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OCR for page 79
9
Conclusions and Recommendations
In keeping with its mandate, the subcoNmittee's main
suggestion is the adoption of a new approach to the inter
pretation of dietary intake data that are collected in
large surveys such as the Nationwide Food Consumption Sur-
vey (NFCS). The subcommittee has also recommended changes
in the design of these surveys to facilitate or improve the
reliability of interpretations of nutritional adequacy and
to improve the data bases, thereby facilitating application
of the recommended approach. Some of these recommendations
are applicable immediately, even retrospectively, to exist-
ing data from surveys, whereas others could be implemented
in the next NFCS survey. Still others relate to longer
range activities and research programs sponsored by U.S.
Department of Agriculture (USDA) and other agencies.
Although the subcommittee recognizes that recommendations
related to longer term activities will require more time
for implementation, it urges that immediate steps be taken
toward their adoption in view of their importance.
ANALYSIS OF DIETARY ADEQUACY
-
-
The subcommittee concluded that many disadvantages and
erroneous interpretations are associated with the appli-
cation of fixed cutoff points, i.e., the Recommended Dietary
Allowances (RDAs) or percentages of them, as criteria for
the interpretation of observed nutrient intake and that the
use of fixed cutoff points may lead to erroneous estimates
of the prevalence of inadequate intake.
~ The subcommittee recommends that a probability approach
to the interpretation of computed nutrient intake be devel-
oped and adopted, where feasible. This approach would lead
79
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80
to estimates of the prevalence of inadequate intake along
individuals in the total population and in population sub-
groups. This approach is not necessary for nutrients con-
sumed in excess of the RDA by almost all members of the
population, for whom adequacy of nutrient intake can be
assumed.
The subcommittee recognizes that nutritional assessments
based on multiple levels of adequacy are important to govern-
ment agencies and others for use in planning various nutri-
tion programs and in reaching a better understanding of the
nutritional needs of the U.S. population. With a multilevel
approach, for example, one might look at the intake levels
deemed inadequate to prevent clinical manifestations of
deficiency, to maintain the functional integrity of meta-
bolic systems, or to maintain high tissue concentrations of
nutrients if that level is continued for a long period.
Each of these levels is different. Although the subcom-
mittee did not propose a particular set of criteria for this
multilevel approach, it concluded that a multilevel assess-
ment of expected dietary adequacy in the U.S. population
will provide a more useful picture of nutritional adequacy
for planners.
· The subcommittee further recommends the development of
multiple criteria for nutritional adequacy and estimates of
intake required to maintain the various levels of adequacy.
To implement the probability approach, it is necessary to
bring together information about the distribution of nutri
ent requirements among similar persons (e.g., young adult
-
males, young adult females, children of specified ages).
This information about the distribution of nutrient require-
ments is not always presented in directly applicable form in
the Recommended Dietary Allowances (NRC, 1980) or in other
reports' although it might be derived from the studies that
are reviewed in the text of such reports. Sensitivity anal-
yses have shown that estimates of the average requirement
and some idea about the symmetry of the distribution are more
important than a precise estimate of the variability. To
implement the first recommendation given above, such infonma-
tion must be reviewed and judgments must be made about the
distributions.
· The subcommittee recommends that working descriptions
of the distributions of nutrient requirements be developed
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81
and improved. Such descriptions should place major
emphasis on deriving estimates of, or judgments about,
both the central tendency of the distribution and the
symmetry of the distribution. Although precise knowledge
of the characteristics of the distribution is desirable,
it is not essential; estimates of the range can be used.
The probability approach proposed in this report pre-
cludes the classification of individuals as having ade-
quate or inadequate diets. In addition, it would be very
difficult, if not impossible, to estimate the proportion of
populations with multiple dietary inadequacies. For sub-
groups of the population, however, it is possible to esti
mate the prevalence of deficiency for separate nutrients.
Thus the existence of multiple inadequacies in a population
group and possibly in different people can be estimated,
even though this is not possible for individuals.
The subcommittee recommends that multiple dietary
inadequacies be assessed from NFCS data only for popula-
tions and subpopulations--not for individuals.
The probability approach cannot be applied to the inter-
pretation of observed energy intake, even if perfectly mea-
sured, because the intake and requirements are highly cor-
related in well-fed populations such as that of the United
States.
· The subcommittee recommends that the probability
approach not be applied to the interpretation of observed
energy intake. In well-fed populations, energy status as
judged by stores must be assessed by anthropometry. Energy
intake might be viewed as a potential measure of the implied
distribution of physical activity in the total population
and in population subgroups.
