYING THE DIETARY REFERENCE INTAKES 39 KEY POINTS FOR WORKING WITH INDIVIDUALS ASSESSING NUTRIENT INTAKES The goal of assessing an individualâs nutrient intake is to 3 determine if that intake is meeting his or her nutrient requirements. Assessment requires using the individualâs observed or 3 reported mean intake as an estimate of usual intake and using the EAR of the appropriate life stage and gender group as an estimate of the individualâs requirement. For nutrients with an EAR, a statistical equation can be applied 3 to assess the likelihood of adequacy. This equation yields a z- score that allows a practitioner to determine a probability value that reflects the degree of confidence that the personâs usual intake meets his or her requirement. For nutrients with an AI, a statistical equation can be applied to 3 determine whether usual intake is at or above the AI, in which case intake is deemed adequate. Intakes below the AI cannot be assessed. For nutrients with a UL, a statistical equation can be applied to 3 determine whether usual intake falls below the UL, in which case the person is assessed as having a low risk of adverse effects related to excessive intake. The RDA should not be used for assessing an individualâs 3 intake. In all cases, individual assessments should be cautiously 3 interpreted, preferably in combination with other information on factors that can affect nutritional status, such as anthropometric data, biochemical measurements, dietary patterns, lifestyle habits, and the presence of disease. PLANNING NUTRIENT INTAKES The goal of planning nutrient intakes for individuals is to 3 achieve a low probability of inadequacy while not exceeding the UL for each nutrient. Planning diets for individuals involves two steps: First, 3 appropriate nutrient goals must be set, taking into account the various factors that may affect a personâs nutrient needs. Second, the diet developed should be one that the individual can afford and will want to consume.
DRIs: THE ESSENTIAL GUIDE TO NUTRIENT REQUIREMENTS 40 For nutrients with an EAR and an RDA, the probability of 3 inadequacy is 50 percent at the EAR and 2â3 percent at the RDA. Thus, the RDA is often used as a guide for planning for individuals. If an RDA, is not available, the AI should be used as a guide for planning nutrient intake. For nutrients with a UL, this value should be used as the level 3 not to exceed. An individualâs intake of macronutrients should be planned so 3 that carbohydrate, fat, and protein are within their respective AMDRs. The best way to plan for energy intake of individuals is to 3 consider the healthfulness of their body weight or BMI. WORKING WITH GROUPS Although some nutrition professionals primarily work with individuals, others need to be able to assess and plan the nutrient intakes of groups. Examples of such groups include nursing home residents, research study participants, and children attending residential schools. This section describes ways to assess and plan nutrient intakes of groups. How to Assess the Nutrient Intakes of a Group The goal of assessing the nutrient intakes of groups is to determine the preva- lence of inadequate (or excessive) nutrient intakes within a particular group of individuals (see Box 1 for definitions). Within any given group, even a homoge- neous group such as individuals in the same life stage and gender group, vari- ability will exist among the different individualsâ nutrient needs and nutrient intakes. To accurately determine the proportion of a group that has a usual intake of a nutrient that is less than their requirement, information on both the distribution of usual intakes and the distribution of requirements in the group is needed. Several characteristics of dietary intake data make estimating the distribu- tion of usual intakes for a group challenging. When single 24-hour recalls or diet records are obtained from members of a group, the variability of the nutri- ent intakes will reflect both differences between individuals as well as differ- ences within individuals (i.e., on any given day, a particular individual could eat much more or much less of a nutrient than usual). To obtain a distribution of usual intakes for a group, the distribution of observed intakes (i.e., the intake obtained from a single 24-hour recall) must
PART I: APPLYING THE DIETARY REFERENCE INTAKES 41 Percentage of Individuals Adjusted (usual intake) distribution Unadjusted (1-day intake) distribution Nutrient Intake (unit/d) FIGURE 5 Comparison of 1-day and usual intakes. be statistically adjusted to remove the effects of within-person variability, so that the distribution reflects only between-person variability. To do this, at least two 24-hour recalls or diet records obtained on nonconsecutive days (or at least three days of data from consecutive days) are needed from a represen- tative subsample of the group. When this adjustment is performed, the intake distribution narrows (i.e., the tails of the distribution draw closer to the cen- ter). If intake distributions are not properly adjusted, the prevalence of nutri- ent inadequacy will be incorrectly estimated and is usually overestimated (see Figure 5). Several methods to obtain usual intake distributions are available. The National Research Council (NRC) and Iowa State University have both devel- oped software programs for adjusting intake distributions. Further information is available at http://cssm.iastate.edu/software/side.html. Although these meth- ods will adjust for variability in day-to-day intakes, they do not make up for inaccuracies in reported or observed intakes. The summary below explains how the DRIs are appropriately used in the assessment of a groupâs nutrient intakes. Further explanation of the approach and the methods used are provided in the sections that follow:
DRIs: THE ESSENTIAL GUIDE TO NUTRIENT REQUIREMENTS 42 â¢ For nutrients with an EAR, the EAR can be used to estimate the preva- lence of inadequate intakes using the probability approach or a shortcut derived from the probability approach called the EAR cut-point method. â¢ The RDA is inappropriate for assessing nutrient intakes of groups be- cause the RDA is the intake level that exceeds the requirements of a large proportion of individuals in a group. Consequently, estimating the prevalence of nutrient inadequacy in a group by determining the pro- portion of individuals with intakes below the RDA leads to an overesti- mation of the true prevalence of inadequacy. â¢ For nutrients without an EAR, the AI is instead used. Groups with mean or median intakes at or above the AI can generally be assumed to have a low prevalence of inadequate intakes. â¢ For nutrients with a UL, this value can be used to estimate the propor- tion of a group at potential risk of adverse effects from excessive nutri- ent intake. â¢ For nutrients with an AMDR, the proportion of the group that falls be- low, within, and above the AMDR can be used to assess population adherence to the recommendations and to determine the proportion of the population that is outside the range. If significant proportions of the population fall outside the range, concern could be heightened for pos- sible adverse consequences. â¢ For energy, the distribution of BMI within a group can be assessed, and the proportions of the group with BMIs below, within, and above the desirable range would reflect the proportions with inadequate, adequate, and excessive energy intakes. USING THE PROBABILITY APPROACH TO ASSESS PREVALENCE OF NUTRIENT INADEQUACY IN A GROUP The probability approach is a statistical method that involves determining the probability of inadequacy of the usual intake level for each person in the group and then averaging these individual probabilities across the group to obtain an estimate of the groupâs prevalence of inadequacy. This method depends on two key assumptions: that intakes and requirements are independent and thus no correlation exists between usual intakes and requirements (this is thought to be true for most nutrients, although it is not known to be true for energy) and that the distribution of requirements for the nutrient in question is known. This method then uses statistical equations to estimate the prevalence of inadequacy. Case studies one and two at the end of the chapter illustrate the use of the probability approach. Practically, this approach will most likely be used only when the EAR cut-point method cannot be used.
