There are various elements found in food.
Those elements are starch, sugar, fats, albumen, mineral substances, and indigestible
substances.
Based on their chemical composition, the
digestible food elements are often grouped into three classes: carbonaceous,
nitrogenous, and inorganic. The carbonaceous class includes starch, sugar, and
fats; the nitrogenous, all albuminous elements, and the inorganic comprises the
mineral elements.
Starch is only found in vegetable foods. All
grains, most vegetables, and some fruits, contain starch in abundance. Several
kinds of sugar are made in nature's laboratory; cane, grape, fruit, and milk
sugar. The first is obtained from the sugar-cane, the sap of maple trees, and
from the beet root. Grape and fruit sugars are found in most fruits and in
honey. Milk sugar is one of the constituents of milk. Glucose, an artificial
sugar resembling grape sugar, is now largely manufactured by subjecting the
starch of corn or potatoes to a chemical process; but it lacks the sweetness of
natural sugars, and is by no means a proper substitute for them. Albumen is
found in its purest, uncombined state in the white of an egg, which is almost
wholly composed of albumen. It exists, combined with other food elements, in
many other foods, both animal and vegetable. It is found abundant in oatmeal,
and to some extent in the other grains, and in the juices of vegetables. All
natural foods contain elements which in many respects resemble albumen, and are
so closely allied to it that for convenience they are usually classified under
the general name of "albumen." The chief of these is gluten, which is
found in wheat, rye, and barley. Casein, found in peas, beans, and milk, and
the fibrin of flesh, are elements of this class.
Fats are found in both animal and vegetable
foods. Of animal fats, butter and suet are common examples. In vegetable form,
fat is abundant in nuts, peas, beans, in various of the grains, and in a few
fruits, as the olive. As furnished by nature in nuts, legumes, grains, fruits,
and milk, this element is always found in a state of fine subdivision, which
condition is the one best adapted to its digestion. As most commonly used, in
the form of free fats, as butter, lard, etc., it is not only difficult of
digestion itself, but often interferes with the digestion of the other food
elements which are mixed with it. It was doubtless never intended that fats
should be so modified from their natural condition and separated from other
food elements as to be used as a separate article of food. The same may be said
of the other carbonaceous elements, sugar and starch, neither of which, when
used alone, is capable of sustaining life, although when combined in a proper
and natural manner with other food elements, they perform a most important part
in the nutrition of the body. Most foods contain a percentage of the mineral
elements. Grains and milk furnish these elements in abundance. The cellulose,
or woody tissue, of vegetables, and the bran of wheat, are examples of
indigestible elements, which although they cannot be converted into blood in
tissue, serve an important purpose by giving bulk to the food.
With the exception of gluten, none of the
food elements, when used alone, are capable of supporting life. A true food
substance contains some of all the food elements, the amount of each varying in
different foods.