The subcommittee concluded that for same nutrients, it
is inappropriate to base inadequate intake estimates on
dietary information. Major environmental variables that
influence requirement (e.g., the importance of sunlight
exposure in the determination of vitamin D requirements)
have not yet been assessed for all nutrients. Moreoever,
information about requirements is often fragmentary (e.g.,
for calcium) and data on current food composition may be
inadequate (e.g., for folate). For these nutrients, it is
nevertheless appropriate to derive descriptive information
about observed intake and to make comparisons among subpopu-
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82
rations, even though the assessment cannot be made as accu-
rately as for the majority of nutrients.
· The subcommittee recommends that prevalence estimates
of inadequate intakes be attempted for nutrients only when
acceptable information about requirements and adequate food
composition data are available.
When no probability assessment can be made for a
nutrient, the subcommittee recommends the descriptive
presentation of the mean, variance, and percentile dis-
tributions.
With the probability approach described in this report,
one can estimate the absolute prevalence of inadequate
dietary intakes, defined as intakes that will not main-
tain appropriate biochemical stores or functions. Many
uses of the NFCS do not require such absolute prevalence
estimates. In particular, differences between population
groups can be determined with other statistically more
powerful methods.
The subcommittee recommends that the probability
approach not be used to generate prevalence estimates for
statistical testing of comparisons between or among subpop-
ulations for which statistically more powerful methods
exist.
In the judgment of the subcommittee, all the above
recommendations can be applied immediately. The proba-
bility approach can be investigated, developed, and imple-
mented with several existing survey data bases.
STUDY DESIGN
The interpretation of the probability approach and its
application to the assessment of observed nutrient intake
involves several important statistical considerations.
These considerations should help to determine the design of
data collection, the methods of analysis, and the inter-
pretation.
A major requirement for the application of the proba-
bility approach, or any other approach used to interpret
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83
the distribution of observed intakes, is the use of statis-
tica1 procedures that take~into account the effect of
day-to-day variation in nutrient intake within the indi-
vidual. The subc`-~.,~ittee addressed this matter and outlined
procedures for implementation. Absolute prerequisites for
these procedures are repeated observations on individual
daily intake. There must be sufficient numbers of replica-
tions for population subgroups as well as for the popula-
tion as a whole. The precise neat - ' of replications needed
should be considered when designing the survey. Moreover,
there appears to be an increase in statistical power if the
replicated 1-day intake estimates are obtained by the same
method and on independent rather than on adjacent days. It
is important also to sample days of the week in the design
and to include questions on dietary supplements as well as
on food intake.
Considering these survey design requirements and the pre-
v~ously identified need for statistical services in connec-
tion with analysis and interpretation, the subcommittee
makes the following recommendations:
m e scope of the statistical services that are inte-
gral to the design, analysis, and interpretation of the NFCS
should be reinforced and expanded.
During the planning of future surveys, the following
aspects of the design should be considered: tl) the number
and distribution of replicate intakes required for statisti-
cally reliable adjustments of the distribution of observed
intakes to estimate the distribution of usual intakes for
the population and subgroups, (2) the wisdom and feasibility
of modifying data collection to include a single method for
use over all days of observation rather than the two systems
presently used to collect dietary information, and (3) the
need and feasibility of sampling on independent rather than
on consecutive days.
Investigations of dietary methodology should con-
t~nue to be presented and published in order to obtain
additional information on such matters as (1) the associa-
tion between intake estimates made on the first days of
observation and those made on subsequent days (correlation
of intake across days) tuna hence the relative importance of
sampling on independent days and (2) sampling, respondent,
or interviewer biases that may affect the reliability of
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84
population intake estimates and hence methodological
approaches that might avoid or minimize any biases that do
exist. The characteristics of respondents likely to have
biases in reported intake data should be identified, and
the direction, and where possible the magnitude, of the
biases should be estimated. Priorities for methodological
research of this kind for the NFCS should include statis-
tical considerations pertinent to the planning of survey
design, data analysis, and data interpretation.
Because the assessment of inadequate (or excessive)
nutrient intake is not the only important use for NFCS data,
the subcommittee concluded that data requirements for other
applications may differ from those identified in the pres-
ent report or implied by the recommendations contained here
in. Thus, it will be necessary to consider all intended
purposes of the survey during the design phase.