PART I: APPLYING THE DIETARY REFERENCE INTAKES 43 USING THE EAR CUT-POINT METHOD TO ASSESS PREVALENCE OF NUTRIENT INADEQUACY IN A GROUP The EAR cut-point method is a shortcut derived from the probability approach. When certain conditions are satisfied, the proportion of the group with intakes below the EAR will be similar to the proportion that does not meet their re- quirement. The conditions (assumptions) that must be satisfied to use the EAR cut-point method are: â¢ Intakes and requirements must not be correlated: This is thought to be true for most nutrients, but is known not to be true for energy, as individuals with higher energy requirements have higher energy intakes. â¢ The distribution of requirements must be symmetrical: This is thought to be true for most nutrients, but is known not to be true for iron for men- struating women. Blood (and therefore iron) losses during menstrual flow greatly vary among women, and some women have unusually high losses. As a result, the distribution of iron requirements for this life stage and gender group is skewed rather than symmetrical, and the EAR cut- point method cannot be used to assess the prevalence of inadequacy. Instead, the probability approach should be used, as shown in case study two. â¢ The distribution of intakes must be more variable than the distribution of requirements: Stated another way, the SD of the intake distribution is greater than the SD of the requirement distribution. This is thought to be true among groups of free-living individuals. Note, however, that the assumption that intakes are more variable than requirements might not hold for groups of similar individuals who were fed similar diets (e.g., prison inmates). If the assumption is not met, the probability method can be used instead of the EAR cut-point method. The reasons that the EAR cut-point method can approximate the prevalence of inadequacy in a group as determined by the full probability method are ex- plained below and illustrated in the third case study at the end of the chapter. 1. Although the probability of inadequacy exceeds 50 percent when usual intakes are below the EAR, not everyone with an intake below the EAR fails to meet his or her own requirement: Some individuals with lower-than-average requirements will have adequate intakes (their usual intake, although below the EAR, exceeds their own requirement). 2. Similarly, although the probability of inadequacy is less than 50 percent when usual intakes are above the EAR, not everyone with intakes above the EAR meets their own requirement. Some individuals with higher-than-average
DRIs: THE ESSENTIAL GUIDE TO NUTRIENT REQUIREMENTS 44 requirements will have inadequate intakes (their usual intake, although above the EAR, is below their own requirement). 3. When the requirement distribution is symmetrical, when intakes are more variable than requirements, and when intakes and requirements are inde- pendent, the proportion of the group described in item 1 cancels out the pro- portion described in item 2. The prevalence of inadequacy in the group can thus be approximated by the proportion with usual intakes below the EAR. See Box 3 for an example. THE RDA IS INAPPROPROPRIATE FOR ASSESSING GROUP NUTRIENT INTAKES It is not appropriate to use the RDA to assess nutrient intakes of groups. In the past, the RDA, or the RNI in Canada, has been used incorrectly to make infer- ences about nutrient inadequacy in groups by using the RDA as a cut-point or comparing mean or median intakes with the RDA. The RDA should not be used as a cut-point because it overestimates the requirements of 97.5 percent of the population. The mean or median intake of a group should not be compared with the RDA to assess nutrient adequacy in a group because the prevalence of inadequacy depends on the distribution of usual intakes, and this is not taken into account when only the mean or median is used. For example, as shown in Box 3, women 51 to 70 years of age had a median dietary vitamin B6 intake of 1.51 mg/day in the Third National Health and Nutrition Examination Survey (NHANES III, 1988â1994). Comparing this median intake with the RDA for this group, 1.5 mg/day, might lead one to believe that inadequate vitamin B6 intake is not a problem. However, appropri- ate analysis of the data relative to the EAR reveals that the prevalence of inad- equacy in this group is actually greater than 25 percent. USING THE AI TO ASSESS A GROUPâS NUTRIENT INTAKES The AI has limited uses in assessing the nutrient intakes of groups. When an AI is set for a nutrient, it means that there was insufficient evidence to establish the distribution of requirements and thereby determine an EAR. For this reason, it is simply not possible to determine the proportion of a group with intakes below requirements. Accordingly, only limited inferences can be made about the adequacy of group intakes. If the median or mean intake of a group is at or above the AI, it can be assumed that the prevalence of inadequate intakes in the group is low. If group median or mean intake is below the AI, nothing can be concluded about the prevalence of inadequacy. Again, this occurs because we do not know the requirement distribution, and whether its upper end (if it could be deter-
PART I: APPLYING THE DIETARY REFERENCE INTAKES 45 BOX 3 Assessing Group Nutrient IntakesâThe RDA Is Inappropriate The EAR for vitamin B6 for women aged 51â70 years is 1.3 mg /day and the RDA is 1.5 mg/day. Shown below is a distribution of dietary vitamin B6 intakes for a group of women 51â70 years of age. The distribution has been adjusted for individual variability using the method developed by the National Research Council. The data are from NHANES III. Selected Percentiles of Dietary Vitamin B6 Intake, Women 51-70 Years of Age, NHANES III Percentile 5th 10th 15th 25th 50th 75th 85th 90th 95th Vitamin B6 intake (mg/day) 0.92 1.02 1.11 1.24 1.51 1.90 2.13 2.31 2.65 Comparing the median intake of 1.51 mg/day to the RDA of 1.5 mg/day for this group might lead one to believe that inadequate vitamin B6 intake is not a problem. However, comparison of the distribution of usual intakes to the EAR cut-point shows that the EAR value of 1.3 mg/day falls somewhere between the 25th percentile and the 50th percentile of usual intakes. Thus, it can be concluded that greater than 25 percent of usual intakes are below the EAR cut-point and the prevalence of inadequacy in this group is estimated to be greater than 25 percent (but less than 50 percent). mined) is relatively close to the AI or falls well below it. It follows from the above discussion that individuals with intakes below the AI cannot be assessed as having inadequate intakes. Although the proportion of a group with usual intakes below the AI could be determined, great care should be taken to avoid implying that this proportion does not meet their requirements (i.e., the AI should not be used as a cut-point in the way that the EAR may be). USING THE UL TO ASSESS A GROUPâS NUTRIENT INTAKES The UL can be used to estimate the proportion of a group with intakes above the UL and, therefore, at potential risk of adverse health effects from excess nutrient intake. The method for applying the UL is similar to the EAR cut-
