Introduction to Human Nutrition

7

Dietary Reference Standards

Kate M Younger

Key messages

• This chapter discusses the development of terminology and the
  change in conceptual approaches to setting nutrient recommen-
  dations from adequate to optimum nutrition.


• The interpretation and uses of dietary recommendations are
  discussed.


• The chapter describes how reference values can be used to assess
  the adequacy of the nutrient intakes of population groups.

© 2009 KM Younger.

• The methods used to determine requirements are discussed.
  These include deprivation studies, radioactive tracer studies,
  balance studies, factorial methods, measurement of nutrient
  levels in biological tissues, biochemical and biological markers,
  and animal experiments.

7.1 Introduction

The fi rst attempt to set standards for nutrient intakes
was by the Food and Nutrition Board of the National
Research Council of the USA in 1941, which pub-
lished recommended daily allowances (RDAs) in 1943
to “provide standards to serve as a goal for good
nutrition.” The fi rst UK RDAs followed in 1950, pub-
lished by the British Medical Association, and many
other countries and international agencies now
publish dietary standards that are intended to allow
the adequacy of the nutrient intakes of groups or
populations to be assessed by comparison with the
standards.
As the amount known about human requirements
and nutrient functions has increased, so too has the
size of the documents describing the recommenda-
tions, from a mere six pages dealing with 10 nutrients
in 1943 to the series of weighty books, each dealing
with the dietary reference intakes (DRIs) of only a few
of more than 30 nutrients, published by the Institute
of Medicine of the USA. Furthermore, continuing
research and the development of more informed
interpretations of the expanding body of data avail-
able necessitate the regular revision and updating of
the recommendations; thus, the “standards” of the

past become obsolete as they are replaced by new

fi gures based on new data or new interpretations of

existing data.

7.2 Terminology and conceptual

approaches to setting nutrient

recommendations

From the time of their fi rst issue in the 1940s and

throughout the next 50 years, the concepts and ter-

minology of RDAs remained unchanged. The basis on

which these RDAs were built was the statistical distri-

bution of individual requirements to prevent defi -

ciency criteria for the target nutrient. The peak of the

curve of the Gaussian distributions of such require-

ments is the “average requirement,” with half the

population having requirements above this value and

the other half having lower requirements. The RDA

was taken to be a point on that distribution that was

equal to the mean or “average requirements” plus 2

standard deviations (SDs) (Figure 7.1). By setting the

recommendation close to the upper end of the distri-

bution of individual requirements, the needs of most

of the population would be met. If the standard were

set to meet the apparent needs of almost everyone,

the resultant value would be so high as to be unat-