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1
Introduction to Dietary
Reference Intakes
Dietary Reference Intakes (DRIs) comprise a set of reference values
for specific nutrients, each category of which has special uses. The devel-
opment of DRIs expands on the periodic reports called Recommended Dietary
Allowances, published from 1941 to 1989 by the National Academy of
Sciences, and Recommended Nutrient Intakes, published by the Canadian gov-
ernment. This comprehensive effort is being undertaken by the Standing
Committee on the Scientific Evaluation of Dietary Reference Intakes of
the Food and Nutrition Board, Institute of Medicine, the National Academies,
in collaboration with Health Canada. See Appendix B for a description of
the overall process, its origins, and other relevant issues that developed as
a result of this new process.
WHAT ARE DIETARY REFERENCE INTAKES?
The reference values, collectively called the Dietary Reference Intakes
(DRIs), include the Estimated Average Requirement (EAR), Recommended
Dietary Allowance (RDA), Adequate Intake (AI), and Tolerable Upper Intake
Level (UL) (Box 1-1). Establishment of these reference values requires that a
criterion of nutritional adequacy be carefully chosen for each nutrient, and
that the population for whom these values apply be carefully defined.
A requirement is defined as the lowest continuing intake level of a
nutrient that, for a specific indicator of adequacy, will maintain a defined
level of nutriture in an individual. The chosen criterion or indicator of
nutritional adequacy upon which EARs and AIs are based is identified for
each nutrient. The criterion may differ for individuals at different life
stages. Particular attention is given throughout this report to the choice
21
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22 DIETARY REFERENCE INTAKES
BOX 1-1
Dietary Reference Intakes
Recommended Dietary Allowance (RDA): the average daily dietary nutrient
intake level sufficient to meet the nutrient requirement of nearly all (97 to 98 percent)
healthy individuals in a particular life stage and gender group.
Adequate Intake (AI): the recommended average daily intake level based on observed
or experimentally determined approximations or estimates of nutrient intake by a group
(or groups) of apparently healthy people that are assumed to be adequate—used when
an RDA cannot be determined.
Tolerable Upper Intake Level (UL): the highest average daily nutrient intake
level that is likely to pose no risk of adverse health effects to almost all individuals in
the general population. As intake increases above the UL, the potential risk of adverse
effects may increase.
Estimated Average Requirement (EAR): the average daily nutrient intake level
estimated to meet the requirement of half the healthy individuals in a particular life
stage and gender group.a
a In the case of energy, an Estimated Energy Requirement (EER) is pro-
vided. The EER is the average dietary energy intake that is predicted to
maintain energy balance in a healthy adult of a defined age, gender, weight,
height, and level of physical activity consistent with good health. In children
and pregnant and lactating women, the EER is taken to include the needs
associated with the deposition of tissues or the secretion of milk at rates
consistent with good health.
and justification of the criterion used to establish requirement values and
the intake levels beyond which the potential for increased risk of adverse
effects may occur.
CATEGORIES OF DIETARY REFERENCE INTAKES
Estimated Average Requirement1
The Estimated Average Requirement (EAR) is the daily intake value that is
estimated to meet the requirement, as defined by the specified indicator
1The 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 symmetrical distribution and would diverge if a distribution were skewed.
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I NTRODUCTION TO DIETARY REFERENCE INTAKES
or criterion of adequacy, in half of the apparently healthy individuals in a
life stage or gender group (see Figure 1-1). A normal or symmetrical distri-
bution (median and mean are similar) is usually assumed for setting the
EAR. At an intake level equal to the EAR, half of a specified group would
not have their nutritional needs met. This is equivalent to saying that
randomly chosen individuals from the population would have a 50:50
chance of having their requirement met at this intake level. This use follows
the precedent set by others who have used the term “Estimated Average
Requirement” for reference values similarly derived but meant to be applied
to population intakes (COMA, 1991).
