Apri! 1998: S5-S9
Process and Development of Dietary Reference Intakes: Basis,
Need, and Application of Recommended Dietary Allowances
Allison A. Yates
Dr. Yates is Director of the Food and Nutrition
Board, Institute of Medicine, National Academy of
Sciences, Washington, DC 20418, USA.
Nutrition Reviews, Vol. 56, No. 4
sentation from Canadian scientists, a set of dietary reference intakes, which will include estimated average requirements (EARS),RDAs for individuals, and tolerable upper
limits of intake (ULs). The report on the first group of
nutrients (calcium, phosphorus, magnesium, vitamin D,
and fluoride), to be evaluated under the expanded framework, is expected to be issued in late spring 1998.
Note added in proo$ This report was issued in August 1997 and included an additional recommended intake level, adequate intake (AI).
Overview
NAS is a nonprofit, private, honorific organization chartered by the US Congress in 1863 to provide nonbiased
analysis of scientific issues of interest to the federal government. The FNB, since it was formed in 1940 as aunit of
the National Research Council of the NAS, has periodically reviewed the scientific literature and provided guidance to the federal government and others about dietary
recommendationsand issues of nutrition, food safety, and
health. Since 1990the FNB has been a division of the Institute of Medicine, which operates as an arm of NAS.
In 1941, when first established, the RDAs of the FNB
were based partially on a few experimentally determined
nutrient requirements but primarily on observations of
nutrient intakes from usual food patterns that appeared to
be adequate for maintaining health and preventing known
deficiencies. They were established as a goal for good
nutrition and a yardstick to measure progress.’
In the last three editions of the RDAs, the working
definition of the RDAs has been the “levels of intake of
essential nutrients considered, in the judgment of the FNB
on the basis of available scientific knowledge, to be adequate to meet the known nutritional needs of practically
all healthy persons.”24The first recommendations,in 1941,
were for energy; protein; calcium; iron; vitamins A, C, and
D; thiamin; riboflavin; and niacin. Over the years, additional nutrients have been added, so that the 10th edition4
contained recommendations and safe intakes for 26 nutrients plus energy (Figure 1). These recommendationshave
been developed by noted nutrition scientists brought together by NAS and as such represent quantitative advice
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Since 1940,the Food and Nutrition Board of the National
Academy of Sciences of the United States (NAS) has developed and periodically published recommended dietary
allowances (RDAs). RDAs have been used as the scientific basis for federal nutrition and food policy in the United
States. When first developed, RDAs were intended as
allowances that would meet the nutritional needs of most
healthy people; they were designed for planning diets to
prevent nutrient deficiencies in groups. They have come
to be used for many other purposes, such as food labeling
and food selection guides for healthy diets; they are the
basis of assessment of the adequacy of dietary intakes in
national surveys, and they serve as the basis for food
security programs such as food stamps and supplemental
foods provided to low-income citizens.
As scientific knowledge about diet and health has
increased, technology has improved to allow measurement of small changes in individual adaptation to consumption of various levels of nutrients. Chronic diseases
or conditions that had been difficult to ascribe to inadequate or excess consumption of a specific nutrient have
been found to be closely linked to diet or nutrient intake.
To include these possible relationships in the definition
of “adequacy” used to establish dietary allowances, the
NAS Food and Nutrition Board (FNB) has expanded its
framework for determining dietary allowances. Also, because of increased consumption of nutrients in concentrated form, either singly or in combination with others
outside of the context of food, and because of the use of
fortification or enrichment of foods, the FNB is also examining data regarding the extent to which excess nutrient
intakes increase the risk of adverse or toxic effects. Thus,
where adequate data are available, a reference intake level
considered “safe” will be established.
The FNB has been reviewing these issues since 1991
and is currently in the process of developing, under an
expanded framework that will be described and with repre-
Recommended Dietary
Allowances 1989
0
Energy
0
Protein
0
7 minerals (Ca, Fe,
@
0
Mg, Zn, I , Se)
11 vitamins (A, C, D, B,, B, niacin, E, K,
B,, B,*,folate)
Safe and adequate daily dietary intakes
(biotin, pantothenate, Cu, Mn, F, Cr, Mo)
Figure 1. RDAs 1989.