DRIs: THE ESSENTIAL GUIDE TO NUTRIENT REQUIREMENTS 46 point method in that the proportion of the group with intakes above the UL is determined. Because ULs for nutrients are based on different sources of intake, the ap- propriate usual intake distribution must be used in the assessment. For some nutrients, such as fluoride, phosphorus, and vitamin C, the distribution of usual intakes would need to include intake from all sources. For others, such as mag- nesium, folate, niacin, and vitamin E, only the distribution of usual intakes from synthetic sources added to foods and from supplements (and in the case of magnesium, medications) would be needed. Another issue to consider when interpreting the proportion of a group with intakes above the UL is that there is considerable uncertainty with regard to some of the ULs for children. In many cases, these ULs were established based on extrapolation from the ULs for adults or infants, and thus for some nutrients, this resulted in very small margins or an overlap between the adult RDA and the UL for young children. Surveys in the United States have revealed that young children have a high prevalence of intakes above the UL for nutri- ents such as vitamin A and zinc; however, few studies have been conducted in children to assess the effects of such intakes. USING THE AMDR TO ASSESS A GROUPâS NUTRIENT INTAKE By determining the proportion of the group that falls below, within, and above the AMDR, it is possible to assess population adherence to the recommenda- tions and to determine the proportion of the population that is outside the range. If significant proportions of the population fall outside the range, con- cern could be heightened for possible adverse consequences. ASSESSING THE ENERGY ADEQUACY OF A GROUPâS DIET The probability approach and the EAR cut-point method do not work for as- sessing energy adequacy. This is because empirical evidence indicates a strong correlation between energy intake and energy requirement. This correlation most likely reflects either the regulation of energy intake to meet needs or the adjustment of energy expenditure to be consistent with intakes. Therefore, the use of BMI as a biological indicator is preferable. The distribution of BMI within a population group can be assessed, and the proportions of the group with BMIs below, within, and above the desirable range would reflect the propor- tions with inadequate, adequate, and excessive energy intakes. How to Plan for the Nutrient Intakes of a Group The goal of planning nutrient intakes for groups is to achieve usual intakes in the group that meet the requirements of most individuals, but that are not
PART I: APPLYING THE DIETARY REFERENCE INTAKES 47 excessive. This can be challenging because the amount and selection of foods that group individuals eat will vary, even if the same meal is offered. Situations where group planning occurs include residential schools, prisons, military gar- risons, hospitals, nursing homes, child nutrition programs, and food assistance programs. When planning for groups, a practitioner should aim for a low prevalence of inadequate intakes. In the past, this may have involved considering the aver- age intake of the group and comparing it with the RDA, which was inappropri- ate because even if a groupâs average intake meets the RDA, the prevalence of inadequacy is likely to be unacceptably high. This is because the variability in nutrient intakes among group members usually exceeds the variability in the requirements of group members, and it is the variability in requirements that is used to set the RDA. Instead, the new DRIs present an approach to planning that involves con- sideration of the entire distribution of usual nutrient intakes within a group, rather than just the average intake of the group. The goal is that the distribution of usual nutrient intakes that results from the plan will have a low prevalence of inadequate or excessive intake, as defined by the proportion of individuals in the group with usual intakes less than the EAR or greater than the UL. An important caveat: By focusing explicitly on the distribution of nutrient intakes of a group as the goal of group planning, the framework presented here is, in many respects, a new paradigm, and it should be tested before being imple- mented in large-scale group-feeding situations. To apply the framework presented here, an acceptable prevalence of inad- equacy must be defined (a critical step on the part of the planner) and the distribution of usual intakes in the group must be estimated. As previously stated, this is accomplished by determining the distribution of reported or ob- served intakes, and performing a statistical adjustment to estimate the distribu- tion of usual intakes. A target (desired) usual intake distribution can then be determined by positioning the distribution of usual intakes relative to the EAR to achieve the desired prevalence of inadequacy. Because the goal of planning is to achieve a target distribution of usual intakes, assessment must occur (see âProbability Approachâ and âEAR Cut-Point Methodâ earlier in the chapter). In most cases, planning group intakes is an ongoing process, in which planners set goals for usual intake, implement the plan, assess whether the goals have been achieved, and then accordingly modify their planning procedures. Before describing how the different DRI values are appropriately used to plan intakes for groups, the next section explains the importance of a target usual intake distribution and how to estimate this distribution for nutrients with normal distributions and for nutrients with skewed distributions.
DRIs: THE ESSENTIAL GUIDE TO NUTRIENT REQUIREMENTS 48 What Is a Target Usual Nutrient Intake Distribution? Suppose a practitioner is interested in planning a group diet with a high prob- ability of nutrient adequacy (e.g., such that the prevalence of inadequacy in the group is no more than 2â3 percent). Given this target, and assuming that the EAR cut-point method can be used in the assessment, the usual intake distribu- tion of the group should be positioned so that only 2â3 percent of the individu- als in the group have usual intakes less than the EAR. To achieve this goal of a low prevalence of nutrient inadequacy, it may be necessary to modify the baseline usual nutrient intake distribution. The change may be as simple as a shift (up or down) of the entire baseline distribution or it may include changes in both the location and the shape of the distribution. In either case, the appropriate changes to the baseline usual nutrient intake distribution are intended to result in the desired distribution of usual intakes. This desired distribution is referred to as the target usual nutrient intake distribution. The simplest approach to determining the target usual nutrient intake dis- tribution is to shift the baseline distribution, with the assumption that there will be no change in its shape. This is illustrated for a hypothetical nutrient in Figure 6. Panel A shows the baseline usual intake distribution, in which the prevalence of inadequate intakes (the percentage of the group below the EAR) is about 30 percent. If the planning goal were to attain a prevalence of inad- equacy of no more than 2â3 percent, the target usual nutrient intake distribu- tion could be achieved by simply shifting the baseline usual intake distribution up, as shown in Panel B. The appropriate shift (up or down) can be calculated as the additional (or decreased) amount of the nutrient that must be consumed to achieve the preva- lence of usual intakes below the EAR that is the planning goal. For example, the EAR for zinc for girls aged 9 to 13 years is 7 mg/day. Current data from the National Health and Nutrition Examination Survey (NHANES III, 1988â1994) show that about 10 percent of the girls have usual intakes below the EAR. If the goal were to plan intakes so that only 2â3 percent fell below the EAR, intakes would have to be increased. When the intervention is designed to increase everyoneâs usual zinc intake, then the amount of the increase can be calculated as the difference between the current intake at the second to third percentile, which is 6.2 mg/day, and the desired intake at the second to third percentile, which is the EAR of 7 mg/day. This difference is 0.8 mg/day, which means that the distribution of usual intakes needs to shift up by 0.8 mg/day in order to have only 2â3 percent of the girls with intakes below the EAR.
