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OCR for page 19
I t d t. t
· ~
Dletary P. annlng
This report is one of a series of publications resulting from a
comprehensive effort initiated by the Institute of Meclicine's Food
and Nutrition Board in 1993 to expand the approach to the clevel-
opment of clietary reference stanciarcis. The new categories of refer-
ence values have specific uses and thus are a significant departure
from the previous Recommencleci Dietary Allowances (RDAs) in
the United States and Recommencleci Nutrient Intakes (RNIs) in
Canada. The focus of this report is to examine the appropriate use
of each of the available types of Dietary Reference Intake (DRI)
values in planning nutrient intakes of groups and inclivicluals.
This report should be of particular use to nutrition and public health
researchers in their work, to dietitians and nutritionists responsible
for the education of the next generation of practitioners, and to the
government professionals involved in the development and imple-
mentation of national cliet and health assessments, public ecluca-
tion efforts, and food assistance programs. The report reviews the
statistical underpinnings for the application of the various types of
DRI values in planning, illustrates sample applications, and provides
guidelines to help professionals determine when specific uses are
anoronriate or inanoronriate.
Planners neeci to have a good unclerstancling of the DRIB, incluci-
ing how each requirement was cleriveci, and whether the Tolerable
Upper Intake Levels were baseci on all sources of nutrients or just
fortificants and supplements. An unclerstancling of basic statistics is
also needed, especially for group planners. Planners must under-
stanci the concepts of risk and probability.
19
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20
DIETARY REFERENCE INTAKES
BACKGROUND
The term Dietary Reference Intakes (DRIB) refers to a set of nutrient-
baseci reference values, each of which has special uses. The clevelop-
ment of DRIs expands on the periodic reports called Recommended
Dietary Allowances (RDAs), which have been published since 1941 by
the U.S. National Academies, and the Canaclian Dietary Stanciarcis,
called Recommended Nutrient Intakes (RNIs) published since 1938 by
the Canaclian government. This comprehensive effort has been uncler-
taken by the Stancling Committee on the Scientific Evaluation of
Dietary Reference Intakes of the Food and Nutrition Board, Insti-
tute of Medicine, National Academies, at the request of the U.S.
government and Health Canada.
A previous report in this series (IOM, 2000a) examined the use of
DRIs in clietary assessment for inclivicluals and groups. Dietary assess-
ment, whether for an incliviclual or a group, compares usual nutrient
intakes with estimated nutrient requirements and examines the
probability of inacloquate or excessive intake. Dietary planning, on
the other hanci, aims for the consumption of cliets that have accept-
ably low probabilities of inacloquate or excessive nutrient intakes.
Dietary planning involves using the DRls to set goals for what intakes
should be.
Dietary planning may be done at several different levels. It may refer to an
individual planning a meal and making relevant food purchases, a food
service manager in an institution planning daily menus, or a government
agency planning large nutrition or food assistance programs. For the pur-
poses of this report, dietary planning applies to planning intake, rather than
the amount offood purchased or served.
Nutritional considerations are only one component of clietary
planning. Other considerations include incorporating food prefer-
ences of the incliviclual or group being planned for, and the cost
and availability of foocis. However, using estimates of nutrient
requirements to set intake goals should be part of the planning
activity.
Figure 1-1 illustrates a conceptual framework clescribecT by Beaton
(1994) that can be applied to the interpretation and uses of the
DRIB. As shown in the framework, knowledge about both nutrient
requirements and nutrient intakes feecis into two general applica-
tions: cliet planning and cliet assessment. Within each of these gen-
eral categories, the applications differ according to whether they
are for an incliviclual or for population groups.
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INTRODUCTION TO DIETARY PLANNING
| Nutrient l
| Requirements l
l
Nutrient Intakes
(food plus supplements)
1
:~ Assessing
~~ L Diets |
/.
Group | | Individual | | Group I | Individual
FIGURE 1-1 Conceptual framework uses of dietary reference standards.
SOURCE: Adapted from Beaton ( 1994~ .