The EAR’s usefulness as a predictor of an individual’s requirement
depends on the appropriateness of the choice of the nutritional status
indicator or criterion and the type and amount of data available. The general
method used to set the EAR is the same for all nutrients. The specific
approaches, which are provided in Chapters 5 through 10, differ since
each nutrient has its own indicator(s) of adequacy, and different amounts
and types of data are available for each.
The EAR serves three major functions: as the basis for the Recom-
mended Dietary Allowance (RDA), as the primary reference point for
Risk of Adverse Effects
Risk of Inadequacy
1.0 1.0
0.5 0.5
0.0 0.0
Observed Level of Intake
FIGURE 1-1 Dietary Reference Intakes. This figure shows that the Estimated Aver-
age Requirement (EAR) is the intake at which the risk of inadequacy is estimated
to be 0.5 (50 percent) to an individual. The Recommended Dietary Allowance
(RDA) is the intake at which the risk of inadequacy would be very small—only 0.02
to 0.03 (2 to 3 percent). At intakes between the RDA and the Tolerable Upper
Intake Level (UL), the risk of inadequacy and of excess are both estimated to be
close to 0.0. At intakes above the UL, the potential risk of adverse effects may
increase.
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24 DIETARY REFERENCE INTAKES
assessing the adequacy of estimated nutrient intakes of groups (IOM,
2000a), and, together with estimates of the variance of intake, in planning
for the intake of groups (see Chapter 13).
Recommended Dietary Allowance
The Recommended Dietary Allowance (RDA) is an estimate of the mini-
mum daily average dietary intake level that meets the nutrient require-
ments of nearly all (97 to 98 percent) healthy individuals in a particular
life stage and gender group (see Figure 1-1). The RDA is intended to be
used as a goal for daily intake by individuals as this value estimates an
intake level that has a high probability of meeting the requirement of a
randomly chosen individual (about 97.5 percent). The process for setting
the RDA is described below; it depends on being able to set an EAR and
estimating the variance of the requirement itself. Note that if an EAR
cannot be set due to limitations of the data available, no RDA will be set.
This approach differs somewhat from that used by the World Health
Organization, Food and Agriculture Organization, and International Atomic
Energy Agency (WHO/FAO/IAEA) Expert Consultation on Trace Elements
in Human Nutrition and Health (WHO, 1996). That publication uses the
term basal requirement to indicate the level of intake needed to prevent
pathologically relevant and clinically detectable signs of a dietary inadequacy.
The term normative requirement indicates the level of intake sufficient to
maintain a desirable body store, or reserve. In developing an RDA (and
Adequate Intake [AI], see below), emphasis is placed instead on the reasons
underlying the choice of the criterion of nutritional adequacy used to
establish the requirement. It is not designated as basal or normative.
Method for Setting the RDA When Nutrient Requirements Are
Normally Distributed
When the distribution of a requirement among individuals in a group
can be assumed to be approximately normal (or symmetrical), and a stan-
dard deviation (SD) of requirement (SDrequirement) can be determined, the
EAR can be used to set the RDA as follows:
RDA = EAR + 2 × SDrequirement.
If data about variability in requirements are insufficient to calculate an
SDrequirement for that specific nutrient in that population group, but nor-
mality or symmetry can be assumed, then a coefficient of variation (CV) of
10 percent will be assumed and the calculation becomes:
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I NTRODUCTION TO DIETARY REFERENCE INTAKES
RDA = EAR + 2 (0.1 × EAR) = 1.2 × EAR.
The assumption of a 10 percent CV is based on extensive data on the
variation in basal metabolic rate (FAO/WHO/UNA, 1985; Garby and
Lammert, 1984) and the CV of 12.5 percent estimated for the protein
requirements in adults (FAO/WHO/UNA, 1985). If there is evidence of
greater variation, a larger CV will be used. In all cases, the method used to
derive the RDA from the EAR is stated.
Since it is derived from the EAR, the RDA’s usefulness as a goal
depends on the choice of nutritional status indicator or criterion and the
type and amount of data available. Its applicability also depends on the
accuracy of the form of the requirement distribution and the estimate of
the variance of requirements for the nutrient in the population subgroup
for which it is developed.
