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Introduction
Since 1936, the USDA has conducted six national surveys
of food consumption at roughly 10-year intervals. The
early surveys measured disappearance of food from household
supplies but not individual intake; however, in 1956 the
protocol was changed to include individual data on recall
of foods consumed over a 24-hour period. The latest
Nationwide Food Consumption Survey (NFCS), conducted in
1977-1978, included both household and individual compo-
nents. It included a recall of foods consumed by individ-
uals at home and away from home d',ring a 3-day period.
The survey did not include questions on nutrient supple-
ments. The data were collected through face-to-face
interviews during which individual household members were
asked to report their food intake over the previous 24
hours. The respondents were then given a food diary to
record their intake over the next 2 days. his individual
intake component consisting of a 1-day recall and 2-day
record for each individual is the basis for USDA analyses
of the nutritive value of foods consumed in the United
States (Peterkin _ al., 1982). These data have been
reported by se.:, age, region of residence, income, race,
and household characteristics (Pao et al.. 1982).
For some years, the USDA used the recommended dietary
allowances (RDAs) (NRC, 1980) to evaluate the adequacy
of nutrient intake. However, the RDAs do not represent
the true requirement of all persons. Rather, they in-
clude a margin of safety to allow for variability and
other factors. Therefore, the USDA staff and other
food-consumption analysts have traditionally defined
inadequate intake as intake below a fixed cutoff point.
Some analysts use two-thirds of a specific RDA as a
definition of inadequate intake; others use one-half or
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three-fourths of the RDA (Peterkin et al., 1982). There
have been criticisms of this approach, and no clear
rationale for the selection of the particular cutoff point
has emerged.
Nutritional status cannot be determined from data on
dietary intake alone. If appropriate criteria are used,
however, these data can be used for making a preliminary
evaluation of the proportion of the population that may
be at risk for impaired nutritional status.
The task of the Subcommittee on Dietary Intake
Evaluation was to develop criteria and approaches for
interpreting the nutrient intake information in the
Nationwide Food Consumption Survey (NFCS). Specifically,
it was asked to develop criteria for using survey data on
dietary intakes within the U.S. population or subpopula-
tions in order to estimate the prevalence of inadequate
nutrient intake. It did not examine methods to assess
individual intakes or to determine the adequacy of an
individual diet. In agreement with most analysts of
survey data, the subcommittee determined that to assess
dietary intake at the population level, it is necessary
to compare the observed dietary intakes with the require-
ments for that nutrient.
The subcommittee began by examining previous efforts to
estimate the prevalence of inadequate nutrient intake,
focusing on the scientific merits of the approaches that
have been taken. Recognizing that a probability approach
had been used with apparent success for similar analytic
problems (e.g., analysis of data on height and weight),
the subcommittee tested the feasibility of this approach
for analysis of dietary adequacy. During the course of
its work, it became aware of the importance of three
concepts for this kind of analysis:
· Because food and nutrient intakes vary from day to
day, survey data on dietary intake must be adjusted to
estimate statistically the distribution of usual dietary
intake.
Any approach to the assessment of dietary intake
must take into account the mean and symmetry of the dis-
tribution of nutrient requirements among persons with
similar characteristics. mere is ample evidence that
these nutrient requirements vary between persons in
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similar categories of age, sex, body weight, and pregnancy
and lactation status.
· Because changes in physiological or functional
criteria for nutrient requirements require changes in the
level of dietary intake needed to meet the requirement,
any approach to interpreting intake in relation to require-
ment must incorporate a definition of the criterion the
requirements are intended to satisfy. Tt is possible, and
indeed desirable, to define multiple criteria of adequacy,
multiple levels of requirement, and hence a multitiered
population assessment.
Chapters 3 and 4 of this report address these issues
and are followed in Chapter 5 by a discussion of the
proposed analytic method, including examples of appli-
cations to selected nutrients. The subcommittee also
recognized other important uses for data on food con~ump-
tion, including the identification of food patterns asso-
ciated with inadequate dietary intake and the aetermina-
tion of changes in eating patterns that are likely to be
acceptable, feasible, and economical for groups with poor
diets. This kind of information is needed to design food
assistance programs and meal patterns for these programs,
to encourage improvements in nutrition education, and to
design nutrition intervention programs mandated by law.
Information on food consumption patterns is also essential
for the development of food safety regulations, which are
promulgated by the Food and Drug Administration (FDA) and
the Environmental Protection Agency (EPA). These uses,
although not germane to this report, are as Important as
estimating the prevalence of inadequate intake and are a
major function of the NFCS and other dietary intake sur-
veys. The subcommittee has cautioned that the final design
of future surveys must take into account all the intended
uses of the data--nc~t: just assessment of the prevalence of
inadequate intakes discussed in this report.
Representative terms from entire chapter:
food consumption
