Dietary Reference Standards 125dations. Their preferred term, nutrient intake value
(NIV), refers to dietary intake recommendations
based on research data; the term “nutrient” was chosen
in order to distinguish these from dietary compo-
nents such as cereals, and the term “value” is intended
to emphasize the potential usefulness for both assess-
ing dietary adequacy (and hence dietary planning)
and policy-making. The individual nutrient level
(INLx) is fl exible, in that x refers to the chosen per-
centile of the population for whom this intake is suf-
fi cient; for example 98% (mean or median requirement
- 2 SDs), written as INL 98 , but it could be set lower in
the case of certain nutrients.
Changes in conceptual approach
When a committee sits to make a recommendation
for a standard in relation to nutrient intakes, it begins
with a distribution of requirements. In the past,
although the choice of criteria for requirement might
vary between committees, the orientation was always
the same: requirements were set at a level that should
prevent defi ciency symptoms. More recently, the
concern for health promotion through diet has led to
the introduction of the concept of optimal nutrition,
in which the optimal intake of a nutrient could be
defi ned as that intake that maximizes physiological
and mental function and minimizes the development
of degenerative diseases. It should be borne in mind
that, although this may appear simple enough to
defi ne in the case of single nutrients, things clearly
become more complex when considering all nutrients
together, in all possible physiological situations.
Genetic variability may also, increasingly, be taken
into account; for example, the requirement for folate
of those carrying certain variants of the MTHFR gene
(around 10% of the population tested thus far) might,
arguably, need to be set higher than for the rest of the
population.
It is now recognized that there are several levels for
considering the concept of optimal nutrition, i.e., the
level that:
● prevents defi ciency symptoms, traditionally used to
establish reference nutrient intakes
● optimizes body stores of a nutrient
● optimizes some biochemical or physiological
function
● minimizes a risk factor for some chronic disease
● minimizes the incidence of a disease.
In the USA, the reference value for calcium is based
on optimizing bone calcium levels, which is a move
away from the traditional approach of focusing on
preventing defi ciency symptoms. An example of
attempts to set the reference standard for optimizing
a biochemical function is a level of folic acid that
would minimize the plasma levels of homocysteine, a
potential risk factor for cardiovascular disease. Another
might be the level of zinc to optimize cell-mediated
immunity. An example of a possible reference stan-
dard to optimize a risk factor for a disease is the level
of sodium that would minimize hypertension or the
level of n-3 polyunsaturated fatty acids (PUFAs) to
lower plasma triacylglycerols (TAGs). The amount of
folic acid to minimize the population burden of neural
tube defect would be an example of a reference value
to minimize the incidence of a disease. At present,
there is much debate as to the best approach to choos-
ing criteria for setting reference standards for minerals
and vitamins, and this is an area that is likely to con-
tinue to court controversy. An important point to note
in this respect is that, while minimizing frank defi -
ciency symptoms of micronutrients is an acute issue
in many developing countries, any evolution of our
concepts of desirable or optimal nutrient require-
ments must lead to a revision of the estimate of the
numbers of those with inadequate nutrition.7.3 Interpretation and uses of
dietary recommendationsWhen using dietary recommendations, several impor-
tant points need to be considered.
The nutrient levels recommended are per person
per day. However, in practice this will usually be
achieved as an average over a period of time (days,
weeks, or months) owing to daily fl uctuations in the
diet. As stated above, the setting of a range of dietary
recommendations should encourage appropriate
interpretation of dietary intake data, rather than the
inappropriate assumption that the value identifi ed to
meet the needs of practically all healthy people is a
minimum requirement for individuals. If an individ-
ual’s nutrient intake can be averaged over a suffi cient
period then this improves the validity of the compari-
son with dietary recommendations. However, in the
case of energy intakes, such a comparison is still inap-
propriate: dietary reference values for energy are
intended only for use with groups, and it is more