For many of the macronutrients, there are few direct data on the
requirements of children. In this case, EARs and RDAs for children are
based on extrapolations from adult values. The methods for extrapolation
are described in Chapter 2.
Method for Setting the RDA When Nutrient Requirements Are Not
Normally Distributed
If the requirement of a nutrient is not normally distributed but can be
transformed to normality, its EAR and RDA can be estimated by trans-
forming the data, calculating the 50th (for the EAR) and the 97.5th per-
centiles (for the RDA), and transforming these percentiles back into the
original units. In this case, the difference between the EAR and RDA can-
not be used to obtain an estimate of the variance in the requirement (the
SD or CV) since skewing is present.
Where factorial modeling is used to estimate the distribution of a
requirement from the distributions of the individual components of the
requirement (maintenance and growth), as was done in the case of protein
and amino acid recommendations for children, it is necessary to add
(termed convolve) the individual distributions. Estimating the convolution
of two distributions in general is very difficult. However, this is easy to do
with normal distributions since the average requirement is simply the sum
of the averages of the individual component distributions, and an SD of
the combined distribution can be estimated by standard statistical tech-
niques. The 97.5th percentile can then be estimated. (For a discussion of
the method, see Appendix B.)
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26 DIETARY REFERENCE INTAKES
Adequate Intake
If sufficient scientific evidence is not available to calculate an EAR, a
reference intake called an Adequate Intake (AI) is provided instead of an
RDA. The AI is a value based on experimentally determined approxima-
tions or estimates of observed median nutrient intakes by a group (or
groups) of healthy people. In the judgment of the Standing Committee on
the Scientific Evaluation of Dietary Reference Intakes, the AI is expected
to meet or exceed the amount needed to maintain a defined nutritional
state or criterion of adequacy in essentially all members of a specific,
apparently healthy, population. Examples of defined nutritional states
include normal growth, maintenance of normal circulating nutrient values,
or other aspects of nutritional well-being or general health.
For young infants for whom human milk is the recommended sole
source of food for most nutrients for the first 4 to 6 months of life, the AI
is based on the daily mean nutrient intake of human milk in healthy, full-
term infants who are exclusively fed human milk. The goal may be differ-
ent for infants consuming infant formula for which the bioavailability of a
nutrient may be different from that in human milk. For adults, the AI may
be based on data from a single experiment, on estimated dietary intakes in
apparently healthy population groups, or on a review of data from differ-
ent approaches that, when considered alone, do not permit a reasonably
confident estimate of an EAR.
Comparison of the Recommended Dietary Allowance and the
Adequate Intake
There is much less certainty about an AI value than about an RDA
value. Because AIs depend on a greater degree of judgment than is applied
in estimating an EAR and subsequently an RDA, an AI may deviate signifi-
cantly from, and may be numerically higher than, an RDA. For this reason,
AIs must be used with greater care than is the case for RDAs. Also, an RDA
is usually calculated from an EAR by using a formula that takes into
account the expected variation in the requirement for the nutrient.
Both the AI and RDA are to be used as a goal for individual intake. In
general, the values are intended to cover the needs of nearly all apparently
healthy individuals in a life stage group. (For infants, the AI is the mean
intake when infants in the age group are consuming human milk. Larger
infants may have greater needs, which they meet by consuming more milk.)
The AI for a nutrient is expected to exceed the RDA for that nutrient, and
thus it should cover the needs of more than 97 to 98 percent of individuals.
The degree to which the AI exceeds the RDA is likely to differ among
nutrients and population groups. As with RDAs, AIs for children and ado-
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I NTRODUCTION TO DIETARY REFERENCE INTAKES
lescents may be extrapolated from adult values if no other usable data are
available.
For people who have diseases that increase specific nutrient require-
ments or who have other special health needs, the RDA and AI each may
serve as the basis for adjusting individual recommendations. Qualified
health professionals should adapt the recommended intake to cover higher
or lower needs.