PART I: APPLYING THE DIETARY REFERENCE INTAKES 49 Panel A EAR Median Requirement Distribution Frequency Intake Distribution 30% Baseline Usual Intake Panel B EAR Median Requirement Distribution Intake Distribution Frequency 2.5% Target Usual Intake FIGURE 6 Concept of a target usual intake distribution. Panel A shows the baseline usual nutrient intake distribution with 30 percent prevalence of inadequate intakes. Panel B shows the effect of shifting the baseline distribution to attain the target usual nutrient intake distribution of 2â3 percent inadequate intakes. HOW TO ESTIMATE THE TARGET INTAKE DISTRIBUTION FOR GROUPS WITH NORMAL INTAKE DISTRIBUTIONS To set a target usual nutrient intake distribution with a selected prevalence of inadequacy for a specific group, it is useful to examine a simple example de- picting a normal distribution of usual intake. When it is known that the usual intake distribution of the group being assessed approximates normality, as depicted in all panels of Figure 7, the posi- tion of the target usual nutrient intake distribution can be estimated very sim- ply with a table of selected areas under the normal distribution. The median (midpoint) of the target usual intake distribution can be determined using the following equation: EAR + (Z Â¥ SDusual intake)
DRIs: THE ESSENTIAL GUIDE TO NUTRIENT REQUIREMENTS 50 Panel A Median of the Target EAR RDA Intake Distribution Frequency Requirement Distribution Intake Distribution 2.5% 50 65 86 Usual Intake Median of the Target Panel B Intake Distribution EAR RDA Frequency Requirement Distribution Intake Distribution 2.5% 101 50 65 86 Usual Intake Panel C RDA = Median of the Target Intake Distribution EAR Frequency Requirement Distribution Intake Distribution 28% 50 65 86 Usual Intake FIGURE 7 Target usual intake distributions. Panel A: Low group prevalence of inadequacy: 2.5 percent of the population has usual intake below the estimated average requirement. Panel B: Low individual risk of inadequacy: 2.5 percent of the population has usual intake below the RDA. Panel C: Higher group and individual risk of inadequacy: target median intake equals the RDA.
PART I: APPLYING THE DIETARY REFERENCE INTAKES 51 where Z comes from a table of areas under the curve of a normal distribution and SDusual intake is the standard deviation of the intake distribution. Table 3 reproduces part of a table of z-scores. For example, as shown in Panel of A of Figure 7, when the EAR is 50 units and the SDusual intakeis 18 units, a 2.5 percent prevalence of inadequacy (Z = 1.96 at 2.5 percent) would be expected when the median intake was 86 units (86 = 50 + [1.96 Â¥ 18]). On the other hand, if a 5 percent prevalence of inadequacy were chosen, the calculated median intake would be 80 (80 = 50 + [1.65 Â¥ 18]), a lower value since more of the group would have intakes below the EAR. HOW TO ESTIMATE THE TARGET INTAKE DISTRIBUTION FOR GROUPS WITH SKEWED INTAKE DISTRIBUTIONS The previous section described how to estimate a target distribution assuming a normal distribution of usual intakes within the group. However, in most cases, the usual intakes within a group are not normally distributed. Therefore, the SDusual intake cannot be used to identify the position of the target usual nutrient intake distribution. Instead, the necessary approach is similar in principle to the one in the previous section, although it does not depend on the SD of usual intake and a z-score. A practitioner would first specify the acceptable preva- lence of inadequate intake, and then position the usual intake distribution so TABLE 3 Setting the Target Median Intakea for Nutrients with Intake Distributions Approximating Normality: Selecting Z-Scores Acceptable Group Risk of Z-Score: Multiplier for the Inadequate Intakes (%) Standard Deviation of Intake 0.05 3.27 0.5 2.57 1.0 2.33 1.5 2.17 2.0 2.05 2.5 1.96 3.0 1.88 5.0 1.65 10.0 1.28 15.0 1.03 25.0 0.68 50.0 0.00 a Target median intake = EAR + Z Â¥ S D usual intake w here EAR = Estimated Average Requirement, Z = statistical tool to determine areas under the normal distribution, SD = standard deviation of intake.
DRIs: THE ESSENTIAL GUIDE TO NUTRIENT REQUIREMENTS 52 that the percentile of usual intake associated with this specified prevalence of inadequate intake equals the EAR. Using the DRIs to Plan a Groupâs Nutrient Intakes The summary below explains how DRIs are appropriately used in planning a groupâs nutrient intakes. Further details are provided in the sections that follow and in the case studies at the end of the chapter. â¢ For nutrients with an EAR and RDA, the EAR is used in conjunction with the usual nutrient intake distribution to plan for an acceptably low prevalence of inadequate intakes within the group. For most nutrients, the planning goal is to minimize the prevalence of intakes below the EAR. The RDA is not recommended for use in planning the nutrient intakes of groups. â¢ For nutrients without an EAR, the AI is used instead. The AI is used as the target for the mean, or median, intake of the group. The goal is to increase the groupâs mean or median intake to the level of the AI. â¢ For nutrients with a UL, this value is used to plan for an acceptably low prevalence of intakes at risk of being excessive. â¢ For nutrients with an AMDR, an additional goal of planning is to achieve a macronutrient distribution in which the intakes of most of the group fall within the AMDRs. â¢ For energy, the goal is for the groupâs mean intake to equal the EER. For energy, the estimated energy requirement of a reference individual or an average of estimated maintenance energy needs for the group members can be used in planning energy intake of groups. USING THE EAR TO PLAN A GROUPâS NUTRIENT INTAKES For nutrients that have an EAR, this value is used in conjunction with the usual nutrient intake distribution to plan for an acceptably low prevalence of inad- equate intakes within the group. For most nutrients, the planning goal is to minimize the prevalence of intakes below the EAR. USING THE AI TO PLAN A GROUPâS NUTRIENT INTAKES Due to limitations in available data, the AIs for various nutrients are set using different criteria. For some nutrients, the AI is based on the observed mean or median intakes by groups that are maintaining health and nutritional status consistent with meeting requirements. In these cases, the AI is conceptually similar to the median of a target usual nutrient intake distribution. For other nutrients, the AI is the level of intake at which subjects in an experimental
PART I: APPLYING THE DIETARY REFERENCE INTAKES 53 TABLE 4 Method Used to Estimate Adequate Intake (AI) for Groups of Healthy Adults Estimation Method Nutrient Experimental derivation Biotin Calcium Choline Vitamin D Fiber, total Fluoride Potassium Sodium and chloride Mean intake Chromium Median intake Vitamin K Manganese Pantothenic acid n-6 Polyunsaturated fatty acids n-3 Polyunsaturated fatty acids Water, total study met the criterion of adequacy. In these cases, the AI is not directly compa- rable to a target median intake. Because of these differences in how the AI is set for different nutrients, the appropriate use of the AI in planning group intakes also varies. The AI can be used if the variability in the usual intake of the population being planned for is similar to the variability in intake of the healthy population that was used to set the AI. In this case, the appropriate use of the AI would be as the target median intake of the group. However, if the AI is not based on a group mean or median intake of a healthy population, practitioners must recognize that there is a reduced level of confidence that achieving a mean or median intake at the AI will result in a low prevalence of inadequacy. In addition, the AI cannot be used to estimate the proportion of a group with inadequate intakes. Thus, regardless of how the AI has been estimated, it is not possible to use the AI to plan a target distribution of usual intakes with a known prevalence of inadequacy. Table 4 presents a summary of the nutrients for which AIs have been estimated and notes the cases in which these estimates reflect experimental derivation and observed
DRIs: THE ESSENTIAL GUIDE TO NUTRIENT REQUIREMENTS 54 mean and median intake of healthy groups. Practitioners who want to compare their target groups to the groups used to set the AIs can obtain this information in each of the individual nutrient profiles found in Part III. USING THE UL TO PLAN A GROUPâS NUTRIENT INTAKES For nutrients that have a UL, the planning goal is to achieve an acceptably low prevalence of intakes above the UL. USING THE EER TO PLAN A GROUPâS DIET As is true for individuals, the underlying objective in planning the energy in- take of a group is similar to planning intakes for other nutrients: to attain an acceptably low prevalence of inadequacy and potential excess. When planning the energy intakes of groups, the goal is for the groupâs mean intake to equal the EER. Because energy intake is related to energy requirement, it is assumed that people in the group with energy requirements above the EER will choose en- ergy intakes that are above the EER, and those with requirements below the EER will choose intakes below the EER, so that the average intake will equal the EER. The EAR cut-point approach should not be used for planning energy in- takes, because it is expected, and desirable, for half of the group to have intakes below the EER. There are two possible approaches to estimate energy intakes of groups. One can estimate energy requirements for the reference person or obtain an average of estimated maintenance energy needs for the group members. For example, to plan for a large group of men aged 19 through 30 years, one can estimate the EER for the reference male with a weight of 70 kg (154 lbs) and a height of 1.76 m (~ 5 ft 8 in) and who is considered low active, and use this number (~ 2,700 kcal) as the target for the group. This approach would re- quire the assumption that all members of the group were similar to the refer- ence person or that the reference person accurately represented the groupâs average values for age, height, weight, and activity level, and that these vari- ables were symmetrically distributed. The preferred approach would be to plan for an intake equal to the average energy expenditure for the group. For example, assuming that there is access to data on height, weight, age, and activity level, the energy expenditure for each individual in the group could be estimated. The average of these values would then be used as the planning goal for the maintenance of the groupâs current weight and activity level. As with other planning applications, assessing the plan for a groupâs energy intake, following its implementation, would lead to further refinements. In the case of energy, however, assessment would be based on monitoring body weight rather than on reported energy intake.
