Introduction to Human Nutrition

Dietary Reference Standards 127

and has responded by providing foods to address
particular perceived needs, and more informative
food labels.
● Researchers and the health professions need to
assess the nutritional adequacy of the diets of
groups (or, cautiously, of individuals) by compar-
ing dietary intake survey data with the dietary refer-
ence values (see below). Once the limitations of the
dietary assessment data have been taken into
account (see Chapter 10), this information can be
used to attempt to improve people’s nutrient intakes
by bringing them more into line with the dietary
recommendations. The formulation of dietary
advice or guidelines depends on an appreciation of
the existing situation: the solution can only be
framed once the problem is characterized.
● Institutions and caterers use dietary recommenda-
tions to assess the requirements of groups and
devise nutritionally adequate menus. This is a great
deal more easily said than done, mainly because of
the fi nancial constraints involved and, often, the
food preferences of the population being catered
for.
● The public needs this information to help in the
interpretation of nutrition information on food
labels that may describe nutrient content in both
absolute terms (g, mg, etc.) and as a percentage of
the recommended dietary allowance (RDA) for that
nutrient (usually per 100 g or per “serving”). It is
thought that the latter is more meaningful to con-
sumers, even though the concepts involved in
setting the dietary recommendations are rather
complex (making it diffi cult to judge which level of
recommendation should be used as the standard)
and they can be open to misinterpretation (see
above). Since 1998, some UK manufacturers and
retailers have provided information about guide-
line daily amounts (GDAs) for energy, some nutri-
ents, salt, and fi ber. These were developed by the
Institute of Grocery Distribution (IGD, a UK
research and training body for the food and grocery
chain) and are derived from the DRVs [and the
British Committee on Medical Aspects of Food
Policy (COMA) and Scientifi c Advisory Council
on Nutrition (SACN) recommendations for salt
intake], but are much simplifi ed. Unless consumers
are provided with nutrition information in the
most appropriate form on food labels, they cannot
make informed choices as to what foods to buy and

eat to meet their own perceived needs. At the very

least, consumers should be able to compare prod-

ucts to get their money’s worth.

7.4 The use of reference values to assess

the adequacy of the nutrient intakes of

population groups

Ideally, this is accomplished by discovering the distri-

bution of intakes of a nutrient in the population

group (e.g., by carrying out a dietary survey), and

comparing these intakes with the distribution of

requirements for that nutrient within the same popu-

lation. In practice, reliable data with which to plot the

second of these distributions have rarely been col-

lected, and therefore what must be used is an estima-

tion of the average requirement together with an esti-

mation of the variance in that requirement, i.e., the

standard deviation (based on whatever scientifi c evi-

dence is available), that is used to plot the population

distribution of requirements as shown in Figure 7.1.

When considering how to assess the adequacy of

nutrient intakes of populations it is important

to compare the intakes with the most appropriate

level of requirement as defi ned in dietary

recommendations.

It is not useful to compare usual intakes with the

RDA (PRI, RNI, i.e., the average requirement plus a

notional 2 SDs) at the population level since this

approach leads to overestimates of the prevalence of

inadequacy. (It may, however, be justifi ed to compare

an individual’s intake with the RDA.) Furthermore,

this approach might be seen to encourage the con-

sumption of higher intakes, which could be toxic in

the case of certain nutrients.

Comparison of the population intake with the

average requirement [AR; estimated average require-

ment (EAR)] is now considered to be the best estima-

tion of dietary adequacy; if the average intake is less

than the average requirement, then it is clear that

there could be a problem in that population. Accord-

ingly, using the average requirement as a cut-off point,

the proportion of individuals in the group whose

usual intakes are not meeting their requirements can

be calculated, allowing the problem to be quantifi ed.

However, this approach cannot be used in the case of

energy since energy intakes and requirements are

highly correlated (the effects of an imbalance being

quickly obvious to the individual).