Tolerable Upper Intake Level
The Tolerable Upper Intake Level (UL) is the highest level of daily nutri-
ent intake that is likely to pose no risk of adverse health effects for almost
all individuals in the specified life stage group (see Figure 1-1). As intake
increases above the UL, there is the potential for an increased risk of
adverse effects. The term tolerable was chosen to avoid implying a possible
beneficial effect. Instead, the term is intended to connote a level of intake
that can, with high probability, be tolerated biologically. The UL is not
intended to be a recommended level of intake, as there is no established
benefit for healthy individuals if they consume a nutrient in amounts
exceeding the recommended intake (the RDA or AI).
The UL is based on an evaluation conducted by using the methodology
for risk assessment of nutrients (see Chapter 4). The need for setting ULs
has arisen as a result of the increased fortification of foods with nutrients
and the use of dietary supplements by more people and in larger doses.
The UL applies to chronic daily use and is usually based on the total intake
of a nutrient from food, water, and supplements if adverse effects have
been associated with total intake. However, if adverse effects have been
associated with intake from supplements or food fortificants only, the UL
is based on nutrient intake from one or both of those sources only, rather
than on total intake. As in the case of applying AIs, professionals should
avoid very rigid application of ULs and first assess the characteristics of the
individual or group of concern (e.g., source of nutrient, physiological state
of the individual, length of sustained high intakes, etc.).
For some nutrients, data may not be sufficient for developing a UL.
This indicates the need for caution in consuming amounts greater than
the recommended intake; it does not mean that high intake poses no
potential risk of adverse effects.
The safety of routine, long-term intake above the UL is not well docu-
mented. Although members of the general population should be advised
not to routinely exceed the UL, intake above the UL may be appropriate
for investigation within well-controlled clinical trials. Clinical trials of doses
above the UL should not be discouraged as long as subjects participating
in these trials have signed informed consent documents regarding pos-
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28 DIETARY REFERENCE INTAKES
sible toxicity and as long as these trials employ appropriate, safe monitor-
ing of trial subjects.
DETERMINATION OF ADEQUACY
Adequacy
In the derivation of Estimated Average Requirements (EARs) or Ade-
quate Intakes (AIs), close attention has been paid to the determination of
the most appropriate indicators of adequacy. A key question is, Adequate
for what? In many cases, a continuum of benefits may be ascribed to various
levels of intake of the same nutrient. One criterion may be deemed the
most appropriate to determine the risk that an individual will become
deficient in the nutrient, whereas another may relate to reducing the risk
of a chronic degenerative disease, such as certain neurodegenerative dis-
eases, cardiovascular disease, cancer, diabetes mellitus, or age-related
macular degeneration.
Each EAR and AI is described in terms of the selected criterion or
indicator of adequacy. The potential role of the macronutrients in the
reduction of disease risk was considered in developing the EARs. With the
acquisition of additional data relating intake more directly to chronic dis-
ease or disability, more sensitive and reliable indicators or criteria may be
validated and thus the criterion for setting the EAR may change.
Role in Health
Unlike other nutrients, energy-yielding macronutrients can be used
somewhat interchangeably (up to a point) to meet energy requirements of
an individual. In this report, EARs or AIs have been provided for specific
macronutrients or components of these classes of macronutrients where
the data were adequate to establish a causal relationship between intake
and a specific function or chosen criterion of adequacy. However, for the
general classes of nutrients and some of their subunits, this was not always
possible; the data do not support a specific number, but rather trends
between intake and chronic disease identify a range. Given that energy
needs vary with individuals, a specific number was not deemed appropriate
to serve as the basis for developing diets that would be considered to
decrease risk of disease, including chronic diseases, to the fullest extent
possible. Thus Acceptable Macronutrient Distribution Ranges (AMDRs)
have been established for macronutrients as percentages of total energy
intake. These are ranges of macronutrient intakes that are associated with
reduced risk of chronic disease, while providing recommended intakes of
other essential nutrients.