PART I: APPLYING THE DIETARY REFERENCE INTAKES 55 CASE STUDIES Case Study One: Using the Probability Approach to Assess Intakes in a Group Using a group of 650 adult men aged 19 to 30 years and a hypothetical nutrient with an EAR of 7 mg/day for this age and gender group illustrates the probabil- ity approach. Individuals in this group, even though they are similar in age and gender, differ in both their requirements for the nutrient and their usual intakes of the nutrient. At a conceptual level, determining the prevalence of inadequate nutrient intakes in the group would simply involve comparing each individualâs usual nutrient intake with his individual requirement, and totaling the number of men with usual intakes below their individual requirements. For example, a man with a usual nutrient intake of 9 mg/day and a requirement of 10 mg/day would not meet his requirement and would be classified as inadequate, whereas another man with a usual nutrient intake of 9 mg/day and a requirement of 5 mg/day would exceed his requirement. In practice, however, we almost never know individualsâ nutrient requirements. Instead, we may have information on the distribution of requirements for a small group of individuals who are simi- lar in age and gender, and who took part in studies to determine nutrient re- quirements. From that information, we can determine the probability, or risk, that a given intake will be adequate or inadequate. Knowledge of the distribution of requirements allows one to construct a risk curve that defines the probability that any given intake is inadequate, whether the requirement distribution is statistically normal or not. Figure 8 shows a risk curve for the example nutrient with an EAR of 7 mg/day. The requirement dis- tribution for this nutrient is statistically normal, and the SD is ~ 1.5 mg/day. As described earlier, for nutrients with normal requirement distributions, 95 per- cent of individuals have requirements within Â± 2 SD of the EAR. In this ex- ample, 95 percent of men aged 19 to 30 years would have requirements be- tween 4 mg/day (7 mg/day minus twice the SD of 1.5 mg/day) and 10 mg/day (7 mg/day plus twice the SD of 1.5 mg/day). The probability of inadequacy associated with any intake can be determined by assessing where the intake level intersects the risk curve. As illustrated in Figure 8, the probability of inadequacy at a usual intake at or below about 3 mg/day is associated with a probability of inadequacy of 1.0 (100 percent), meaning that virtually everyone with a usual intake in this range does not meet their own requirement. When usual intakes are at or above about 11 mg/day, the probability of inadequacy is zero, meaning that virtually every- one with a usual intake in this range would meet their own requirement. When usual intake is between 4 mg/day and 10 mg/day, the probability of inadequacy varies, and can be estimated by determining where the usual intake level inter- sects the risk curve:
DRIs: THE ESSENTIAL GUIDE TO NUTRIENT REQUIREMENTS 56 1.2 5 mg/d 1.0 Probability = 0.9 0.8 Probability of Inadequacy 0.6 7 mg/d (EAR) Probability = 0.5 0.4 0.2 9 mg/d Probability = 0.1 0 1 2 3 4 5 6 7 8 9 10 11 12 13 Usual Intake (mg/d) FIGURE 8 Risk curve. This risk curve is from a normal requirement distribution with a mean of 7 mg/day and a SD of 1.5 mg/day. â¢ It is relatively high at intakes that are just above the lower end of the distribution of requirements (about 0.9 or 90 percent at a usual intake of 5 mg/day in this example). â¢ By definition, the probability of inadequacy at the EAR is 0.5 or 50 percent (7 mg/day in this example). â¢ It is relatively low at intakes that are closer to the upper end of the distribution of requirements (about 0.1 or 10 percent at a usual intake of 9 mg/day in this example). The information on the probability of inadequacy of different usual intake levels is used to estimate the prevalence of inadequate intakes in the group. This is done by determining the probability of inadequacy for each usual intake level in the group, and then computing the average for the group as a whole. Figure 9 and Table 5 illustrate this approach. Figure 9 shows the risk curve from Figure 8, as well as a usual intake distribution for the group of 650 men in the example (each âboxâ in the figure represents 10 men and there are 65 boxes). Table 5 shows the usual intake levels from the distribution shown in Figure 9, the associated probability of inadequacy, and the number of men at that intake level.
PART I: APPLYING THE DIETARY REFERENCE INTAKES 57 1.2 Usual Intake Distribution Risk Curve 1.0 Probability of Inadequacy 0.8 0.6 0.4 0.2 0 1 2 3 4 5 6 7 8 9 10 11 12 13 Usual Intake (mg/d) FIGURE 9 Comparison of the risk curve to a usual intake distribution. In this simplified usual intake distribution, each âboxâ represents 10 men aged 19 to 30 years. The prevalence of inadequate intakes in the group is estimated by determining the probability of inadequacy associated with each individual usual intake level, and then calculating the average probability. To illustrate how Figure 9 and Table 5 work to determine the prevalence of inadequacy, consider men with intakes of 5 mg/day and 9 mg/day. Twenty men have usual intakes of 5 mg/day, and an intake of 5 mg/day intersects the risk curve at a probability of inadequacy of 0.90. Because each individual with a usual intake of 5 mg/day has a 90 percent (0.9) probability of being inadequate, one would expect 18 of 20 men (90 percent) to be inadequate. In contrast, 80 men have usual intakes of 9 mg/day, and an intake of 9 mg/day intersects the risk curve at a probability of inadequacy of 10 percent. One would thus expect 8 men (10 percent of the 80 men with usual in- takes of 9 mg/day) to be inadequate. The average probability of inadequacy is calculated by totaling the number of individuals likely to have inadequate in- takes, and then dividing by the total number of men. (This is mathematically identical to adding up all the individual probabilities of inadequacy [i.e., 1.0 + 1.0 + 1.0 + . . . + 0 + 0 + 0] and dividing by the total number of men.) In this example, the group prevalence of inadequacy is approximately 20 percent.