Examples of Application of RDAs
Users:
Government-lndustry-AcademiaHealth Services
Uses:
Guide for procuring food supplies for
groups of healthy persons
Basis for planning meals for groups
Reference point for evaluating the
dietary intake of population
subgroups
Component of food and nutrition
education programs
Reference point for the nutrition
labeling of food and dietary
supplements
Figure 2. Examples of application of RDAs.
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to professionals about the amounts of nutrients thought
adequate for almost all of the population group for whom
they are intended. Dietary guidelines within the United
States represent qualitative advice to the public about
diet and prevention of chronic d i ~ e a s eWithin
.~
the United
States and Canada, dietary guidelines have-been based
on recommended nutrient intakes.
Over the years, because of the need to have some
basis for dietary planning and assessment, the RDAs have
been applied in a number of instances (Figure 2). They are
currently used as the basis or guide for procuring food
supplies for groups of healthy people, such as the miliin supplemental feeding programs for at-risk groups;'
as the basis for planning meals for groups; as the reference point for evaluating the dietary intake of population
subgroups; as the scientific basis for food and nutrition
education programs such as the US Department of Agriculture food guide pyramid; and as a reference point for
nutrition labeling of food and dietary supplements.
Although the RDAs have been considered primarily
as recommendations for preventing deficiency states, as
new information has become available various editions of
the RDAs have included statements about nutrient intake
and decreasing the risk of various chronic diseases. For
example, recommendations published in 1968 discussed
the relationship of dietary fat and cardiovascular disease,*
whereas recommendations published in 1974 stated that
individuals at risk for coronary heart disease should follow the American Heart Association dietary recommendations for fat intake?
As scientific knowledge about diet and health has
increased, other chronic diseases or conditions that had
been difficult to ascribe to inadequate or excess consumption of a specific nutrient have been found to be linked to
diet or nutrient intake. In previous FNB publications? as
in other major reports about the relationship between diet
and health,1° the conclusions are based on varied data
that typically include observed intakes in healthy populations, epidemiologic observations, balance studies, depletiodrepletion studies, and dose responses over time. The
following criteria for causal relationships have be& well
de~cribed:~J'
Strength of association.
Dose-response relationship.
Temporally correct association.
Consistency of association.
Specificity of association.
Biologic plausibility.
Given individual variability in response and the length
of time necessary to see measurable responses due to
long-term intakes, it is often difficult to obtain scientific
agreement about the quantitative relationships. To propose that these relationships be included in the definition
of adequacy used to establish RDAs, the FNB released
for comment an expanded framework for approaching the
determination of dietary allowances.12This was a result of
asking the nutrition and scientific community for comments on the following key questions:
What factors limit the usefulness of RDAs in their current
form?
What new information exists that argues for a change
from current values?
Should concepts of disease prevention be included in the
RDAS?
How shouldrecommended levels be expressed?As single
numbers? As ranges? Should toxic levels be included?
Shouldthe RDAs deal with nutrient-nutrientrelationships?
Are there new food components that should be considered?
As a result of the comments received on the expanded
p
Safe range of intake
X
-- Os
9.
Observed levelof intake
Figure 3. Model for DRIs.
Nutrition Reviews, Vol. 56, No. 4
Current Status of DRI Activity
The FNB has been reviewing these concepts since 1991,
in part on the basis of the most recent Dietary Reference
Valuesfor Food Energy and Nutrientsfor the UnitedKingdom.l4 Under the expanded framework described here and
with representation from Canadian scientists, the first set
Increasingintake
2SD
.
Recommended
Dietary
Allowance (RDA)
EstimatedAverage Requirement (EAR)
Figure 4. Model for dietary reference values.
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framework, the FNB has developed an expanded process
for developingdietary recommendations. Where adequate
data exist, the reductions of risk of chronic disease and
developmental abnormalities are incorporated. Thus, a
review of food components that may not meet typical criteria for essential nutrients, but for which there may be a
beneficial effect on health, is also included. To be more
responsive to the various uses to which past RDAs have
been applied, multiple reference levels are provided. The
overall process is called dietary reference intakesfDRIs).