21
The simplicity of the above statements belies the complexity in
using and interpreting DRIs to plan and assess diets. Two important
factors account for this complexity. In the past, both planning and
assessment applications have reliecT primarily on the former RDAs
and RNIs because these were the only nutrient stanciarcis wiclely
available. Often, the concepts underlying the former RDAs and
RNIs were not well unclerstoocT, and thus some applications for both
assessment and planning purposes were inappropriate (IOM, 1994~.
Therefore, aciclitional types of reference intakes have been clevelopecT
(Estimated Average Requirement, Acloquate Intake, and Tolerable
Upper Intake Level). With the three additional categories of dietary
reference intakes now available, applications need to be carefully
consiclerecT and clearly explained so each of the categories are used
appropriately. DRIs can be used in situations such as planning incli-
viclual cliets; planning nutrition and food procurement for the mili-
tary, prisons, nursing homes, and other institutionalized groups;
food labeling and nutritional marketing; clinical dietetics; food for-
tification; developing new or modified food products; and assessing
food safety.
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22
DIETARY REFERENCE INTAKES
The approaches cliscusseci in this report for using the DRIs as a
guide in planning clietary intakes for inclivicluals and for groups rely
on the same basic principles that were presented in the previous
report on applications of the DRIs in clietary assessment (IOM,
2000a). Those principles provide the rationale for using each of the
DRIs for incliviclual and group cliet assessment, and the same ratio-
nale extends to the use of the DRIs in cliet planning.
WHAT ARE DIETARY REFERENCE INTAKES?
As inclicateci above, the term Dietary Reference Intakes (DRIB) refers
to a set of at least four nutrient-baseci reference values that can be
used for planning and assessing cliets and for many other purposes.
An important principle underlying both the former Recommencleci
Dietary Allowances (RDAs) and Recommencleci Nutrition Intakes
(RNIs) and the new DRIs is that these are standards for healthy people
they are not appropriate for individuals or groups who are ill orfor repletion
of deficient individuals.
The concepts underlying the new DRIs differ from the former
RDAs and RNIs as inclicateci in Box 1-1.
Processes Used to Establish the Dietary Reference Intakes
In establishing the EAR or Acloquate Intake (AI) for nutrients, a
requirement is clefineci as the lowest continuing intake level of a
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INTRODUCTION TO DIETARY PLANNING
23
nutrient that will maintain a clefineci level of nutriture in an inclivici-
ual. The chosen criterion of nutritional acloquacy upon which this
requirement is baseci is different for each nutrient and is iclentifieci
in the DRI nutrient reports (IOM, 1997, 1998a, 2000b, 2001,2002a).
In some cases, the criteria may differ for inclivicluals at different life
stages for the same nutrient. In developing the DRIB, emphasis is
placed on the reasons underlying the particular criterion of acle-
quacy used to establish the requirement for each nutrient. A more
cletaileci discussion of the origin and framework of the DRIs is pre-
sented in Appendix A.
The EARs are baseci on a thorough review of the scientific litera-
ture for health outcomes associated with the nutrient. The criteria
and eviclence-baseci rationale used for setting each EAR are clearly
specified. An estimate of the variation in the requirement is also
specified, and is used to set the RDA. When ciata are inacloquate to
establish an EAR and RDA, other approaches are used to establish
an intake goal, which is clesignateci an AI. The process used to estab-
lish the UL involves the estimation of an uncertainty factor that is
applied to a no-observeci-aciverse-effect level (NOAEL) or to a
lowest-observeci-aciverse-effect level (LOAEL) baseci on human or
animal ciata related to iclentifieci hazards.
· . · . · .
Estimated Average Requirement1
The Estimated Average Requirement (EAR) is the usual intake level
that is estimated to meet the requirement of half the healthy incli-
vicluals in a life stage and gentler group. At this level of intake, the
other half of the healthy inclivicluals in the specified group would
not have their neecis met. The EAR is baseci on a specific criterion
of acloquacy, cleriveci from a careful review of the literature. When
selecting the criterion, reduction of disease risk is consiclereci along
with many other health parameters. For example, the EAR for
vitamin C is baseci on "an amount thought to provide antioxidant
protection as derived from the correlation of such protection with
neutrophil ascorbate concentrations" (IOM, 2000b). For energy,
1 It is recognized that the definition of EAR implies a median as opposed to a
mean or average. The median and average would be the same if the distribution of
requirements followed a symmetric distribution, and would diverge as the distribu-
tion became skewed. Two considerations prompted the choice of the term EAR:
(1) data are rarely adequate to determine the distribution of requirements, and
(2) precedent has been set by other countries that have used the term EAR for
reference values similarly derived (COMA, 1991~.