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I NTRODUCTION TO DIETARY REFERENCE INTAKES
Because much of this evidence is based on clinical endpoints (e.g.,
coronary heart disease, diabetes, cancer, and obesity), which point to
trends rather than distinct endpoints, and because there may be factors
other than diet that may contribute to chronic disease, it is not possible to
determine a defined level of intake at which chronic disease may be pre-
vented or may develop. Therefore, an AMDR is not considered to be a
Dietary Reference Intake (DRI) that provides a defined intake level. An
AMDR is provided to give guidance in dietary planning by taking into
account the trends related to decreased risk of disease identified in epide-
miological and clinical studies.
AMDRs are expressed as percentages of total energy intake because
their requirements, in a classical sense, are not independent of each other
or of the total energy requirement of the individual. Each must be
expressed in terms relative to the others. A key feature of each AMDR is
that it has a lower and upper boundary, some determined mainly by the
lowest or highest value judged to have an expected impact on health.
Above or below these boundaries there is a potential for increasing the
risk of chronic diseases shown to effect long-term health. The macro-
nutrients and their role in health are discussed in Chapter 3, as well as in
Chapters 5 through 11.
PARAMETERS FOR DIETARY REFERENCE INTAKES
Nutrient Intakes
Each type of Dietary Reference Intake (DRI) refers to the average
daily nutrient intake of individuals over time. The amount consumed may
vary substantially from day-to-day without ill effects in most cases. More-
over, unless otherwise stated, all values given for Estimated Average
Requirements (EARs), Recommended Dietary Allowances (RDAs), Ade-
quate Intakes (AIs), or Acceptable Macronutrient Distribution Ranges
(AMDRs) represent the quantity of the nutrient or food component to be
supplied by foods from diets similar to those consumed in Canada and the
United States. Healthy subgroups of the population often have different
requirements, so special attention has been given to the differences due to
gender and age, and often separate reference intakes are estimated for
specified subgroups.
For some nutrients (e.g., trace elements), a higher intake may be
needed for healthy people if the degree of absorption of the nutrient is
unusually low on a chronic basis (e.g., because of very high fiber intake). If
the primary source of a nutrient is a supplement, a higher or lower per-
centage may be absorbed and so a smaller or greater intake may be
required, or an adverse effect may be demonstrated at a lower level of
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30 DIETARY REFERENCE INTAKES
intake. When this is an issue, it is discussed for the specific nutrient in the
section “Special Considerations.”
The DRIs apply to the apparently healthy population, and while the
RDAs and AIs are levels of intake recommended for individuals, meeting
these levels would not necessarily be sufficient for individuals who are
already malnourished. People with diseases that result in malabsorption
syndrome or who are undergoing treatment such as hemo- or peritoneal
dialysis may have increased requirements for some nutrients. Special
guidance should be provided for those with greatly increased nutrient
needs or for those with decreased needs such as energy due to disability or
decreased mobility. Although the RDA or AI may serve as the basis for
such guidance, qualified medical and nutrition personnel should make
necessary adaptations for specific situations.
Life Stage Groups
The life stage groups described below were chosen while keeping in
mind all the nutrients to be reviewed, not only those included in this
report. Additional subdivisions within these groups may be added in later
reports. If data are too sparse to distinguish differences in requirements by
life stage or gender group, the analysis provided in establishing the DRI
may be presented for a larger grouping.
Infancy
Infancy covers the period from birth through 12 months of age and is
divided into two 6-month intervals. Except for energy, the first 6-month
interval was not subdivided further because intake is relatively constant
during this time. That is, as infants grow, they ingest more food; however,
on a body-weight basis their intake remains nearly the same. During the
second 6 months of life, growth velocity slows, and thus daily nutrient
needs on a body-weight basis may be less than those during the first
6 months of life.
