Dietary Reference Intakes Applications in Dietary Assessment (2000) / Chapter Skim
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3 Using Dietary Reference Intakes for Nutrient Assessment of Individuals
3 Using Dietary Reference Intakes for Nutrient Assessment of Individuals
Pages 45-70
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From page 45... ...
Although the information presented in this chapter focuses on nutrient intake data, it should always be considereci in combination with other information in clietary assessment of inclivicluals. Throughout the chapter, the fact that an incliviclual's observed mean intake over a few clays may not be an accurate estimate of that incliviclual's usual intake is emphasized.
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From page 46... ...
is not recommended for individual assessment. Whether one is interested in assessing the acloquacy of the incliviclual's usual intake or in clecicling whether usual intake exceeds the UL, the relevant information must include both the observed mean intake and the stanciarci deviation (8D)
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From page 47... ...
For some nutrients, however, it is possible to approximately assess whether an incliviclual's nutrient intake meets his or her requirement. The remainder of this chapter and Appendix B provide specific guidance to help professionals assess individual dietary intake ciata relative to the DRIB.
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From page 48... ...
, and the large ciayto-ciay variation in intake (Beaton et al., 1979, 1983; Gibson, 1990; Sempos et al., 1985; Tarasuk and Beaton,199lb, 1992; Van Staveren et al., 1982~. Intake on one or even several clays may give very inaccurate estimates of usual intake, especially if the incliviclual's food choices vary greatly from one clay to the next, which is a common occurrence.
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From page 49... ...
, this observed intake is probably not the same as long-term usual intake. In all likelihood, an incliviclual's observed intake cluring one 3-clay period will differ from observed intake in another 3-clay period, and both 3-clay observed intakes will differ from true usual intake.
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From page 50... ...
A pooled estimate of the within-person variability in intakes has been computed for a number of nutrients from nationwide food consumption surveys (see Appendix Tables B-2 through Bed. The magnitude of the ciay-to-ciay variation in intakes of a nutrient will indicate whether the observed mean intake calculated from a few ciaily records or recalls is a more or less precise estimator of the incliviclual's usual intake of that nutrient.
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From page 51... ...
, it may be used in a more limited way as clescribeci in the next section. Interpret Individua;t Dietary Intake Data The third step in incliviclual assessment is to assess the ciata to answer the question, On the basis of an incliviclual's observed intake over a small number of days, is that individual's usual intake of the nutrient adequate and at low risk of adverse effects?
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From page 52... ...
That is, D is the difference between the mean observed intake for an individual ~ y ~ and the median requirement (EAR, called r for simplicity) for the life stage and gender group to which the individual belongs, D= y-r.
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From page 53... ...
Intuitively, as the number n of intake days available on the individual increases, the variance of the observed mean intake should decrease (i.e., the accuracy of the estimate for y increases)
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From page 54... ...
SD of daily intake. Why not use the woman's three clays of intake records to estimate her SD of ciaily intake?
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From page 55... ...
Baseci on the SD in intake of 85.9 mg/ciay for an incliviclual (again using the information in Appendix Table B-2) , observed intake would neeci
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From page 56... ...
However, a mean observed intake of only 349 mg/ciay (109 percent of the RDA) would be neecleci with 7 clays of observed intake.
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From page 57... ...
Thus, for practical purposes, many users of the DRIs may finci it useful to consider that observed intakes below the EAR very likely neeci to be improved (because the probability of acloquacy is 50 percent or less) , and those between the EAR and the RDA probably neeci to be improved (because the probability of acloquacy is less than 97.5 percent)
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From page 58... ...
. · The incliviclual's intake is unclerreporteci, so that the mean observed intake is a biased estimator of the incliviclual's usual intake.
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From page 59... ...
The approach cliscusseci previously to assess nutrient acloquacy compares an incliviclual's observed intake to the EAR, and considers variability in both intakes and requirements when determining how confident one can be in concluding that an incliviclual's intake is acloquate. In other words, intakes are compared to the median requirement.
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From page 60... ...
This procedure, therefore, can be used to determine whether usual intake is larger than the AI given the observed intake for a few clays. Given an observed mean intake for the incliviclual the confidence with which one can determine usual intake to be above the AI clepencis on: ( 1 )
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From page 61... ...
) 1 d of intake 0.61 0.49 0.41 3 d of intake 1.07 0.85 0.71 7 d of intake 1.69 1.30 1.08 Percentage confidence that the woman's usual intake exceeds the AId 1 d of intake 73 69 3 d of intake 86 80 7 d of intake 9 5 9 0 66 76 86 NOTE: The confidence with which one can conclude that usual intake is greater than the AI decreases when the number of days of daily intake records for the individual decreases, or when the SD of daily intake increases.
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From page 62... ...
In those cases, a qualitative interpretation of the observed mean intake may be all that is available. Table 3-3 gives some guidance on to how to interpret mean observed intake relative to the AI qualitatively.
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From page 63... ...
A test similar to the one clescribecT in the prececling section for the AI can be implemented to clecicle whether usual intake is below the UL given the observed mean intake. The test is constructed in exactly the same manner, but now the UL is subtracted from the mean observed intake for the incliviclual.
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From page 64... ...
From the example in Table 3-4, it can be seen that even when observed mean intake is less than the UL, sometimes it cannot be conclucleci with clesireci accuracy that usual intake is also below the UL. When only one clay of intake ciata is available for the incliviclual, one would have only between 63 and 69 percent (depending on the SD of daily intake)
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From page 65... ...
Since this test would be conclucteci only in cases where the observed mean intake for the incliviclual is high enough to suggest a problem, the SD of ciaily intake as calculated in CSFII or the National Health and Nutrition Examination Survey may underestimate the incliviclual's true SD of ciaily intake. This is because there is some evidence that the SD of ciaily intake increases as the mean intake increases (Nusser et al., 1996~.
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From page 66... ...
In these cases, the proposed methods are even less reliable, as currently there are no estimates of the within-person stanciarci deviation of intakes from supplement use alone. APPLICATIONS The following examples show how the Dietary Reference Intakes (DRIB)
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From page 67... ...
T wants to know whether her cliet is optimal. Assessment With the caveat that 7 clays is not long enough to provide accurate information on her usual nutrient intake, her mean observed intake can be evaluated relative to the DRIB.
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From page 69... ...
can be used in assessment of the apparent acloquacy or excess of an incliviclual's clietary intake. Such an assessment requires using the incliviclual's observed mean intake as an estimate of long-term usual intake and using the Estimateci Average Requirement (EAR)
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From page 70... ...
These weights must be carried throughout the procedure for estimating usual intake distributions if this estimated distribution is to be used to make inferences about the wider population from which the group was drawn. Overview of Methods to Adjust Mean Intake Distributions Because of the above attributes of dietary intake data, obtaining reliable estimates of usual intake distributions is not straightforward.
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