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24
DIETARY REFERENCE INTAKES
the situation is somewhat different. Energy requirements are esti-
mateci on an incliviclual basis using a person's gentler, age, height,
weight, and physical activity level to estimate total energy expencli-
ture; thus the specific criterion of acloquacy is maintenance of a
healthy body mass inclex with a healthy level of physical activity.
Recommended Dietary Allowance
The Recommended Dietary Allowance (RDA) is the clietary intake level
that is sufficient to meet the nutrient requirement of nearly all
healthy inclivicluals in a particular life stage and gentler group. If
the distribution of requirements in the group is assumed to be
normal, the RDA is computed from the EAR by Hilling two stanciarci
deviations of the requirement (8DREQ) as follows:
RDA = EAR + 2 SDREQ
The stanciarci deviation of the requirement distribution can be
observed directly if sufficient ciata are available. Often this is not the
case, and the stanciarci deviation is estimated by assuming a specific
coefficient of variation (CV) for the average requirement. A CV of
10 percent has been used for many nutrients (IOM, 1997, 1998a,
2000b, 2001), and for these, the RDA equals 120 percent of the
EAR. Therefore, assuming a normal distribution, 97 to 98 percent
of the individuals in the group will have a requirement that is below
the RDA. If the distribution of requirements is known to be skewoci
rather than normal (for example, iron requirements of menstruat-
ing women), the RDA is obtained by fincling the usual intake level
that is at the 97th to 98th percentile of the requirement clistribu-
tion. In either case, the RDA developed in the DRI process differs
conceptually from the former RDAs and RNIs since with the estab-
lishment of an EAR, the RDA is cletermineci quantitatively rather
than through the use of judgment-based safety factors.
The RDA is intencleci for use primarily as a goal for intake of
inclivicluals. Because the RDA is often cleriveci directly from the EAR
and an estimate of variability of the requirement distribution, if
ciata are insufficient to establish an EAR, no RDA can be set.
Adequate Intake
If sufficient scientific evidence is not available to establish an EAR,
and thus determine an RDA, a reference intake called an Adequate
Intake (Al) may be cleriveci instead. The AI is a value baseci on
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INTRODUCTION TO DIETARY PLANNING
25
experimentally derived levels of intake or the mean nutrient intake
by a group (or groups) of apparently healthy people who are main-
taining a defined nutritional state or criterion of adequacy. Exam-
ples of defined nutritional states include normal growth, mainte-
nance of normal circulating nutrient values or biochemical indices,
or other characteristics of nutritional well-being or general health
related to the nutrient.
For example. the AI for voting infants is based on the daily mean
. , ~ ,
· · . . ~ . . . · . . ~ . . . ~ . .
nutrient In take supplied by human milk tor healthy, tull-term
infants who are exclusively breasted. For adults, the AI may be
based on data from a single experiment (e.g., the AI for choline
tIOM, 1998a]), on estimated dietary intakes in apparently healthy
population groups (e.g., the AI for pantothenic acid tIOM, 1998a] ),
or on combined data from different approaches (e.g., usual dietary
intake and experimentally altered intakes of calcium in adult
women tIOM, 19974~. The AI is thus expected to exceed the true
EAR (and often the RDA) if it could be set for the same specified
criterion of nutritional adequacy. In the absence of an EAR (and
RDA) for a nutrient, the AI can be used as the intake goal.
The issuance of an AI is an indication that more research is needed
to determine with confidence the mean and distribution of require-
ments for a specific nutrient. As this research is completed, it should
be possible to replace estimates of AIs with EARs and RDAs.