For protein, amino acids, carbohydrate, fat, and n-6 and n-3 poly-
unsaturated fatty acids, the average intake by full-term infants who are
born to healthy, well-nourished mothers and exclusively fed human milk
has been adopted as the primary basis for deriving the AI during the first
6 months of life. This is the model used for other nutrients as well. The
value established is thus not an EAR. The extent to which intake of human
milk may result in exceeding the actual requirements of the infant is not
known, and ethics of human experimentation preclude testing the levels
known to be potentially inadequate. Therefore, the AI, while determined
from the average composition of an average volume of milk consumed by
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I NTRODUCTION TO DIETARY REFERENCE INTAKES
this age group, is not an EAR in which only half of the group would be
expected to have their needs met.
Using the infant fed human milk as a model is in keeping with the
basis for estimating nutrient allowances of infants developed in the last
revisions of the RDAs (NRC, 1989) and Recommended Nutrient Intakes
(RNIs) (Health Canada, 1990). It also supports the recommendation that
exclusive human-milk feeding is the preferred method of feeding for
normal, full-term infants for the first 4 to 6 months of life. This recom-
mendation has also been made by the Canadian Paediatric Society (Health
Canada, 1990), the American Academy of Pediatrics (AAP, 1997), and in
the Food and Nutrition Board report, Nutrition During Lactation (IOM,
1991).
In general, for this report, special consideration was not given to pos-
sible variations in physiological need during the first month after birth, or
to the variations in intake of nutrients from human milk that result from
differences in milk volume and nutrient concentration during early lactation.
Specific DRIs to meet the needs of formula-fed infants are not proposed in
this report. The previously published RDAs and RNIs for infants have led
to much misinterpretation of the adequacy of human milk because of a
lack of understanding about their derivation for young infants. Although
they were based on human-milk composition and volume of intake, the
previous RDA and RNI values allowed for lower bioavailability of nutrients
from nonhuman milk. However, where warranted, information discussing
specific changes in bioavailability or source of nutrients for use in develop-
ing formulations is included in the “Special Considerations” section of
each chapter.
Ages 0 Through 6 Months. To determine the AI value for infants ages 0
through 6 months, the mean intake of a nutrient was calculated by multi-
plying the average concentration of the nutrient in human milk produced
during the second through sixth month of lactation (derived from con-
sensus values from several reported studies [Atkinson et al., 1995]) by the
average volume of milk intake of 0.78 L/d as reported from studies of full-
term infants by test weighing (Butte et al., 1984; Chandra, 1984; Hofvander
et al., 1982; Neville et al., 1988). Because there is variation in both of these
measures, the computed value represents the mean. It is assumed that
infants will have adequate access to human milk and that they will con-
sume increased volumes as needed to meet their requirements for mainte-
nance and growth.
Ages 7 Through 12 Months. The reference body-weight method that has
been used in previous DRI reports to extrapolate the AI for infants 0
through 6 months to an AI for older infants in the absence of direct data
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32 DIETARY REFERENCE INTAKES
on older infants (IOM, 1997) is not appropriate for dietary fats or carbo-
hydrates. This is because the amount of energy required on a body-weight
basis is significantly lower during the second 6 months of life, due largely
to the slower rate of weight gain/kg of body weight. Therefore, the basis of
the AI values derived for this age category for dietary fats and carbo-
hydrates was the sum of the specific nutrient provided by 0.6 L/d of human
milk, which is the average volume of milk reported from studies in this age
category (Heinig et al., 1993), and that provided by the usual intake of
complementary weaning foods consumed by infants in this age category
(Specker et al., 1997). This approach is in keeping with the current recom-
mendations of the Canadian Paediatric Society (Health Canada, 1990),
the American Academy of Pediatrics (AAP, 1997), and Nutrition During
Lactation (IOM, 1991) for continued feeding of human milk to infants
through 9 to 12 months of age with appropriate introduction of solid
foods.
Toddlers: Ages 1 Through 3 Years
Two points were primary in dividing early childhood into two groups.
First, the greater velocity of growth in height during ages 1 through 3 years
compared with ages 4 through 5 years provides a biological basis for divid-
ing this period of life. Second, because children in the United States and
Canada begin to enter the public school system starting at age 4 years,
ending this life stage prior to age 4 years seemed appropriate so that food
and nutrition policy planners have appropriate targets and cutoffs for use
in program planning.
