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

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levels of intake, comparing responses to determine
which results in a more “adequate” diet relative to the
criterion or indicator of adequacy chosen. Although it
is possible to compare two levels of intake, given the
types of variation that are independent of the level of
nutrient consumed (see variability in requirements section,
above), at least three levels of intake of a nutrient
should be evaluated in the same individual.
Data can then be evaluated for the parameters that
best fit the data [18]; for example, two models currently
used for individual amino acid requirements include
fitting a smooth regression curve and estimating where
it intersects the zero-balance line [19], and fitting a
regression curve with an inflection point and estimating
where that point lies [20]. Unfortunately, other than
protein [21] and some of the amino acids [22], there
are few nutrients for which such data are available for
analysis in this way.
In evaluating protein requirements for children in
the DRI process [10], it was necessary to group data
for those aged 9 months through 14 years, since only
seven studies could be identified in which individual
data were provided and that could be used to obtain a
regression curve. These studies were published from
1980 through 1992, and no studies published since
then were available. This analysis included a total of
53 subjects from the seven studies from which data
on multiple levels were available, plus an additional
three studies with a total of 42 subjects for whom only
group data were provided. It is of interest that only 16
of the total of 95 children were over the age of 5 years,
and almost all were boys (based on the data in the
individual publications included, the number of girls
could have been as high as 11 or as low as 2). The diets
tested in these studies were not standardized:Some
were animal-based (milk, egg), some were mixed (rice
and fish; beans, wheat, milk), and some were vegetable
(soybeans, rice and beans), and they came from geographically
diverse areas: China, Chile, Guatemala, and
the Philippines. Differentiation between boys and girls,
particularly during puberty, was only possible relative
to the amount of protein estimated for growth, and not
for maintenance [10].
Protein is one of the most studied nutrients, given
its importance in normal growth in infants and young
children and its frequent lack in the traditional diets
of many developing countries. The above example
demonstrates that, in spite of this, useful data to
obtain requirement estimates, let alone estimates of
the amount needed for growth in children, are woefully
inadequate.
Publication bias
Although estimates of human requirements are based
on published data, among the assumptions made in
reviewing such studies is that the published literature
reflects all the data that are worth reviewing. Par-
ticularly where equivocal results occur, the tendency of
journals to publish papers only if the results reported
are significant at the conventional level of p < .05 [22]
means that there may be a tendency of journals to reject
research studies as underpowered when differences
do not appear statistically significant. Meta-analyses
of studies related to cancer that have been published
versus all studies related to cancer have demonstrated
a preference for reporting only endpoints that produce
the best results [23]; whether this is true of nutrient
requirements is unknown.
Nutrient–nutrient interactions
Although it is not usually evaluated in carefully controlled
double-blind studies, the influence of other
nutrients on absorption and metabolism of the nutrient
under study is an important factor to consider in
evaluating data from different studies. Bioavailability
issues (see Gibson [11]) can also influence the data and
need to be carefully considered.
Energy requirements
As briefly described by Murphy and Vorster [2] in this
issue, estimating energy requirements represents a special
situation when NIVs are being developed. Unlike
the case with other nutrients, the adequacy (and excess)
of energy needs are readily assessed by individuals from
changes in body weight. Also unlike the case with other
nutrients, physiological mechanisms provide immediate
information to individuals that intake should be
increased or curtailed; thus, energy intake is not independent
of energy requirements, one of the statistical
assumptions upon which the use of the ANR is based
(see Murphy and Vorster [2]). Since estimates of energy
requirements are needed for program development
and for planning diets, somewhat different steps are
followed both to estimate energy requirements and to
then apply them to individuals and groups.
Energy requirement criteria
A. A. Yates
As with nutrients, the body can metabolically adapt to
lower levels of energy intake on a chronic basis. This
has been studied recently in some detail [24]. The
definition accepted by international working groups of
the amount needed to meet energy requirements can
be used as defining what is “adequate” for humans: the
amount needed to balance energy expenditure in order
to maintain a body size, body composition, and level of
physical activity consistent with good health [24]. This
includes the energy needed for optimal growth and
development in children, deposition of tissue during
pregnancy, and normal lactation.
The recommended levels of energy intake for individuals
are the levels that provide adequate energy to