However, before a study of any of these matters is entered into, it is
necessary to know just what is meant by food and what food does for the
body. As is well understood, the body requires material by which it may
be built and its tissues repaired when they are torn down by work and
exercise. In addition it requires a supply of heat to maintain it at
normal temperature and provide it with sufficient energy to do the work
required of it. The material that will accomplish these important things
is food, which may therefore be regarded as anything that, when taken
into the body, will build and repair its tissues or will furnish it with
the energy required to do its work.


FOOD SUBSTANCES

11. Although, as has just been stated, food may be considered as
anything that the human engine can make over into tissue or use in
living and working, not all foods are equally desirable any more than
all materials are equally good in the construction of a steam engine and
in the production of its working power. Those food substances which are
the most wholesome and healthful are the ones to be chosen, but proper
choice cannot be made unless the buyer knows of what the particular food
consists and what it is expected to do. To aid in the selection of food,
therefore, it is extremely necessary to become familiar with the five
substances, constituents, or principles of which foods are made up;
namely, water, mineral matter, or ash, protein, fat, and carbohydrate. A
knowledge of these will help also in determining the cooking methods to
adopt, for this depends on the effect that heat has on the various
substances present in a food. Of course, so far as flavor is concerned,
it is possible for the experienced cook to prepare many dishes
successfully without knowing the effect of heat on the different food