DRIs: THE ESSENTIAL GUIDE TO NUTRIENT REQUIREMENTS 58 TABLE 5 Using the Probability Approach to Estimate Group Prevalence of Inadequacy in a Group of 650 Adult Men Ages 19 to 30 Years for a Nutrient with an EAR of 7 mg/day Probability Â¥ Usual Intake Level Probability of Number of Numbera (mg/day) Inadequacy People 2 1.0 10 10 3 1.0 10 10 4 0.97 20 19.4 5 0.90 20 18.0 6 0.73 30 21.9 7 0.50 50 25.0 8 0.27 60 16.2 9 0.10 80 8.0 10 0.03 100 3.0 11 0 100 0 12 0 80 0 13 0 60 0 14 0 30 0 Total 650 131.5 = probability Â¥ number/total Average probability = 131.5/650 = 0.20 (20 percent) a This represents the number of men expected to have inadequate intakes at each intake level. Case Study Two: Using the Probability Approach to Assess Iron Intakes in a Group of Menstruating Women The probability approach involves first determining the risk of inadequacy for each individual in the population, and then averaging the individual probabili- ties across the group. For iron, Appendix Tables G-5, G-6, and G-7 give the probability of inadequacy at various intakes. These tables may be used to calcu- late the risk of inadequacy for each individual, and then the estimated preva- lence of inadequacy for a population. In addition, Appendix C of the original report titled, Dietary Reference Intakes: Applications in Dietary Assessment (2000), demonstrates how to carry out the necessary calculations to obtain a prevalence estimate for a group. This case study presents a simplified estimate that could also be deter- mined manually. The estimate is illustrated in Table 6 for a hypothetical group of 1,000 menstruating women not taking oral contraceptives and consuming a
PART I: APPLYING THE DIETARY REFERENCE INTAKES 59 typical omnivorous diet. The first and second columns of this table are based on information in Appendix Tables G-4 and G-7. Intakes below 4.42 mg/day are assumed to have a 100 percent probability of inadequacy (risk = 1.0). Indi- viduals with intakes above 18.23 mg/day are assumed to have a zero risk of inadequacy. For intakes between these two extremes, the risk of inadequacy is calculated as 100 minus the midpoint of the percentile of requirement. For example, intakes between 4.42 and 4.88 fall between the 2.5 and 5th percentile of requirement. The midpoint is 3.75, and the probability of inadequacy is 100 â 3.75 Âª 96.3 percent, or a risk of 0.96. The appropriate risk of inadequacy is then multiplied by the number of women with intakes in that range. In this case study, only one woman had an intake between 4.42 and 4.87 mg/day, so the number of women with inadequate intake is 0.96 (1 Â¥ 0.96). In the next range (4.88 mg/day to 5.46 mg/day, or between the 5th and 10th percentiles) there were three women, with an associated number of women with inadequate intake of 2.79 (3 Â¥ 0.93). If this is done for each intake range, the total number of women with inadequate intakes can be determined. In this example, 165 of the 1,000 women have inadequate intakes, for an estimated prevalence of inad- TABLE 6 Illustration of the Full Probability Approach to Estimate the Prevalence of Dietary Iron Inadequacy in a Group of 1,000 Menstruating Women (Not Using Oral Contraceptives and Following an Omnivorous Diet) Range of Usual Percentiles of Intake Associated Probability Number of Number of Requirement with Requirement of Women with Women with Distribution Percentiles (mg/day) Inadequacy Intake in Range Inadequate Intake < 2.5 < 4.42 1.0 1 1 2.5â5.0 4.42â4.88 0.96 1 0.96 5â10 4.89â5.45 0.93 3 2.79 10â20 5.46â6.22 0.85 10 8.5 20â30 6.23â6.87 0.75 15 11.25 30â40 6.88â7.46 0.65 20 13 40â50 7.47â8.07 0.55 23 12.65 50â60 8.08â8.76 0.45 27 12.15 60â70 8.77â9.63 0.35 50 17.5 70â80 9.64â10.82 0.25 150 37.5 80â90 10.83â13.05 0.15 200 30.0 90â95 13.06â15.49 0.08 175 14 95â97.5 15.50â18.23 0.04 125 5 > 97.5 > 18.23 0.0 200 0 Total 1,000 165
DRIs: THE ESSENTIAL GUIDE TO NUTRIENT REQUIREMENTS 60 equacy of 16.5 percent. It is important to remember that this approach does not identify the specific women with inadequate intakes, but is rather a statistical calculation of the prevalence of inadequate intakes. Thus, it cannot be used to screen individuals at risk of inadequacy. Note that the prevalence of nutrient inadequacy that is estimated by the full probability approach differs considerably from that estimated by the cut- point method (the proportion with intakes below the EAR). In this example, the EAR (median requirement) is 8.07 mg/day, and only 73 women have in- takes below this amount. Thus, the cut-point method would lead to an esti- mated prevalence of inadequacy of 7.3 percent, which differs considerably from the estimate of 16.5 percent obtained by using the full probability approach. The reason for the discrepancy is that one of the conditions needed for the cut- point approach (a symmetrical requirement distribution) is not true for iron requirements of menstruating women. Case Study Three: Using the EAR Cut-Point Method The EAR cut-point method is illustrated in Figure 10, which shows a hypo- thetical joint distribution of usual intakes and individual requirements for a group of 60 individuals. This example is hypothetical because in practice we almost never have access to accurate data on either usual intakes of individuals or their individual requirements. Figure 10 includes a 45â dashed line labeled âIntake = Requirement.â Individuals who fall to the right of and below this line have usual intakes that exceed their individual requirements (i.e., they have adequate intakes), whereas individuals who fall to the left of and above the line have usual intakes that do not meet their requirements (i.e., they have inad- equate intakes). Determining the prevalence of inadequacy in this hypothetical situation is easy: one simply counts the number of individuals with usual in- takes below their individual requirements. In this example, 13 individuals have intakes to the left of and above the âIntake = Requirementâ line, so the group prevalence of inadequacy is 13/60, or 21.7 percent. Figure 10 also shows the EAR (in this example, it is 4 mg/day) on both the requirement axis (the Y axis) and the usual intake axis (X axis). Focusing on the X axis, note that most individuals with usual intakes below the EAR have inad- equate intakes (they are to the left of and above the âIntake = Requirementâ line), but that some (who appear in the triangle labeled 1) have usual intakes that exceed their individual requirements. Similarly, although most individuals with usual intakes above the EAR meet their requirements (they are to the right of and below the âIntake = Requirementâ line), some (who appear in the tri- angle labeled 2) do not.