To;terab;te Upper Intake [event
The Tolerable Upper Intake Level (UL) is the highest level of con-
tinuing daily nutrient intake that is likely to pose no risk of adverse
health effects to almost all individuals in a specified life stage and
gender group. As intake increases above the UL, the potential risk
of adverse health effects increases. The term tolerable intake was
chosen to avoid implying a possible beneficial effect from levels of
intakes above the RDA. Instead, the term is intended to connote a
level of intake that can, with high probability, be tolerated biologi-
cally. The UL is not a recommended level of intake, and there is no
currently established benefit to healthy individuals associated with
ingestion of nutrients in amounts exceeding the RDA or AI.
The UL is baseci on an evaluation conclucteci using the methoclol-
ogy for risk assessment of the adverse effects of nutrients (IOM,
1999~. (A cletaileci explanation of this methodology is also inclucleci
in all of the DRI nutrient reports.) The neeci to establish ULs grew
in part out of the increased fortification of foocis with nutrients and
the increased use of dietary supplements. Details are given for each
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26
DIETARY REFERENCE INTAKES
nutrient on how the UL was established (IOM, 1997, 1998a, 2000b,
2001, 2002a). For some nutrients there may be insufficient ciata on
which to develop a UL. The lack of a UL cannot be interpreted as
meaning that high intake poses no risk of adverse effects.
Unless otherwise stated in the DRI nutrient reports, values given
for EARs, RDAs, AIs, and ULs are baseci on the total intake of the
nutrient naturally occurring in food, acicleci to food as a fortificant,
and from supplements.
IMPLEMENTATION OF DIETARY PLANNING FOR
INDIVIDUALS AND GROUPS
Planning cliets refers to determining what usual nutrient intake
should be. Regardless of whether one is planning cliets for inclivicluals
or groups, the goal is to have cliets that are nutritionally acloquate,
or conversely, to ensure that the probability of nutrient inacloquacy
or excess is acceptably low. As will be clescribeci in depth in this
report, how this goal is implemented differs when planning for
inclivicluals compared to planning for groups. Nevertheless, the
underlying considerations are similar.
At the incliviclual level, usual intake is clefineci as the incliviclual's
average intake over a long period of time. As cliscusseci in greater
detail in the Dietary Reference Intake (DRI) report on clietary assess-
ment (IOM, 2000a), because of the large ciay-to-ciay variation in
incliviclual intake, intake on one or even several clays may provide
inaccurate estimates of an incliviclual's usual intake. Similarly, for
groups, the focus for cliet planning is the distribution of usual intake,
which is the distribution of the long-term average intakes of incli-
viduals in the group. Usual intake distributions can be estimated by
adjusting the observed intake distributions using statistical tech-
niques (NRC, 1986; Nusser et al., 1996) . By removing the ciay-to-ciay
variation in intakes (within-person variation), the resulting adjusted
distribution better reflects the incliviclual-to-incliviclual variation of
intakes within the group.
Another consideration in the implementation of clietary planning
is the concept of an acceptably low probability of nutrient inacle-
quacy (probability that intake does not meet requirement) or, con-
versely, a high probability of nutrient acloquacy. For inclivicluals, an
acceptably low probability of nutrient inacloquacy has been tracli-
tionally accomplished by planning for the incliviclual's usual intake
to be at the Recommencleci Dietary Allowance for the nutrient, such
that the probability of inacloquacy floes not exceed 2 to 3 percent.
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INTRODUCTION TO DIETARY PLANNING
27
To ciate, planning for groups has generally not incorporated plan-
ning for a low prevalence of nutrient inacloquacy, in large part
because the tools required Knowledge of the Estimated Average
Requirement and the usual intake distributions have not been wicle-
ly available. Thus, there is no convention about what prevalence of
inacloquacy is acceptably low. It is in the professional judgment of
the nutritionist or planner to determine what is an acceptably low
probability of nutrient inacloquacy for an incliviclual or prevalence
of inacloquacy for groups. The level selected should be clearly stated.
Similarly, in applying the DRIs for planning, professional judgment
is required to determine the likelihood of any recognized benefit of
increasing intakes beyond their current level.