Data are sparse for indicators of nutrient adequacy on which to derive
DRIs for these early years of life. In these cases, extrapolation using the
methods described in Chapter 2 has been employed.
Early Childhood: Ages 4 Through 8 Years
Major biological changes in velocity of growth and changing endo-
crine status occur during ages 4 through 8 or 9 years (the latter depending
on onset of puberty in each gender); therefore, the category of 4 through
8 years of age is appropriate. For many nutrients, a reasonable amount of
data is available on nutrient intake and various criteria for adequacy (such
as nutrient balance measured in children 5 through 7 years of age) that
can be used as the basis for the EARs and AIs for this life stage group.
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I NTRODUCTION TO DIETARY REFERENCE INTAKES
Puberty/Adolescence: Ages 9 Through 13 Years and
14 Through 18 Years
Because current data support younger ages for pubertal development,
it was determined that the adolescent age group should begin at 9 years.
The mean age of onset of breast development (Tanner Stage 2) for white
girls in the United States is 10.0 ± 1.8 (standard deviation) years; this is a
physical marker for the beginning of increased estrogen secretion
(Herman-Giddens et al., 1997). In African-American girls, onset of breast
development is earlier (mean 8.9 years ± 1.9). The reason for the observed
racial differences in the age at which girls enter puberty is unknown. The
onset of the growth spurt in girls begins before the onset of breast devel-
opment (Tanner, 1990). The age group of 9 through 13 years allows for
this early growth spurt of girls.
For boys, the mean age of initiation of testicular development is 10.5
to 11 years, and their growth spurt begins two years later (Tanner, 1990).
Thus, to begin the second age category at 14 years and to have different
EARs and AIs for girls and boys for some nutrients at this age seems bio-
logically appropriate. All children continue to grow to some extent until as
late as age 20 years; therefore, having these two age categories span the
period of 9 through 18 years of age seems justified.
Young Adulthood and Middle-Aged Adults: Ages 19 Through 30
Years and 31 Through 50 Years
The recognition of the possible value of higher nutrient intakes dur-
ing early adulthood on achieving optimal genetic potential for peak bone
mass was the reason for dividing adulthood into ages 19 through 30 years
and 31 through 50 years. Moreover, mean energy expenditure decreases
during this 30-year period, and needs for nutrients related to energy
metabolism may also decrease. For some nutrients, the DRIs may be the
same for the two age groups. However, for other nutrients, especially those
related to energy metabolism, EARs (and RDAs) are likely to differ for
these two age groups.
Adulthood and Older Adults: Ages 51 Through 70 Years and
Over 70 Years
The age period of 51 through 70 years spans the active work years for
most adults. After age 70, people of the same age increasingly display
variability in physiological functioning and physical activity. A comparison
of people over age 70 who are the same chronological age may demon-
strate as much as a 15- to 20-year age-related difference in level of reserve
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34 DIETARY REFERENCE INTAKES
capacity and functioning. This is demonstrated by age-related declines in
nutrient absorption and renal function. Because of the high variability in
functional capacity of older adults, the EARs and AIs for this age group
may reflect a greater variability in requirements for the older age catego-
ries. This variability may be most applicable to nutrients for which require-
ments are related to energy expenditure.
Pregnancy and Lactation
Recommendations for pregnancy and lactation may be subdivided
because of the many physiological changes and changes in nutrient need
that occur during these life stages. In setting EARs and AIs for these life
stages, however, consideration is given to adaptations to increased nutri-
ent demand, such as increased absorption and greater conservation of
many nutrients. Moreover, nutrients may undergo net losses due to physi-
ological mechanisms regardless of the nutrient intake. Thus, for some
nutrients, there may not be a basis for EAR values that are different during
these life stages than those for nonpregnant or nonlactating women of
comparable age.
