[Sidenote: Quantity of food required for various occupations]
The degree of energy required by the body depends very largely upon
the amount of work or activity it undergoes, hence the amount of food
required to supply this activity cannot be accurately prescribed
when the degree of required energy is unknown. However, there is a
certain amount of work performed by the beating of the heart and in
the maintenance of body-heat which can be fairly well estimated. The
quantity of energy-yielding food required, each twenty-four hours, for
the maintenance of the activities of life is about one vieno for every
ten pounds of body-weight. For a man at steady muscular work, such as
a carpenter or a farmer, this quantity should be about doubled. The
quantity required by a man of sedentary habits, but who takes regular
exercise for an hour or two each day, is about half way between these
two amounts. Thus, a man weighing one hundred forty pounds would require
one and one-half vienos for each ten pounds, or twenty-one vienos of
food each day. These weights apply only to people of normal flesh, who
desire neither to gain nor to lose.
The fact that either fat or carbohydrates can be used as a source of
muscular energy may be taken advantage of in prescribing dietaries
for persons whose digestive organs are so impaired that they cannot
digest a normal quantity of either of these nutrients, but who could
digest a small quantity of either. This does not mean, however,
that the proportion of fat and of carbohydrates in the food can be
disregarded. The digestive processes involved are radically different,
hence a suitable proportion of carbohydrates and fats should always be
maintained.
[Sidenote: Proportion of fat required under ordinary conditions]
With a view to guiding in a general way those who wish to adopt a
standard of diet for ordinary use, and who consult tables in which
fats and carbohydrates are listed separately, I might state that
the fat should form about one-eighth the total source of energy, or
one-sixteenth the weight of all water-free (solid) food eaten.
[Sidenote: Fallacy of lean meat producing muscle]
Until forty years ago the idea was held by scientists, and is still a
matter of popular belief, that nitrogenous foods are the sole source of
all muscular energy. This is quite a natural assumption. Lean meat is
muscle. If a man eats the muscle of another animal, by the primitive
process of reasoning, he should acquire muscle. This belief among people
who are not acquainted with physiological chemistry is almost universal,
while the facts are, the man who eats the muscle of an ox for the
purpose of adding strength to his own biceps is acting no more wisely
than the college boy who takes calf's brain for breakfast the day before
examination.
[Sidenote: Nitrogenous foods not a source of muscular energy]
The fact that nitrogenous foods are not a source of muscular energy has
been repeatedly proved by experiments on man and animals too numerous
to relate here. The sugar and the fat in the blood are taken into
the muscle-cells, and there unite with the oxygen brought from the
lungs, producing energy. When the body is fed upon proteids lacking a
sufficient quantity of other food elements, a portion of this proteid
is converted into glucose or sugar, which maintains body-heat and
energy. This is what happens in the case of carnivorous animals that
have excretory organs especially adapted to the converting and the
eliminating of useless or surplus products.
[Sidenote: Small amount of proteid matter required by animals]
It has been proved that dogs are capable of living for an indefinite
period of time upon a diet containing only a small proportion of
proteid matter, while maintaining health and increasing in weight.
Thus we see that even carnivorous animals require, for the maintenance
of the body-functions, a comparatively small amount of nitrogenous
material. Their strength and heat-forming elements can be secured
from carbohydrates and fats, probably to their actual benefit. It is
interesting to note, however, that dogs as a general rule cannot live
and thrive on a vegetable diet; a certain amount of animal proteids
seems indispensable. The same principle applies to other carnivorous
animals. Even ducks and chickens need a small percentage of animal
proteids in order to properly thrive and develop.
[Sidenote: Conditions governing quantity of nitrogen]
In order to maintain good health, every person requires a certain
amount of nitrogen, the quantity being governed by activity, exposure,
age, and temperature of environment. The growing youth needs nitrogen to
supply material for the tissue growth of his body; an emaciated person
who wishes to increase weight, a person recovering from illness, or a
man who is constantly performing strenuous work, would all require a
generous quantity of nitrogenous food.
[Sidenote: Lowest daily amount of nitrogen required]
The lowest possible nitrogen requirement for one of normal weight has
been determined by various methods to be from 40 to 60 decigrams per
day. This quantity, however, is the actual amount that is used in
the body-processes, and should be increased according to activity or
exposure to the open air.
[Sidenote: Amount of nitrogen required by the body]
From the results of numerous experiments under normal activity, the
quantity of nitrogenous food estimated to maintain the best bodily
condition is about three-fourths of a decigram for each pound of
body-weight; less than one-half of a decigram per pound of body-weight
would cause nitrogen starvation, while more than one decigram per pound,
except in the cases just mentioned, would result only in thrusting
needless work upon the liver and the kidneys, whose duties are to guard
the body against the results of incorrect eating. There are certain
conditions under which this amount of nitrogen may be exceeded in order
to gain definite and specific purposes, but in such cases the nature of
the proteid is of great importance. In certain occupations, for instance
sedative labor, the most soluble proteids, such as egg albumin (white of
eggs), milk, and green peas and beans should be selected; while in cases
of heavy manual labor, the heavier proteids, such as nuts, cheese, dried
legumes, fish and fowl should be selected.