· The subcommittee recommends that the USDA review the
important uses of the data to ensure that the survey design
is adequate for an appropriate balance among these uses.
SENSITIVITY ANALYSIS
Although the subcommittee did not arrange the recommen-
dations in any order of priority, the report does show some
of the approaches that might be used to derive a priority
ranking. For example, it is possible to test the effect of
-
incluaing food composition errors in est~mates of the preva-
lence of inadequate intake. (See examples presented in this
report for testing the sensitivity of the prediction to var-
iability of requirement, to errors in estimates of nutrient
intake, and to variability of food composition. ) The rel-
ative effect of various sources of error on estimations of
the prevalence of inadequate or excessive intakes can be
identified. To the extent that these effects of error dif-
f er between nutrients, they can be used to establish pri-
ority ranking for nutrients. In addition to these consid-
erations, the relate ve cost of reducing an identified
source of error should be considered in judgments about
priorities for data improvements.
The following recommendations, then, are not presented
in any order of priority, although these actions should be
implemented to the extent that resources permit.
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85
IMPROVEMENT OF THE FOOD COMPOSITION DATA BASE
The discussions in Chapters 7 and 8 and in Appendices C
and E have illustrated that bias and variation in food com-
position data can have a significant impact on prevalence
estimates. The subcommittee recommends that the USDA
recognize the importance of the food composition data to
the accuracy of the such estimates and that it implement
the recommendations in this chapter. .
The subcommittee recognizes the need to improve the data
base on almost all nutrients in some foods and on some
nutrients in almost all foods. It also recognizes that such
improvements may have limited importance for public policy
purposes either because there is little or no public health
concern about the nutrient and, hence, limited reason to
improve precision of estimates or because the missing or
unreliable data refer to foods that make a minor contri-
bution to intakes and, hence, whose errors have minimal
impact on the estimate of prevalence of inadequate intakes.
The subcommittee has not attempted to judge or assess the
relative priorities for improving the data base. Rather, it
has chosen to recommend areas where improvements could be
made. Before these recommendations are assigned relative
priorities, sensitivity analyses of the type presented in
this report should be conducted to establish whether orient
improvement of the data base would have practical
slgn~rlcance.
The subcommittee was asked to discuss four nutrients for
which there are inadequate methodologies. Of these, fola-
cin, the carotenoids, and vitamin C may be of present or
future public health significance.in the United States.
Existing methodologies are also inadequate for Vitamin B12.
· Thus the subcommittee recommends that the USDA pro-
vide the necessary resources for developing an adequate
methodology for assaying.folacin, the carotenoids, vitamin
B12, and vitamin C in foods if justified by their public
health significance and by sensitivity analysis.
Fox the other nutrients listed in the charge to the
subcommittee for which there are adequate analytical method-
ologies, there are a number of foods for which there either
are no data or only imputed data. For some foods, nutrient
values are determined by adding the individual ingredients
listed in the formulation rather than by direct analysis.
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86
· Given the potential impact of imputed data on the
prevalence estimates, the subcommittee recommends that the
USDA impute values in the food composition data bases so
that no zero values are substituted by default for missing
values.
· The USDA should differentiate between imputed values
and values that are calculated or determined by laboratory
analyses in food composition data bases and clearly iden-
tify calculated and imputed values so that users can readily
differentiate among these values when interpreting the prev-
alence estimates.
The subcommittee believes that priorities for the acqui-
sition of new analytical data should be based on the contri-
bution of the food to the nutrient intake of the population.
Therefore the subcommittee recommends that the USDA
perform sensitivity analyses on the imputed values of all
foods for which data on key nutrients are missing to deter-
mine the probable impact of these foods on the total nutri-
ent intake in the populations of interest.
When the results of the sensitivity analyses are known,
the subcommittee recommends that the USDA perform the fol-
lowing functions:
.
It should collect analytical data for foods contain-
ing nutrients shown by sensitivity analyses to have the
greatest impact on prevalence estimates.
· It should ensure that the foods sampled represent the
total foods consumed in the United States. Where the range
of nutrient composition for a currently classified food is
wide, it should consider subdividing the existing classi-
ficat~on into smaller groups with narrower ranges of com-
position. Such restructuring may be most appropriate for
processed foods as was the case for breakfast cereals in
the current data bases. Again, this decision should be
preceded by sensitivity analysis.
The USDA should also increase the number of assays
for selected nutrients to decrease standard errors of the
mean, where sensitivity analyses indicate that the preci-
sion of the prevalence estimates will be significantly
improved .