CAVEATS REGARDING THE USE OF DIETARY REFERENCE
INTAKES IN DIETARY PLANNING AND ASSESSMENT
Dietary planning and assessment are inextricably linked. Assess-
ment is used as a basis for planning and to evaluate whether the
planning goals have been met. Those assessing and planning cliets
should be aware of limitations in the ciata that underpin the Dietary
Reference Intakes (DRIB) and their application: there is uncertainty
associated with the estimates of the Estimated Average Require-
ments (EARs) themselves, and clietary intake and food composition
ciata are subject to inaccuracy.
[imitations in the Data on Nutrient Requirements
Detailed consideration of the DRI reports for specific nutrients
(IOM, 1997, 1998a, 2000b, 2001, 2002a) can provide insight into
both what is known and what information is still needed to further
define intakes that support health. In interpreting the DRIs for use
in dietary planning, planners should be aware that often the EARs
are baseci on ciata from a limited number of inclivicluals; that for
most nutrients the precise variation in requirements is not known
and has been approximated from the variation in related physiological
parameters; that, in the absence of evidence to the contrary, the
variation in individual requirements has been assumed to follow a
normal distribution; that the EAR has often been extrapolated from
one population group to others that differ in life stage and gentler;
and that the degree of uncertainty associated with the EAR has not
been specified. By definition, EARs are estimates they are not
clefineci with 100 percent accuracy. Thus, although the best avail-
able evidence was used, gaps in the knowledge base remain.
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28
DIETARY REFERENCE INTAKES
Choice of Requirement Criterion
Knowledge of the criterion used by the DRI panels to determine
the EAR and Recommencleci Dietary Allowance (RDA) can help in
assessing the potential impact of not meeting these guidelines. This
may affect setting goals for nutrient intake, including selection of
an acceptable group prevalence of clietary inacloquacy (e.g., the pro-
portion of a group with intakes below the EAR).
In establishing the DRIB, the requirements for most nutrients have
been presented as a single endpoint for various life stage and gentler
groups, rather than as multiple endpoints. To the extent that for
most nutrients a single endpoint has been established for an EAR
and RDA, this approach differs from that originally recommencleci
by NRC (1986) and adopted by the Joint Food and Agriculture
Organization and World Health Organization Expert Consultation
on the requirements of vitamin A, iron, folate, and BE (FAD/WHO.
1988~. These groups recommencleci both a basal requirement level
(the amount of nutrient neecleci to prevent a clinically detectable
impairment of function) and a normative storage requirement level
(the amount of nutrient neecleci to maintain a desirable level in
tissues). However, the DRI process floes allow for multiple enci-
points to be used where the ciata exist, and to ciate this has been
clone for vitamin A. An EAR has been set for the reversal of night
blindness, and an EAR and RDA have also been set for the mainte-
nance of liver stores. A planner might want to ensure that intakes
would result in a minimal (near zero) prevalence of inacloquacy
with regard to night blindness, but might be willing to accept, and
thus plan for, a somewhat higher prevalence of inadequacy with
regard to maintenance of normal liver stores.
Inadequate Dietary Intake Versus Inadequate Nutritional Status
Planning cliets for groups involves choosing an acceptable group
prevalence of clietary inacloquacy (see Chapter 3~. Theoretically,
this would correspond to the prevalence of inacloquate nutritional
status with regard to the criterion used to establish the EAR. For
example, if planners chose to maintain the current distribution of
vitamin B6 intake in the United States in women age ci 31 to 50 (see
appendixes to the DRI publications for tables describing the popu-
lation distributions of nutrient intakes tIOM 1997, 1998a, 2000b,
2001, 20021), they would be accepting an apparent group preva-
lence of dietary inadequacy between 10 and 15 percent, according
to ciata from the Third National Health and Nutrition Examination
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INTRODUCTION TO DIETARY PLANNING
29
Survey (NHANES III). If the assumptions involved in establishing
the EAR were correct and applied to all population groups, one
would expect to observe similar proportions consuming vitamin B6
below the EAR and with low plasma pyricloxal phosphate levels (i.e.,
inacloquate nutritional status with regard to the indicator used to
set the EAR). In practice, however, the apparent prevalence of
dietary inadequacy of a nutrient may not be equivalent to the preva-
lence of inadequate nutritional status for the same nutrient.
