Hot Weather]

Generally the quantity of food should be slightly decreased in hot
weather, when fewer calories are needed to sustain the heat of the body.
In particular, less meat should be eaten in the summer, on account of
what is called the "specific dynamic action of protein," that is, the
special tendency of meats and like foods to produce immediate heat.

Each individual must decide for himself what is the right amount of food
to eat. In general, that amount is right which will maintain the most
favorable condition of weight. If the weight, endurance, and general
feeling of well-being are maintained, one may assume that sufficient
food is taken.

[Sidenote: Brainwork and Eating]

It is physical, not mental work, which uses up the greater part of our
food. The common impression that brain-work or expenditure of mental
energy creates a special need for food is erroneous. The sedentary
brain-worker often gains weight without eating very much. What he really
needs is exercise, to use up the food, but if he will not take
exercise, then he should reduce his food even below the small amount on
which he gains weight.

[Sidenote: Eating When Fatigued]

Which meal in the day should be heavy and which light depends largely on
one's daily program of work, the aim being to avoid heavy meals just
before heavy work. When very tired it is sometimes advisable to skip a
meal or to eat only lightly, as of fruits and salads. A man who eats
heartily when he is very tired is likely to be troubled afterward with
indigestion.

(See SUPPLEMENTARY NOTES for specific directions regarding diet for
underweight and overweight.)

Section II--Protein Foods

[Sidenote: Protein, Fat, and Carbohydrate]

In the last section it was stated that food is fuel. But there is one
constituent of food which, while it _can_ be used as fuel, is especially
fitted for an entirely different purpose, namely, to build tissue, that
is, to serve for the growth and repair of the body. This tissue-building
constituent in food is called protein. The two other chief constituents
in food are fat and carbohydrate, the last term embracing what are
familiarly known as starch and sugar. Fats and carbohydrates are only
for fuel and contain carbon as the essential element. Protein contains
nitrogen as the essential element in tissue-building. The white of egg
and the lean of meat afford the most familiar examples of protein. They
consist entirely of protein and wa