PART I: APPLYING THE DIETARY REFERENCE INTAKES 61 8 EAR Intake = Requirement 2 7 Intake < Requirement 6 Requirement (mg/d) 5 EAR 4 3 2 Intake > Requirement 1 1 0 0 2 4 6 8 10 12 Usual Intake (mg/d) FIGURE 10 Joint distribution of requirements and usual intakes. Individuals with usual intakes below their individual requirements are found to the left of and above the dashed 45o line labeled Intake = Requirement. When assumptions for the EAR cut-point method are satisfied, this proportion of the group is mathematically similar to the proportion to the left of the vertical EAR line. The assumptions required for use of the EAR cut-point method are satis- fied in this example, as described below: 1. Requirement distribution is approximately symmetrical. In Figure 10, it can be seen that similar proportions of the group have requirements above and below the EAR of 4 mg/day (the number of individuals above the horizontal EAR line is similar to the number of individuals below). 2. Intakes and requirements are independent. Figure 10 shows that indi- viduals with low requirements are just as likely as individuals with high requirements to have high (or low) usual intakes. 3. The usual intake distribution is more variable than the requirement dis- tribution. In Figure 10, it can be seen that there is more variability in the intake distribution (it ranges from less than 2 mg/day to almost 10 mg/ day) than in the requirement distribution (which ranges from about 2 mg/day to about 6 mg/day).
DRIs: THE ESSENTIAL GUIDE TO NUTRIENT REQUIREMENTS 62 When the above conditions are met, the individuals in triangle 1 (with intakes below the EAR but above their own requirements) are similar in number to the individuals in triangle 2 (with intakes above the EAR and below their own requirements). These two triangles cancel one another out, and the number of individuals that do not meet their requirements (those found to the left of the 45o âIntake = Requirementâ line) is thus mathematically similar to the number with usual intakes below the EAR. The EAR cut-point method can also be applied to the example of 650 men described in the first case study, as the requirement distribution is symmetrical, intakes and requirements are independent, and the usual intake distribution is more variable than the requirement distribution. In this case, one would simply determine the number of men with intakes at or below the EAR of 7 mg/day. From Table 5, this would be 10 (2 mg/day) + 10 (3 mg/day) + 20 (4 mg/day) + 20 (5 mg/day) + 30 (6 mg/day) + 50 (7 mg/day), for a total of 140 men. Divid- ing this by the total group size of 650 yields the estimated prevalence of inad- equacy of 21.5 percent, which is very similar to the estimate of 20 percent obtained using the full probability method. In summary, the full probability method and a shortcut, known as the EAR cut-point method, can be used to estimate the prevalence of nutrient inad- equacy in a group. Both methods require knowledge of the distribution of usual intakes for the group, and that intakes and requirements are independent. The EAR cut-point method has two additional requirements; namely, that the re- quirement distribution is symmetrical, and that the distribution of usual in- takes is more variable than the distribution of requirements. If either of these two additional requirements is not met, the full probability method can be used instead, provided the requirement distribution is known. Case Study Four: Planning Diets in an Assisted-Living Facility for Senior Citizens An example of planning diets for institutionalized groups is menu planning for senior citizens who reside in an assisted-living facility. Menus planned for these institutions usually assume that the residents have no other sources of foods or nutrients, and thus the menus are designed to meet all nutrient needs of the residents. The goal of menu planning is to provide meals that provide adequate nutrients for a high proportion of the residents, or conversely, the prevalence of inadequate intakes is acceptably low among the residents. The planner is developing a menu for an assisted living facility in which the residents are retired nuns aged 70 years and above. For this age group, the EAR for vitamin B6 is 1.3 mg/day. Assume that no data can be located on the distribution of usual intakes of this group or a similar group, and that resources are not available to conduct a dietary survey in the institution. How could the
PART I: APPLYING THE DIETARY REFERENCE INTAKES 63 planner proceed to determine the target intake distribution of vitamin B6 needed to attain an acceptable prevalence of inadequacy? STEP 1. DETERMINE AN ACCEPTABLY LOW PREVALENCE OF INADEQUACY For vitamin B6, the EAR was set at a level adequate to maintain plasma pyri- doxal phosphate levels at 20 nmol/L. This plasma level is not accompanied by observable health risks, and thus allows a moderate safety margin to protect against the development of signs or symptoms of deficiency. This cut-off level was selected recognizing that its use may overestimate the B6 requirement for health maintenance of more than half the group. For this reason, assume that the planner has determined that a 10 percent prevalence of inadequacy (i.e., 10 percent with intakes below the EAR) would be an acceptable planning goal. STEP 2. DETERMINE THE TARGET USUAL NUTRIENT INTAKE DISTRIBUTION Next, the planner needs to position the intake distribution so the nutrient in- take goals are met. In this example, the planner decides that the prevalence of inadequacy in the group will be set at 10 percent, and as a result the usual intake distribution of the group should be positioned such that only 10 percent of the group has usual intakes less than the EAR. Because data on the usual nutrient intake distributions of the residents are not available, other sources must be used to estimate the target usual nutrient intake distribution. Data on the distribution of usual dietary intakes of vitamin B6 are available from several national surveys and thus are used. The adjusted percentiles for women are summarized in Table 7. Assuming there are no changes in the shape of the distribution, the amount of the shift can be calculated as the additional amount of the nutrient that must be consumed to reduce the proportion of the group that is below the EAR. This is accomplished by determining the difference between the EAR and the intake at the acceptable prevalence of inadequacy (in this case, the 10th percentile of the usual intake distribution). TABLE 7 Selected Percentiles of the Distributions of Usual Intake of Vitamin B 6 from Foods in Older Women Percentile of Usual Intake Distribution of Vitamin B6 (mg/day) Study n 5th 10th 25th 50th 75th 90th 95th Survey A 1,368 0.92 1.04 1.24 1.53 1.93 2.43 2.76 Survey B 221 0.76 0.88 1.11 1.41 1.76 2.12 2.35 Survey C 281 0.5 0.6 0.7 1.0 1.3 1.6 1.8