Sources of error contributing to any observed discrepancies
between estimates of the prevalence of inacloquate intake and inaci-
equate nutritional status include those involved in estimating clietary
intakes. These have been reviewoci in the DRI report on clietary
assessment (IOM, 2000a), and include an incomplete knowledge of
(1) the nutrient composition offoocis, (2) thenutrientbioavailabil-
ity from different food and supplemental sources, (3) the usual
intakes as compared with short-term intakes, and (4) the uncler-
reporting of self-reporteci clietary intakes. The uncertainties involved
in estimating nutrient requirements can also contribute to observed
discrepancies, as can the lack of population data on the biochemical
indicators of nutrient acloquacy used to establish the requirement
estimates.
Sources of Error in Planning for Dietary Intake
Uncertainty of Requirement Estimates
For some nutrients, the sources of error in estimating intakes and
requirements are not extreme, and the apparent prevalence of
clietary inacloquacy (e.g., the proportion below the EAR) corre-
sponcis reasonably well to the prevalence of inacloquate nutritional
status with regard to the criterion used to establish the EAR. For
example, the EAR for iron was established as the amount of iron
needed to meet body functions with minimal storage, and this was
cletermineci to be reflected by a serum ferritin concentration of
about 15 ,ug/L (IOM, 2001~. When the prevalence of inacloquate
iron intakes was compared to the prevalence of apparent biochemi-
cal deficiency (low serum ferritin concentrations), the agreement
was reasonable for most life stage and gentler groups (IOM, 2001~.
If planners chose to reduce the prevalence of dietary inadequacy
(anci, by inference, the prevalence of inacloquate nutritional sta-
tus), this could be clone using the methods clescribeci in Chapter 3
of this report.
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30
DIETARY REFERENCE INTAKES
In other cases, however, errors in estimating clietary intake make
it difficult to use clietary intake ciata to plan cliets with acceptable
levels of inacloquacy. This is especially true for vitamin E. Food com-
position ciata neeci to be upciateci for this nutrient, and clietary
intakes are frequently unclerestimateci clue to underreporting
(which may be particularly problematic for fat, a major carrier of
vitamin E) (Mertz et al., 1991~. Data from NHANES III suggest that
the majority of adults age ci 31 to 50 haci apparently inacloquate
clietary intakes (IOM, 2000b), leaving the impression that cliets must
be planned with aciclitional vitamin E to meet the requirements for
the population. However, examination of the serum oc-tocopherol
distributions in NHANES III reveals that fewer than ~ percent haci
plasma concentrations below the 12 ,umol/L (516 ,ug/ciL) used to
set the EAR. Thus, for vitamin E, it is clear that the apparent preva-
lence of clietary inacloquacy floes not correspond to the prevalence
of inacloquate nutritional status as assessed biochemically. Thus,
when choosing a planning goal, especially when planning for
groups, planners neeci to consider the limitations of the clietary
intake ciata, the consequences of not meeting the criterion used to
determine the EAR, the results of available biochemical ciata, and
the goals of clietary planning for specific situations.
As inclicateci earlier, a nutrient will usually have a Tolerable Upper
Intake Level and either an EAR and RDA or an Acloquate Intake
(AI). However, for energy and the macronutrients, this is not always
the case. For example, no DRIs have been set for total fat for incli-
vicluals over 1 year of age. Instead, an Acceptable Macronutrient
Distribution Range of 20 to 35 percent of energy from dietary fat is
recommencleci for adults to minimize risk of adverse health out-
comes. For energy, no DRIs have been set an estimate of the total
energy expenditure associated with an individual's gender, age,
height, weight, and physical activity level is used.
