foods are composed. It is concerned with the amounts of these nutrients which are required for
the proper growth and functioning of the body, the way in which each one is useful to the body,
and what happens when there is too little or too much of one or other component in a person's
diet. Nutrition is a quantitative science; that is to say, it is a study of the amount of each nutrient
required by an individual. It is not sufficient to know that protein, for example is a necessary
constituent of the diet; we must know the amount required as well, for sometimes it is as
harmful to eat too much of a nutrient as too little. Nutritional science therefore deals both with
the amounts of each nutrient necessary for the proper functioning of the body and also with the
amounts contributed by different kinds of food.
Although the function and the required amount of each nutrient must be taken into account, it
is also important to recognize that there may be quite wide variations between the quantities
needed by different individuals. The human species is uniform to some degree and the
nutritional requirements of men or women, old people or children, can be assessed within
certain limits of precision. Nevertheless, general statements concerning needs-for example, that
'children require a daily pint of milk or that a glass of orange juice each day is necessary for
health' –are not expressions of scientific truth, even if the contents of protein and calcium in the
milk and vitamin C in t6he orange juice are expressed and interpreted in scientific terms.
Two further points must also be remembered in studing nutrition. The first is that all science is
merely the minimising of doubt. Our knowledge of nutrition has justified itself by the degree of
command which has enabled us to achieve over events by which, indeed, the correctness of our
scientific knowledge has been verified. Understanding of the chemical structure of vitamin D,
first elucidated in 1932, soon led to the prevention of rickets, the bone disease of children.
Nevertheless, our understanding of the chemistry of vitamin D – active substances in the diet and
as they occur in the body is still developing. Our nutritional knowledge is now considerable but,
as always in science, there is certainly more to know.
Finally, it must always be remembered that success in nutrition can only be recognized in
health, and the concept of health is a complicated one. Nutrition is in some respects a branch of
chemical science or, more exactly, of biochemistry – that is, the chemistry of life; but it is more
than this. Children cannot grow properly unless they are given the right food to eat; this is a part
of the science of nutrition. But there is now good scientific evidence to show that children and
young animals grow better if they are given attention and love as well as vitamins and proteins.
An expert committee of the World Health Organizasion has defined health, towards which good
nutrition is intended to contribute, as 'complete physical, mental, and social well-being and not
the mere absence of ill-health and infirmity'. This definition comprises a great deal. Its lesson to
the students of nutrition is, however, that although nutritional science is an important and
rewarding area of study, the nutritionist must always remember that man does not live by bread