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87
The subcommittee believes that the usefulness of the
dietary survey data bases Can be improved. Toward this end,
it recommends the following:
.
The USDA should publish and document the algorithms
and procedures used in the computation of the nutrient
intakes and their variance, the means and the standard
error of the means in food composition data bases, and the
prevalence estimates and their variances.
· The USDA should publish the concentrations of the
individual isomers of the nutrients in food composition
data bases, tables, and dietary intake data tapes.
The subcommittee believes that the bioavailability of
some nutrients may affect prevalence estimates. Thus the
subcommittee recommends the following:
The USDA should promote and support research that
leads to an understanding of the major factors that influ-
ence the bioavailability of key nutrients and the develop-
ment of algorithms for predicting the bioavailability of
these nutrients in meals.
When the understanding and algorithms have been devel-
oped, the agency should use sensitivity analysis to assess
the impact of including bioavailability in the calculation
of prevalence estimates. Further actions should be based
on the outcome of these sensitivity analyses.
The subcommittee believes that public interest in the
maintenance of optimal health will continue and that the
food consumption surveys will be expected to provide more
information on this aspect of diet and public health. Many
of the dietary components believed to enhance or retard the
development of diseases such as cancer and cardiovascular
disease have not traditionally been listed in food composi-
tion tables. Thus it has not been possible to assess
dietary intake of such compounds in the population through
the food consumption surveys. The subcommittee believes
that listing these compounds in the food composition tables
would significantly enhance the ability of the USDA to
respond to anticipated questions on the intake of food com-
ponents by the U.S. public and will provide the U.S. popula-
tion with much better information on the adequacy and safety
of its diet. However, the analysis necessary to acquire
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88
this information could also be very costly. Thus the sub-
c~ittee recommends the following:
· The USDA should investigate the possibility of ex-
panding the food composition data bases to include listings
for all compounds in foods that are believed to affect
human health so that the intake of these components can be
assessed in future surveys.
· Where potential health benefit is likely, and the
quality of the chemical analysis warrants, the USDA should
analyze these components, many of which are not nutrients,
and include them in the food composition data bases.
PREREQUISITES AND LIMITATIONS OF THE PROPOSED APPROACH
.
The subcommittee is aware that its report poses a number
of questions regarding the immediate application of the pro-
posed approach to the analysis of nutrient intake data. As
indicated by the report of one member (see pp. 104-109),
there was not complete agreement about the practicality of
the approach. All members of the subcommittee are in agree-
ment on the scientific validity of the proposed approach
and on the nature of these unresolved issues relating to
survey design and data base adequacy; however, opinion
varied as to the probability of success in developing the
Information needed to apply the approach and the time that
will be needed for the required research. The subcom-
mittee's judgments are presented under four major areas:
acceptable precision of estimates of the prevalence of
inadequate intake, estimation of usual food intake, compu-
tation of nutrient intake, and definition of nutrient
requirements.
Acceptable Precision of the Estimates
Consideration of the use of estimates of the prevalence
of inadequate intakes and of the overall implication of the
proposed approach led the subcommittee to discuss the ac-
ceptable level of accuracy for prevalence estimates. In
Chapter 8, estimates of the confidence intervals for esti-
mates of the prevalence of inadequate intake are presented.
These take into account all recognized potential sources of
bias in the prevalence estimate with the exception of
systematic bias in reporting intake or misestimation of
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89
mean requirement. In the considered judgment of members of
the subcommittee, errors even severalfold greater than
those estimated in Chapter 8 would be acceptable for policy
analyses. On this all members of the subcommittee agreed.
The areas of differing opinion within the subcommittee
concerned ideas about the magnitude of unmeasured errors.
Estimation of Usual Food Intake
The omission of homeless and institutionalized persons
from the sampling frame for the NFCS has already been
mentioned in Chapter 7. This omission will lead to sys-
tematic underrepresentation of the population at highest
risk of nutritional deficits, thereby biasing the results
of the study to some extent. The subcommittee has recom-
mended further research to estimate the magnitude of this
bias and to reduce it. This appears to be amenable to sat-
isfactory resolution Through applied research and appro-
priate survey design, including collaboration with other
national surveys. Even though NFCS may continue to under-
sample or omit certain segments of the population, it may
be possible to gain information about these segments from
other surveys, thus complementing NFCS information without
necessitating a radical change in the NFCS design. Any
residual limitations of the design, and hence the need to
draw upon other information, should be made clear to users.