Uncertainty of Dietary Intake Estimates
Another source of error that has potentially profound implica-
tions for dietary assessment and planning is the accuracy of self-
reported dietary intakes. A variety of study designs has been employed
to examine the accuracy of clietary assessment techniques to measure
individuals' true energy intakes over defined time periods. The
weight of evidence from this extensive literature indicates that a
sizeable proportion of inclivicluals systematically misreport their
intakes, with the tendency toward underreporting. In a now classic
study by Mertz and colleagues (1991), the usual energy intake of
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INTRODUCTION TO DIETARY PLANNING
31
266 adults (estimated from 7 to 35 days worth of food records) was
determined to be insufficient to maintain body weight in 81 per-
cent of subjects. The average discrepancy between self-reported en-
er~v intake and the intake required for weight maintenance was
Jo 1 ~
17 ~ ~ 1 1 ~ ,r , 1 1 rim 1 · , · , 1 1
/()() kcal. More recently, seli-reports ot dietary In take have been
compared to energy expenditure measured by doubly labeled wa-
ter, on the assumption that energy expenditure is equivalent to
intake in situations of energy balance. Such comparisons have typi-
cally revealed substantial underreporting of intakes, even when
changes in body stores during the study period are taken into ac-
count (Bandini et al., 1990; Black et al., 1993; Johnson et al., 1998;
Kaczkowski et al., 2000; Martin et al., 1996; Prentice et al., 1986;
Tomoyasu et al., 1999~. Furthermore, although the nature and
sources of measurement error are known to vary across dietary as-
sessment methods, the problem of underreporting appears to be
pervasive irrespective of whether food records, dietary recalls, diet
histories, or food frequency questionnaires are used to assess intake
(Black et al., 1991; Sawaya et al., 1996~.
Self-reports of dietary intake have also been compared to esti-
mates of energy expenditure based on factorial methods, although
at the individual level, this method yields a less precise estimate of
energy expenditure than the doubly labeled water technique. Typi-
cally, reported energy intake (EI) is expressed as a ratio of estimated
basal metabolic rate (BMReS~), based on age, sex, self-reported or
measured body weight, and possibly height. A variety of approaches
to evaluating the adequacy of EI/BMReS~ can be found in the litera-
ture. Goldberg and colleagues (1991) have proposed a method to
estimate a minimum plausible EI/BMReS~ by applying a series of
assumptions that take into account within-person variation in energy
intake, random error in the estimation of an individual's basal meta-
bolic rate based on the predictive equation used, and variation in
an individual's physical activity level. When these methods have
been applied to population-based dietary survey data, comparisons
indicate that 10 to 50 percent of respondents may be underreport-
ing their food (energy) intakes (Black et al., 1991; Briefel et al.,
1997; Johansson et al., 1998; Stallone et al., 1997) .
While the underreporting of energy intakes appears well docu-
mented, it is unclear how this affects the accuracy of self-reported
nutrient intakes. Research into this question is limited by the absence
of reliable reference biomarkers for intakes of many nutrients. Studies
in which the assessment of self-reported energy intake using the
doubly labeled water method has been combined with the measure-
ment of urinary nitrogen excretion to assess self-reported protein
J ' 1 I
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32
DIETARY REFERENCE INTAKES
intake suggest that energy intake may be more prone to under-
estimation than protein intake (Larsson et al., 2002~. Importantly,
these findings imply that all nutrients are not proportionally under-
reported; rather, particular foods or classes of foods must be selec-
tively underreported. When the reported intakes by individuals
classed as energy underreporters have been compared to those
whose energy intakes appear more plausible, underreporters have
often been found to report a lower percentage of energy from fat
(Becker and Welten, 2001; Becker et al., 1999; Briefel et al., 1997;
Goris et al., 2000~. Such comparisons have also indicated lower
reported consumption of particular classes of foods among under-
reporters (Becker and Welten, 2001; Krebs-Smith et al., 2000~. How
much one can infer about the nature of underreporting from these
studies hinges on the validity of the assumption that underreporters'
dietary patterns are the same as those not deemed to be under-
reporting. Nonetheless, it would appear overly simplistic to assume
that the nutrient intakes of individuals who systematically under-
report their energy intakes are underreported to the same degree.
