Food Classification.
The following are familiar examples of compounds of each of the four
principal classes of nutrients:
PROTEIN:
_Proteids._
_Albuminoids_, _e.g._, albumen of eggs; myosin,
the basis of muscle (lean meat); the albuminoids
which make up the gluten of wheat, etc.
_Gelatinoids_, constituents of connective tissue which
yield gelatin and allied substances, _e.g._, collagen
of tendon; ossein of bone.
"Nitrogenous extractives" of flesh, _i.e._, of meats and fish.
These include kreatin and allied compounds, and are the
chief ingredients of beef tea and most meat extracts.
Amids: this term is frequently applied to the nitrogenous
non-albuminoid compounds of vegetable foods and feeding
stuffs, among which are amido acids, such as aspartic acid
and asparagin. Some of them are more or less allied in
chemical constitution to the nitrogenous extractives of
flesh.
_Fats._
Fat of meat: fat of milk; oil of corn, wheat, etc. The
ingredients of the "ether extract" of animal and vegetable
foods and feeding stuffs, which it is customary to group
together roughly as fats, include, with the true fats,
various other substances, as lecithians, and chlorophylls.
_Carbohydrates_, sugars, starches, celluloses, gums, woody fibre, etc.
_Mineral matter._
Potassium, sodium, calcium and magnesium chlorids, sulphates
and phosphates. (Atwater).
The terms (_a_) "nitrogenous" and (_b_) "carbonaceous" are frequently
used to designate the two distinct classes of food, viz.: (_a_) the
tissue builders and flesh formers; (_b_) fuel and force producers.
Each of these classes contains food material derived from both the
animal and vegetable kingdom, although the majority of the animal
substances belong to the nitrogenous, and the majority of the
vegetable substances to the carbonaceous group.
Therefore, for practical purposes, we will confine ourselves to the
more general terms used in Atwater's table.
Uses of Food.
First, food is used to form the materials of the body and repair its
waste; second, to yield energy in the form of (1) heat to keep the
body warm, (2) to provide muscular and other power for the work it has
to do. In forming the tissues and fluids of the body the food serves
for building and repair. In yielding energy, it serves as fuel for
heat and power. The principal tissue formers are the albuminoids;
these form the frame-work of the body. They build and repair the
nitrogenous materials, as those of muscle, tendon and bone, and supply
the albuminoids of blood, milk and other fluids. The chief fuel
ingredients of food are the carbohydrates and fats. These are either
consumed in the body or are stored as fat to be used as occasion
demands.
Water.
By referring to a preceding chapter we find that water composes
three-fifths of the entire body. The elasticity of muscles, cartilage,
tendons, and even of bones is due in great part to the water which
these tissues contain. The amount of water required by a healthy man
in twenty-four hours (children in proportion) is on the average
between 50 and 60 ounces, beside about 25 ounces taken as an
ingredient of solid food, thus making a total of from 75 to 85 ounces.
One of the most universal dietetic failings is neglect to take enough
water into the system. Dr. Gilman Thompson gives the following uses of
water in the body:--
(1) It enters into the chemical composition of the tissues; (2) it
forms the chief ingredient of all the fluids of the body and maintains
their proper degree of dilution; (3) by moistening various surfaces of
the body, such as the mucous and serous membranes, it prevents
friction and the uncomfortable symptoms which might result from
drying; (4) it furnishes in the blood and lymph a fluid medium by
which food may be taken to remote parts of the body and the waste
matter removed, thus promoting rapid tissue changes; (5) it serves as
a distributer of body heat; (6) it regulates the body temperature by
the physical processes of absorption and evaporation.
Salts (Mineral Matter).--Use of Salts in Food.
(1) To regulate the specific gravity of the blood and other fluids of
the body; (2) to preserve the tissues from disorganization and
putrefaction; (3) to enter into the composition of the teeth and
bones. These are only a few of the uses of salts in the body, but are
sufficient for our purpose. Fruits and nuts contain the least quantity
of salts, meat ranks next, then vegetables and pulses, cereals contain
most of all (Chambers). Sodium chloride (common salt) is the most
important and valuable salt. It must not however be used in excess.
Potassium salts rank next in importance.[4] Calcium, phosphorus,
sulphur and iron are included in this class.
The quantity of salts or mineral matter contained in some important
articles of vegetable and animal food is shown in this table (Church):
_Mineral Matter in 1,000 lbs. of 14 Vegetable Products._
Lbs.
Apples 4
Rice 5
Wheaten flour 7
Turnips 8
Potatoes 10
Barley 11
Cabbage 12
Bread 12
Watercress 13
Maize 20
Oatmeal 21
Peas 30
Cocoa nibs 36
Wheaten bran 60
_Mineral Matter in 1,000 lbs. of 8 Animal Products._
Lbs.
Fat Pork 5
Cow's milk 7
Eggs (without shells) 13
Lean of mutton 17
Flesh of common fowl 16
Bacon 44
Gloucester cheese 49
Salted herrings 158
"In most seeds and fruits there is much phosphate in the mineral
matter, and in most green vegetables much potash. One important kind
of mineral matter alone is deficient in vegetable food, and that is
common salt."
FOOTNOTE:
[4] See Vegetables, Chap. VII.