o burn as fuel for all the activities of
the body, just as any other machine needs fuel. The fuel value of
food, or its energy, is measured in _calories_. A calorie measures the
amount of heat or energy given off when anything burns, whether it is
coal in a stove or food in the body.

Practically all foods give this fuel or energy, but some give much
more than others. Fats give more fuel than an equal weight of any
other food. Sugar and foods rich in starch like flour and corn meal
are fuel foods. This is one of the reasons why they are chosen to be
shipped abroad. The cereals always supply an important part of the
fuel of the diet. Watery foods, like many vegetables and fruits,
normally give less fuel. A person could not live on lettuce any better
than a house could be heated with tissue paper.

If the food does not supply enough energy, a person will burn up
part of his own body for fuel and will grow emaciated. Far too often
we find children of the very poor who are undernourished because of
lack of food fuel. Sometimes even well-to-do young people half starve
themselves because they get "notions" about food. One of the terrible
tragedies abroad is the hundreds and thousands of men and women and
children who are worn and thin and sick for lack of food.

We need food, too, to keep the organs of the body running smoothly.
Abroad, people are suffering not only because they have not enough
food, but because they have not the right kinds of food. Milk and
vegetables and fruits are especially useful. They are the chief
sources of the much-needed _mineral salts_ and the two _vitamines_.
The vitamines are substances of great importance about which has
centred much discussion lately and which scientists do not yet fully
understand, though they realize that they are essential for the growth
of children and for health in adults.

The _protein_ of food is used to build the body if we are young, and
to restore the daily wear and tear if we are older. The mineral salts
are also necessary for this purpose. Protein will be discussed further
in the chapter on meat and meat substitutes, but it should be realized
here that the protein we eat comes not only from these foods, but also
from the cereals. Cereals supply a full half of the protein of many
diets.

Cereals are therefore important for their fuel since they are rich in
starch, and for their protein, and, if we eat the entire kernel, for
their mineral matter and vitamines.