The subcommittee recognizes that subj eats may vary in
the reliability with which they report food ingested.
There may be random under- and overreporting by one sub-
ject across days.
A subject may consistently under- or
overreport, but this may be random between subjects. Or,
the entire group may systematically under- or overreport.
The nature and extent of these effects in the NFCS are not
known. In Chapter 7, the subcommittee considered the
potential impact of variations in reporting and concluded
that random variation in the reports of one subject would
have no Impact on the prevalence estimate derived by the
proposed method. Random variation between subjects would
have an effect on the estimate. Within the plausible range
of magnitude of these effects, however, the bias introduced
in the prevalence estimate would be acceptable for policy
applications of the results. The subcommittee concluded
that a serious potential effect would derive from any
appreciable systematic under- or overreporting across the
entire population or subpopulation under study. In the
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so
absence of specific information about the magnitude of this
phenomenon, if it exists in the NFCS, opinions about reli-
ability of the prevalence estimates varied For those
mothers who believed the problem to be large, there were
also differences of opinion about the feasibility of
improving the collection of data on dietary intake and
analytical procedures to minimize the impact on the prev-
alence estimates. There was unanimous agreement that the
USDA should continue its efforts to assess the magnitude of
reporting bias. If bias is found, the USDA should increase
its efforts to Improve methods for collecting data on
reduction of bias in dietary intake data and analytical
methods to correct for known bias in derivations of the
prevalence estimate.
The subcommittee emphasizes that where other information
documents 'he existence of ~ nutritional problem in the
population, meaningful comparison of intakes between popu-
lation groups can be made without use of the probability
approach.
Computation of Nutrient Intake
As was discussed in Chapter 7, error can also enter into
the estimates during the conversion of food intake data into
nutrient composition data. This process is dependent on the
sampling of foods for chemical analysis, the analytical
methods used, the coding categories used to describe foods
in the food composition data set, and the computation of
nutrient intake. The greatest potential for error in this
process is associated with the analytical methods selected
and the representativeness with which foods are sampled.
The subcommittee believes that the analytical methods for
vitamin C and folate and for the vitamin A carotenoids may
produce inaccurate data and that sensitivity analysis is
required to determine the extent of this effect on the
probable outcome of improved assays for these nutrients.
The results of these sensitivity analyses should indicate
whether it would be worthwhile to develop better analytical
methods to correct errors in the existing data. Improve-
ments of this kind are feasible.
Error may also be introduced into the estimates during
the computation of nutrient intake. The subcommittee con-
cluded that imputed values may be a source of such error
and calls for identification of imputed values in the data
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91
sets on nutrient composition. The significance of the
impact of imputed values should also be determined through
sensitivity analysis. Selective assaying of foods shown by
the sensitivity analysis to be responsible for errors in
the final data could then be undertaken. Again the sub-
committee believes that action can be taken to manage this
issue.
Members of the subcommittee agreed that variations in
the bioavailability of nutrients will produce errors in
estimations of the nutrient intake of a person. However,
across individuals, the effect may be no more important
than the random under- and overreporting across individ-
uals, as considered earlier. Opinions varied as to the
present importance of the problem and the potential for
its solution. Nutrients for which errors are likely to
have the greatest impact are iron, zinc, and folate.
The subcommittee unanimously agreed that errors in the
computer algorithm for computations of any nutrients, to
the extent that they exist, would have an impact on the
estimates and that these can and should be corrected.
Definition of Nutrient Requirements
As was discussed in detail in Chapter 3, information on
the mean and approximate symmetry of the nutrient requlre-
ment is needed in order to apply the probability approach.
Analyses performed by the subcommittee and presented in
Chapter 5 show that differences in the standard deviation
and range of the distribution have a minimal effect on the
estimates as long as the distribution is symmetrical.
Therefore, imprecision in the description of the variance
of requirement was not a major issue. Lack of information
on mean nutrient requirement was a major concern for all
members of the subcommittee; however, views on the pre-
cision of the requisite estimates of mean nutrient require-
ment varied. Some members believed that reasonable esti-
mates of mean requirement can be constructed immediately
for many nutrients across requisite age and sex groups and
that these estimates will provide a rational basis for
analysis. Others believe that more definitive and scien-
tifically validated estimates are required. In the face of
these differing opinions on the level of specificity and
criteria of proof needed for mean requirement data, there
was a lack of agreement on the likelihood of developing
this information in the foreseeable future.