DRIs include at least three reference points (Figure
3): EAR, RDA, and UL. EAR is the average requirement
for healthy individuals in which a functional or clinical
assessment has been conducted and measures of adequacy have been made at a specified level of dietary
intake. The data available are limited because few human
studies have been done, particularly in population groups
such as children and the elderly. EAR is the amount of
intake of a nutrient at which about one-half of subjects
would have their needs met and one-half would not.
It must be stressed that the most important component of this analysis is the determination of “Adequate
for what?’ This point is often ignored in discussions of
dietary recommendations,but it is fundamental to subsequent uses of the estimate. It involves being able to ascertain for a given intake a marker or indicator of adequacy
that is sensitive to the dietary intake over a reasonable
time and that is directly related to a specific outcome by
virtue of meeting the criteria for diet and disease relationships indicated above. Thus, for example, if a minimum
amount of hemoglobin is considered to be the cutoff for
adequacy, it should be related to a functional outcome,
such as anemia, which results from an inadequate supply
of oxygen to tissues because of a lack of red blood cells or
hemoglobin. It is thus possible to have a number of indicators of adequacy, each of which may be related to one
functional outcome (for example, red blood cell count versus hemoglobin content or packed cell volume) just as it
is possible to have more than one functional outcome
(anemia versus a minimum amount of iron stored as measured by total iron binding capacity). It is necessary first
to obtain the scientific judgment of experts to determine
the best indicators of adequacy for each defined level of
nutriture and then to determine which level ofaxutrhre is
most appropriate to use, assuming good health is the desired outcome.
Once the EAR is determinedand some estimate of the
variation in requirements is made (from experimental evidence or from interpolation of other data), a second reference intake is develope-he
RDA, which is defined as
the amount needed to meet the requirements of nearly all
(97-98%) of the healthy population of individuals for
whom it is developed. To calculate the MIA, the EAR is
increased by 2 standard deviations (or twice the coefficient of variation) of the estimated average requirement
(Figure 4).The RDA should serve as a goal for intake for
individuals. It should not serve as the benchmark of adequacy in the diets of populations, which is often a misuse of numbers derived in the past. The EAR has been
proposed to be used as the basis for assessing populations once knowledge of the variation in intake among the
population is included in the ana1y~is.I~
Thus, although
the EAR is not used as a reference intake for individuals,
its two purposes are to develop a reference intake to serve
as a goal for an individual (RDA) and a reference intake
with which to assess a population’s intake.
Because of increased consumption of nutrients in
concentrated form, either singly or in combination with
others outside of the context of food, and because oflhe
increased use of fortification or enrichment of foods, the
FNB has also included in the framework a model for examining the data regarding the extent to which excess nutrient intakes increase the risk of adverse or toxic effects.
Thus, where adequate data are available, a reference intake level for safety will be established-the UL.
nents (Figure 5). It is hoped that, as funding becomes
available, the subcommittee on applications and uses of
DRIs will be able to start work to provide guidance
scientifically valid uses of the various DRIs in both assessment of the diets of populations and in the use of
DRIs as goals in population-based dietary guidelines.
Note added in proofi The folate and B vitamins report will be released in April 1998. A new panel to look
at dietary antioxidants and related compounds has been
named, and its report is expected in fall 1998.
National Research Council. Recommended dietary
allowances. Washington, DC: National Academy
Press, 1941
2. National Research Council. Recommended dietary
allowances, 8th ed. A report of the Committee on
Dietary Allowances and Committee on Interpretation
of the Recommended Dietary Allowances, Food and
Nutrition Board. Washington, DC: National Academy
Press, 1974
3. National Research Council. Recommended dietary
allowances, 9th ed. A report of the Committee on
Dietary Allowances, Food and Nutrition Board. Washington, DC: National Academy Press, 1980
4. National Research Council. Recommended dietary
allowances, 10th ed. A report of the Subcommittee
on the Tenth Edition of the RDAs, Food and Nutrition
Board. Washington, DC: National Academy Press,
1989
5. US Department of Agriculture, Agricultural Research
Service, Dietary Guidelines Advisory Committee.
Report of the Dietary Guidelines Advisory Committee on the dietary guidelines for Americans, 1995, to
1.
-
Committee on Dietary Reference Intakes
Other food components
Panel
Figure 5. DRI framework of panels.
