Implementing food-based dietary guidelines for - United Nations ...

Terminology and framework for nutrient intake values
Frequency distribution of individual
requirements of nutrient X in women
30–50 years old
3 A 6 B 9 10
ANR: based on selected indicator
or criterion of adequacy
Increasing intake of nutrient X
INL 98
FIG. 2. In this symmetrical distribution of the requirements
for a subgroup of the population (assume that it is for apparently
healthy, nonpregnant, nonlactating women aged 30
through 50 years, woman A requires approximately 3.5 U of
nutrient X (this is the lowest level of intake for her at which
the criterion of adequacy chosen is normal or functions normally);
other women require less, the same, or more. Woman
B requires more, about 7 U of nutrient X, to demonstrate the
same level of normal function of the criterion of adequacy
selected. The ANR is the average nutrient requirement (in
this example, ANR = 6 U) for this group of women; the ANR
is specific for the nutrient, the group to which it applies, and
the criterion chosen for adequacy. Note that the INL x is set
at 2 SD (SD ANR ) above the ANR, and in this case, if SD ANR =
2 U, INL 98 = 10 U. (ANR, average nutrient requirement; INL,
individual nutrient level)
convenience sample), or to environmental factors
that affect nutrient needs and may differ from those
in place during the evaluation of the nutrient requirements
in the individuals sampled, as well as a host of
other causes.
Often the usual nutrient requirements of all individuals
in a population are not known, so data on the
specific variation in requirements are not available. In
that case, a standard estimate of variance is used. If one
assumes that the distribution of requirements is symmetrical,
a coefficient of variation (CV) (the standard
deviation divided by the mean × 100) can be used to
estimate the variation. It is often assumed that nutrient
requirements have a symmetrical distribution and a
similar CV that is equal to about 10% (i.e., the standard
deviation is about 10% of the mean requirement) [8].
This assumption is based on extensive data on the variation
in basal metabolic rate [6]; a similar CV of 12.5%
was derived from data on the protein requirements of
adults [30].
Given the routinely small sample sizes from which
ANRs are determined, a default estimate of the variation
for nutrients is often adopted for use when there
is little information from which to obtain a reliable
estimate of the variance or standard deviation of the
S23
ANR. The default CV frequently used is 10% (CV ANR
= SD ANR /ANR). For many nutrients, there are enough
data from dose–response curves to determine an ANR,
but in many cases the observed variation in response
due to the small number of subjects for which the
requirements were derived was thought to include
errors sizable enough to prevent the observed variation
from being used as an estimate. Instead, the default CV,
i.e., 10%, is used.
For a few nutrients included in the US/Canadian
dietary reference intakes, CVs larger than 10% were
applied. In the cases of copper, molybdenum, and
niacin, 15% was used on the basis of the variability in
response observed in the studies used to determine the
ANR [4, 5]; for vitamin A, 20% was used on the basis of
the variability in the apparent half-life of vitamin A in
liver stores. For iodine, 20% was applied on the basis of
iodine turnover studies [5], and for carbohydrate, 15%
was used on the basis of observed variability in brain
glucose utilization [6].
Other nutrient intake values derived from
an ANR
After the ANR and variance in requirements have
been determined, an individual nutrient level x (INL x )
may be derived from the ANR and its distribution.
The subscript x refers to the percentile chosen for the
setting the INL. Often committees add 2 SD to the
observed ANR which will cover the needs of most (i.e.,
98%) individuals if the distribution of requirements is
symmetrical, and it can thus be used as the target for
an individual’s nutrient intake. This is the approach
used in the United Kingdom and the US/Canadian
reports, where this model for estimating multiple
nutrient references was first applied. In those cases,
the INL x would be an INL 98 ; those values are referred
to as the reference nutrient intake (RNI) and the recommended
dietary allowance (RDA) in the UK and
USA/Canadian reports, respectively [3–7, 10]: INL 98
= ANR + 2 SD ANR .
Individuals whose intake is equal to the INL 98 have
a 98% probability that their intake meets their needs.
One might also choose to have a recommended intake
at a lower level, such as 1.5 SD above the ANR, resulting
in a lower target intake for individuals, and a lower
probability of adequacy for individuals who achieve
this target (in this case, ANR + 1.5 SD ANR = 93%, rather
than 98%). One could also set the INL x at 2.5 SD above
the ANR, increasing the probability of adequacy to 99%
for individuals whose intakes are at the INL.
Since the INL x represents a nutrient goal for all
individuals in a specific country or region, committees
charged with establishing nutrient recommendations
for a country or region should choose the specific
multiple of the SD ANR they wish to use that is consistent