Reference Heights and Weights
Use of Reference Heights and Weights
Reference heights and weights are useful when more specificity about
body size and nutrient requirements are needed than that provided by life
stage categories. For example, while the EAR may be developed for the 4-
to 8-year-old age group, a small 4-year-old child may be assumed to require
less than the EAR for that age group, whereas a large 8-year-old may
require more than the EAR. Based on the model for establishing RDAs,
however, the RDA (and for that matter, an AI) should meet the needs of
both.
In some cases, where data regarding nutrient requirements are
reported on a body-weight basis, it is necessary to have reference heights
and weights to transform the data for comparison purposes. Frequently,
where data regarding adult requirements represent the only available data
(e.g., on adverse effects of chronic high intakes for establishing Tolerable
Upper Intake Levels [ULs]), extrapolating on the basis of body weight or
size becomes a possible option to providing ULs for other age groups.
Thus, for this and other reports, when data are not available, the EAR or
UL for children or pregnant women may be established by extrapolation
from adult values on the basis of body weight.
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TABLE 1-1 New Reference Heights and Weights for Children and Adults in the United States
Previous Median New Median New Median
Body Mass Indexa Body Mass Reference New Reference
Sex Age (kg/m2) Indexb (kg/m2) Height,b cm (in) Weight,c kg (lb)
Male, Female 2–6 mo — — 62 (24) 6 (13)
7–12 mo — — 71 (28) 9 (20)
1–3 y — — 86 (34) 12 (27)
4–8 y 15.8 15.3 115 (45) 20 (44)
Male 9–13 y 18.5 17.2 144 (57) 36 (79)
14–18 y 21.3 20.5 174 (68) 61 (134)
19–30 y 24.4 22.5 177 (70) 70 (154)
Female 9–13 y 18.3 17.4 144 (57) 37 (81)
14–18 y 21.3 20.4 163 (64) 54 (119)
19–30 y 22.8 21.5 163 (64) 57 (126)
a Taken from male and female median body mass index and height-for-age data from the Third National Health and Nutrition Examina-
tion Survey (NHANES III), 1988–1994; used in earlier DRI reports (IOM, 1997, 1998, 2000a, 2000b, 2001).
b Taken from new data on male and female median body mass index and height-for-age data from the Centers for Disease Control and
Prevention (CDC)/National Center for Health Statistics (NCHS) Growth Charts (Kuczmarski et al., 2000).
c Calculated from CDC/NCHS Growth Charts (Kuczmarski et al., 2000); median body mass index and median height for ages 4 through
19 years.
35
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36 DIETARY REFERENCE INTAKES
New Reference Heights and Weights
As is described in Appendix B, the DRI framework is an iterative pro-
cess that was undertaken in 1994. At that time, reference heights and
weights used in the DRI reports for the U.S. and Canadian populations
were developed based on data from the Third National Health and Nutri-
tion Examination Survey on body mass index (BMI) for children and
young adults (IOM, 1997). With the recent publication of new U.S.-based
growth charts for infants and children and the introduction of BMI rec-
ommendations for adults (Kuczmarski et al., 2000), reference heights and
weights for adults and children have been updated. Besides being more
current, these new reference heights and weights are more representative
of the U.S. population. Table 1-1 provides these updated values. Appendix B
includes information about the reference values that were used in the
earlier DRI reports.
SUMMARY
Dietary Reference Intakes (DRIs) is a generic term for a set of nutrient
reference values that include the Estimated Average Requirement, Recom-
mended Dietary Allowance, Adequate Intake, and Tolerable Upper Intake
Level. In addition, to provide guidance on the appropriate macronutrient
distribution thought to decrease risk of disease, including chronic disease,
Acceptable Macronutrient Distribution Ranges are established for the
macronutrients. These reference values have been developed for life stage
and gender groups in a joint U.S. and Canadian activity.
This report—one volume in a series—covers the DRIs for the dietary
macronutrients: carbohydrate, fiber, fat, cholesterol, protein, and amino
acids. It also provides recommendations for physical activity and energy
expenditure to maintain health and decrease risk of disease.
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Representative terms from entire chapter:
reference intakes