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of DRIs should be completed by late 1997.This report will
include EARS,RDAs for the individual, and ULs.
The project has been organized into two subcommittees and seven panels of nutrient experts under the oversight of the Standing Committee on Dietary Reference Intakes of the FNB (Figure 5 ) . The standing committee has
nine members, with a nonvoting liaison from the govemments of the United States and Canada. To develop scientific bases for all reference intakes, many experts will be
involved; assuming there is adequate funding from both
public and private organizations, the project will take at
least 4 years. One subcommittee, which is composed of
nutritionists, clinicians, and toxicologists, has been given
the task of developing a model for risk assessment of high
intakes of nutrients; it will review the adverse effects of
high levels of intake of each nutrient or food component
according to the model that is developed and will derive
appropriate limits of intake.
The panel on calcium and related nutrients (the first
group of nutrients to be reviewed includes calcium, phosphorus, magnesium, vitamin D, and fluoride), which is
composed of 10 experts, was scheduled to com>lete its
work in early spring 1997, and the report issued by the
DRI committee was scheduled for late spring. A second
panel-the panel on folate, vitamin B12,vitamin B,, other
B vitamins, and choline-has been named and will develop the basis for DRIs for those nutrients, with a report
to be issued in spring 1998. Five other panels will be appointed, one of which will focus on other food compo-
10. US Department of Health and Human Services. The
11.
12.
13.
14.
surgeon general’s report on nutrition and healthDHHS (PHS) PublicationNo. 88-50210. Washington,
DC: US Government Printing Office, 1988
Hill AB. Principles of medical statistics, 9th ed. New
York: Oxford University Press, 1971
Instituteof Medicine, Food and Nutrition Board. How
should the recommended dietary allowances be revised? Washington, DC: National Academy Press,
1994
Beaton GH. Criteria of an adequate diet. in: Shils
RE, Olson JA, Shike M, eds. Modern nutrition in
health and disease, 8th ed. Philadelphia: Lea &
Febiger, 1994;1491-I 505
Committee on Medical Aspects of Food Policy. Dietary reference values for food energy and nutrients
for the United Kingdom. Report of the Panel on Dietary Reference Values of the Committee on Medical
Aspects of Food Policy. Departmentof Health, Report
on Health and Social Subjects, No. 41 London:
HMSO, 1991
The Food and Nutrition Board Standing Committee on the Scientific Evaluation of Dietary Reference Intakes is chaired by
Vemon R. Young (Massachusetts Institute of Technohogy); cochaired by John W. Erdman, Jr. (University of Illinois at UrbanaChampaign) and Janet C. King (USDA Western Human Nutrition Research Center); and includes Lindsay H. Allen (University of
California, Davis), Stephanie A. Atkinson (McMaster University), Johanna T. Dwyer (Frances Stem Nutrition Center), John D.
Femstrom (University of Pittsburgh School of Medicine), Scott M. Grundy (University of Texas Southwestern Medical Center at
Dallas), and Sanford A. Miller (University of Texas Health Science Center). The senior staff for the Institute of Medicine (IOM)
include Allison A. Yates, Project Director, Carol W. Suitor, and Sandra A. Schlicker. For further information, write FNB/IOM, 2101
Constitution Avenue, NW, Washington, DC 20418, or e-mail at [email protected].
Nutrition Reviews, Vol. 56, No. 4
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the Secretary of Health and Human Services and the
Secretary of Agriculture. Washington, DC: US Government Printing Office, 1995
Institute of Medicine, Food and Nutrition Board Committee on Military Nutrition Research. Nutritional
needs in cold and high altitude environments. Washington, DC: National Academy Press, 1996
Institute of Medicine, Food and Nutrition Board, Committee on the Scientific Evaluation of WIC Nutrition
Risk Criteria. WIC nutrition risk criteria, a scientific
assessment. Washington, DC: National Academy
Press, 1996
National Research Council. Recommended dietary
allowances, 7th ed. A report of the food and Nutrition
Board, Publication No. 1694. Washington, DC: National Academy Press, 1968
National Research Council. Diet and health: implications for reducing chronic disease risk. A report of
the Committee on Diet and Health, Food and Nutrition Board. Washington, DC: National Academy
Press, 1989