The implications of underreporting for dietary assessment and
planning are profound given the need to rely on self-reported
dietary intakes for information about usual intake patterns. Because
individuals' intakes of energy and nutrients are intertwined, the
systematic underestimation of true usual energy intakes for some
proportion of the population is likely to mean an underestimation
~ , . , . , . 11 By.. . .~1 , , .. , ~ . ~
ot nutrient Intakes as well. lhIS IS Illustrated In a recent analysts ot
data from a Swedish population survey in which the proportion of
individuals with nutrient intakes below the average requirement
decreased substantially when individuals reporting "implausibly or
dubiously low energy intakes" (defined as EI/BMReS~ < 1.10 and
1.10 to 1.34, respectively, with EI estimated from a 7-day food
record) were excluded from the analysis (Becker and Welten, 2001) .
Planners are currently limited as to what they can do to correct
problems of underreporting. The application of EI/BMReS~ thresh-
olds to identify underreporters can be problematic, given the need
to make assumptions about individuals' usual physical activity levels
(often in the absence of good measures of physical activity) and the
error inherent in estimates of BMR (an error that is compounded
when BMR is calculated using self-reported weight and height).
Further, it cannot be assumed that all those with reported energy
intakes above the chosen EI/BMReS~ threshold have accurately
reported their intakes. Even if underreporters are somehow identi-
fied, the exclusion of their data from population-level assessments
of nutrient adequacy clearly threatens the ability to generalize assess-
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INTRODUCTION TO DIETARY PLANNING
33
ment results to the population as a whole. This is because it cannot
be assumed that the cliets of inclivicluals iclentifieci as unclerreporters
are identical to those not so iclentifieci.
Well-accepteci, valiciateci methods to statistically correct for the
effects of underreporting on the estimated distribution of usual
intakes are presently lacking. The statistical procedures proposed
to adjust intake distributions for within-person variation in intake
(e.g., NRC, 1986; Nusser et al., 1996) do not correct for systematic
errors in reporting. Application of the residual method of energy
adjustment (Willett and Stampfer, 1986) to nutrient distributions
has been proposed as one means to recluce the bias associated with
energy underreporting without excluding the ciata of unclerreporters
in some kinds of epiclemiological analyses (Stallone et al., 1997~.
This adjustment method, however, floes not provide an appropriate
correction of underreporting for clietary intake ciata to be used in
assessment and planning applications of the DRIB. Energy acljust-
ment methods cannot eliminate bias clue to selective underreporting
of foocis; instead these methods effectively "assume" that nutrients
have been unclerreporteci in direct proportion to energy. Further,
energy adjustment floes not provide corrected estimates of absolute
intake. Thus, energy-acljusteci ciata are not useful in assessments of
nutrient acloquacy.
In summary, energy underreporting is clearly a serious problem
in clietary surveys; it limits the accuracy with which planners can
estimate usual energy and nutrient intakes in population groups of
interest. Given the current absence of inexpensive, valiciateci meth-
ods to readily identify underreporting in dietary intake surveys and
statistical methods to correct for underreporting in self-reported
energy and nutrient intakes, planners are severely limited in their
ability to aciciress this problem.
This problem not only highlights the importance of employing
thorough, standardized procedures to collect dietary data, but it
also flags the urgent need for more research into statistical methods
to analyze and adjust for underreporting in self-reported intake
data. In interpreting the results of dietary assessments prior to
determining planning goals, planners should look to other sources
of data on nutritional status (e.g., anthropometric, clinical, or bio-
chemical assessments) for corroborating evidence. In interpreting
dietary assessment results, planners may also find it useful to esti-
mate the extent of energy underreporting in their data by applying
factorial methods to compare reported energy intakes with estimates
of energy expenditure. However, the crudeness of these estimates
should be recognized. Until better methods of identification and
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34
DIETARY REFERENCE INTAKES
adjustment are clevelopeci, it is not recommencleci that ciata acljust-
ments be undertaken.
Planners can use clietary intake ciata from national surveys, but
should remain aware of the inaccuracies of the ciata when setting
intake goals baseci on the DRIs and assessing achievement of those
goals.
Representative terms from entire chapter:
reference intakes