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92
There was agreement in recommending that multiple levels
of requirement, reflecting a series of states of nutriture,
be developed and applied. These might relate, for example,
to the prevention of scurvy on the one hand and to the main-
tenance of tissue stores of ascorbic acid on the other.
There was recognition that ascorbic acid may have other
effects, perhaps unrelated to its nutrient properties, such
as anticarcinogenicity. Requirements to achieve this effect
are not known. Other nutrients may require similar cons~d-
erations. All members agreed that widespread chronic dis-
eases in the United States require more attention than defi-
ciency diseases, which are rare in the general population.
One member was not certain whether the probability approach
could be used for chronic diseases. All other members
believe it is important to pay continuing attention to the
potential for dietary deficiency in the U.S. population.
CONCLUSIONS
The subcommittee has stressed the many important uses of
NFCS data. In addition to estimating the prevalence of in-
adequate intakes, the data permit examination of food use
and of dietary patterns. For example, the data are used to
establish the patterns of food use associated with nutri-
tional deficiency and with undesirably high levels of nutri
ent intake (e.g., fat intake). Information about food use,
as distinct from nutrient intake, is essential in setting
attainable nutritional standards for food assistance
programs, for designing meal patterns to meet these pro-
grams, and for designing and implementing nutrition educa-
tion and other nutrition intervention programs intended to
ameliorate nutritional problems detected by whatever means
in the U.S. population or groups at particular risk. Infor-
mation about food consumption is essential also in the
development of food safety regulations. Thus the NFCS data
base is important in supporting many national activities
mandated by law. There is no clear replacement, now or in
the future, for NFCS data for these types of users.
In recommending design and interpretational enhance-
ments for assessing the prevalence of inadequate intakes,
the subcommittee recognizes that this is but one use of the
NFCS and not necessarily the most vital use. Therefore, it
has repeatedly cautioned that all uses of the data should
be considered in making final survey design decisions.
-
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93
The subcommittee was specifically required by its mandate
to evaluate methods to assess observed dietary intake. All
except one mother of the subcommittee believed that for sev-
eral nutrients, it should be possible to apply the proba-
bility approach, as recommended, at this time.
All the above limitations to the immediate application
of the probability approach apply just as much to any other
analytical method that is based on a comparison of intakes
to requirements (e.g., use of RDA-based cutoffs, nutrient
density). Furthermore, to be applied properly, these other
methods would also require even more information than the
probability approach and this information may be even more
difficult to obtain. For this reason, the probability
approach has been identified as the preferred method.
After examining the use of fixed cutoff points to analyze
dietary adequacy, the subcommittee concluded that attempts
to estimate absolute prevalence of inadequate intake using
the RDAs or any fixed proportion thereof have no scientific
validity and that the results of this type of analysis can-
not be meaningfully interpreted. The one exception to this
conclusion is analysis for nutrients for which the entire
or almost the entire distribution of usual intake is above
the RDA. In such cases, it is possible to conclude that
inadequate intake is not a major public health problem for
that particular nutrient and category of age and sex.
All the recommendations of the subcommittee can be
implemented immediately or as a part of a phased approach
to implementation. The interpretational approach does not
mandate major changes in survey design and therefore should
not delay the survey itself. However, the interpretation
of the data requires development of the average requirement
estimates needed to implement the probability approach.
This is beyond the mandate of the subcommittee and could be
a task for the National Research Council's Committee on
Dietary Allowances. Some preparatory work can be initiated
immediately by the USDA. Sensitivity analyses to determine
which error sources have a meaningful impact on estimates of
prevalence of inadequate intakes, as exemplified within the
present report, are recommended for continuation through the
next few years. These would serve to resolve disagreements
of opinion about the Importance of different potential
sources of error. More focused sensitivity analyses for
nutrients with a potential for having an important impact
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94
will guide the longer term research efforts needed for a
full application of the approach.
Appropriately analyzed, dietary data can be used as a
basis ,-or judging the presumed adequacy of intake. The
subcommittee has proposed an appropriate approach to such
interpretation. This application is distinct from an
assessment of the state of health consequent to inadequate
intake. As discussed in a previous report (NRC, 1984),
biochemical and clinical observations included in other
national surveys are more appropriate for the assessment of
nutritional status per se. Nevertheless , dietary data,
such as those collected in NFCS, are required in inferring
a dietary causation of observed health effects and in
considering dietary actions that might ameliorate them.
Representative terms from entire chapter:
food composition