DRIs: THE ESSENTIAL GUIDE TO NUTRIENT REQUIREMENTS 64 TABLE 8 Identification of the Target Median Intakea of Vitamin B 6 to Obtain a 10 Percent Prevalence of Inadequacy in Older Women Intake Difference Target at 10th (EAR â intake Median Median EAR Percentile at 10th Intake Intake Study (mg/day) (mg/day) percentile) (mg/day) (mg/day) Survey A 1.3 1.04 0.26 1.53 1.79 Survey B 1.3 0.88 0.42 1.41 1.83 Survey C 1.3 0.6 0.7 1.0 1.70 a The target median intake is estimated by adding the difference between the Estimated Average Requirement (EAR) and the intake at the acceptable prevalence of inadequacy (in this case, 10 percent) to the observed median intake. Examination of the data from the three surveys shows that estimated usual intakes of vitamin B6 vary by as much as 30 percent among the surveys. As a result, the difference between the EAR of 1.3 mg and the intake at the 10th percentile varies, depending on which data are used. Table 8 shows that for Survey A the difference is 0.26 mg (1.3 mg â 1.04 mg = 0.26 mg); for Survey B, the difference is 0.42 mg (1.3 mg â 0.88 mg = 0.42 mg); and for Survey C, the difference is 0.7 mg (1.3 mg â 0.6 mg = 0.7 mg). In this example, the planner may have no reason to choose data from one particular survey as âmore appli- cableâ to the group than another, so he may estimate target usual nutrient in- take distributions using all three data sets. Accordingly, the target intake distri- butions shift up by 0.26 mg, by 0.42 mg, and by 0.7 mg. using Survey A, B, or C. In each case the target usual nutrient intake distribution would lead to the accepted prevalence of inadequacy. Rather than choosing one set of survey data over another, the planner could simply average the summary measures described in the next section. STEP 3. SELECT A SUMMARY MEASURE OF THE TARGET USUAL NUTRIENT INTAKE DISTRIBUTION TO USE IN PLANNING After the planner has estimated a target usual intake distribution, then this information needs to be operationalized into a menu. In order to do this, the planner will first have to select a summary measure of the target usual nutrient intake distribution to use as a tool in planning the menu. The median of the target intake distribution is the most useful; it can be calculated as the median of the current intake distribution, plus (or minus) the amount that the distribu- tion needs to shift to make it the target usual intake distribution. In the current example, although the baseline intakes at the 10th percen- tile and the median differ among the three surveys, the estimates of the medians
PART I: APPLYING THE DIETARY REFERENCE INTAKES 65 of the target usual intake distributions are quite similar, as shown in Table 8. Assuming that a 10 percent prevalence of intakes below the EAR was consid- ered acceptable, a median intake for vitamin B6 of 1.7 to 1.8 mg/day would be the planning goal. Accordingly, the menu would need to be planned so that vitamin B6 intakes would be at this level. Estimates of target nutrient intakes must be converted to estimates of foods to purchase, offer, and serve that will result in the usual intake distributions meeting the intake goals. This is not an easy task. Meals with an average nutri- ent content equal to the median of the target usual nutrient intake distribution may not meet the planning goals, as individuals in a group tend to consume less than what is offered and served to them. Thus, the planner might aim for a menu that offers a choice of meals with a nutrient content range that includes, or even exceeds, the median of the target usual nutrient intake distribution. STEP 4. ASSESS IMPLEMENTATION OF THE PLAN Ideally, after the menu had been planned and implemented, a survey would be conducted to assess intakes and determine whether the planning goal had been attained. This would then be used as the basis for further planning. KEY POINTS FOR WORKING WITH GROUPS ASSESSING NUTRIENT INTAKES The goal of assessing nutrient intakes of groups is to determine 3 the prevalence of inadequate (or excessive) nutrient intakes within a particular group of individuals. Assessment of groups should always be performed using 3 intakes that have been adjusted to represent a usual intake distribution. The probability approach and the EAR cut-point method are 3 two statistical methods of determining the prevalence of inadequacy in a group. The EAR cut-point method is a simpler method derived from the probability approach. For nutrients in which it is appropriate to do so, the EAR can be 3 used as part of the EAR cut-point method to determine the prevalence of nutrient inadequacy within a group. Otherwise, the probability approach can be used. The AI has limited application in assessing a groupâs nutrient 3 intakes. For nutrients with an appropriately estimated AI, groups with mean or median intakes at or above the AI can generally be assumed to have a low prevalence of inadequate intakes.
DRIs: THE ESSENTIAL GUIDE TO NUTRIENT REQUIREMENTS 66 The UL can be used to estimate the proportion of a group at 3 potential risk of adverse effects from excessive nutrient intakes. The RDA should not be used in the assessment of a groupâs 3 nutrient intakes. Comparing mean or median intake with the RDA is inappropriate. To assess the energy adequacy of an individual or group diet, 3 information other than self-reported intakes should be used because underreporting of energy intake is a serious and pervasive problem. Body weight for height, BMI, or other anthropometric measures are suitable for use in assessing long-term energy intake. PLANNING NUTRIENT INTAKES The goal of planning nutrient intakes for groups is to achieve 3 usual intakes that meet the requirements of most individuals, but that are not excessive. The DRIs present an approach to planning that involves 3 consideration of the entire distribution of usual nutrient intakes within a group. The basic steps in planning for groups are as follows: First the 3 practitioner decides on an acceptable prevalence of inadequacy. The distribution of usual intakes in the group must then be estimated using the distribution of reported or observed intakes. Finally, a target usual intake distribution is determined by positioning the distribution of usual intakes relative to the EAR to achieve the desired prevalence of inadequacy. For nutrients with an EAR, the planning goal is to aim for an 3 acceptably low prevalence of intakes below the EAR. The RDA is not recommended for use when planning nutrient 3 intakes of groups. For nutrients with an AI, this value is used as the target for the 3 mean or median intake when planning for groups. For nutrients with a UL, the planning goal is to achieve an 3 acceptably low prevalence of intakes above the UL. When planning a groupâs energy intake, the goal is for the 3 groupâs mean intake to equal the EER.
PART I: APPLYING THE DIETARY REFERENCE INTAKES 67 SUMMARY The DRI values can be used by nutrition professionals to assess and plan the nutrient intakes of individuals and of groups. Table 9 summarizes the chapter discussions on the appropriate uses of each of the DRI values to achieve these goals.
DRIs: THE ESSENTIAL GUIDE TO NUTRIENT REQUIREMENTS 68 TABLE 9 Using the DRIs to Assess and Plan the Nutrient Intakes of Individuals and Groups EAR RDA AI UL When Assessing Diets For individuals: Usual intake Not recommended Usual intake at Usual intake above below the EAR for use when or above the AI the UL may place an likely needs to assessing nutrient has a low individual at risk of be improved. The intakes of probability of adverse effects. probability of individuals. inadequacy. adequacy is 50 percent or less. For groups: Used as part of Not used when Limited Used to estimate the the EAR cut-point assessing nutrient application. proportion of a group method to intakes of groups. Groups with mean at potential risk of determine the or median intakes adverse effects from prevalence of at or above the excessive nutrient nutrient AI can generally intake. inadequacy within be assumed to a group. have a low prevalence of inadequate intakes. When Planning Diets For individuals: Intake at EAR Low probability of Intakes at AI will Low probability of has 50 percent inadequate intake likely meet or adverse effects from probability of not at RDA. Therefore, exceed an excessive meeting often used as a individualâs consumption so requirement. guide. requirement. average intake should not exceed the UL. For groups: Aim for an Not used when Use as a target Aim for an acceptably low planning the for the mean or acceptably low prevalence of nutrient intakes median intake. prevalence of intakes intakes below of groups. above the UL. the EAR.