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Chapter IV-—Elementary principles of Nutrition

Food Values and Food Requirements.

A brief statement on the nutritive value of different foods and
on the special requirements of different classes of individuals
may be helpful as a guide to catering.

In order to maintain a proper state of nutrition the diet must
contain sufficient of all the nutritive factors (nutrients) which the
body requires. There are three classes of these, namely, energy-
giving, constructive and protective.

Energy-giving foods supply the body with the materials which'
it needs to produce heat, muscular work and to keep going the
basic activities of life, such as the heart beat and respiration.

The constructive foods are those which are rich in the nutrients
out of which the body is constructed. The predominant material
composing the soft parts of the body—the muscles, brain, liver,
intestines, etc., is protein, a substance of complex structure
whose essential element is nitrogen. Every food rich in protein
therefore belongs to the constructive class. The essential
materials of the bony framework of the body and of the teeth
are calcium, phosphates and magnesium. Other minerals such
as iron also enter into the structure of the body. Foods which
are rich in these elements are also constructive.

It is difficult to state concisely the functions of the protective
foods. The recognition of the roles played in the body by the
protective nutrients constitutes the main achievements of the
science of nutrition during the past quarter of a century, and
these ate being added to and new relationships are being
brought to light from time to time. A complete and satisfactory
definition of the protective foods will therefore have to await
the time when knowledge has become more stabilised. In the
most general terms, the protective foods may be said to provide
the lubricating material which facilitates the orderly operation
of the machinery of the body, thus enabling the body to develop
and function in all its parts in a smooth and orderly fashion.
This means good health and good development. The term
" protective " arose from the fact that disorganised growth
and bodily function and actual disease were found to result
from deficiency of the protective factors in the diet. These are,
so far as is known at present, the mineral elements and the
vitamins, and all foods which contain relatively large amounts
of these nutrients are known as " protective ".

With few exceptions, all foods are in some measure energy-
giving, constructive and protective. For example, milk is not
only the best of all constructive foods, it is in addition the best
in the protective class and is a good source of energy. In the
classifications which follow a number of foods will therefore be
found in more than one class.   The most notable exceptions to