By A.W. DUNCAN, F.C.S.
We may define a food to be any substance which will repair the functional
waste of the body, increase its growth, or maintain the heat, muscular,
and nervous energy. In its most comprehensive sense, the oxygen of the air
is a food; as although it is admitted by the lungs, it passes into the
blood, and there re-acts upon the other food which has passed through the
stomach. It is usual, however, to restrict the term food to such nutriment
as enters the body by the intestinal canal. Water is often spoken of as
being distinct from food, but for this there is no sufficient reason.
Many popular writers have divided foods into flesh-formers, heat-givers,
and bone-formers. Although attractive from its simplicity, this
classification will not bear criticism. Flesh-formers are also
heat-givers. Only a portion of the mineral matter goes to form bone.
Class I.--INORGANIC COMPOUNDS.
Sub-class 1. Water. 2. Mineral Matter or Salts.
Class II--ORGANIC COMPOUNDS.
1. Non-Nitrogeneous or Ternary Compounds. _a_ Carbohydrates.
_b_ Oils. _c_ Organic Acids.
2. Nitrogenous Compounds. _a_ Proteids. _b_ Osseids.
Class III.--NON-NUTRITIVES, FOOD ADJUNCTS AND DRUGS.
Essential Oils, Alkaloids, Extractives, Alcohol, &c.
These last are not strictly foods, if we keep to the definition already
given; but they are consumed with the true foods or nutrients, comprised
in the other two classes, and cannot well be excluded from consideration.
Water forms an essential part of all the tissues of the body. It is the
solvent and carrier of other substances.
Mineral Matter or Salts, is left as an ash when food is thoroughly
burnt. The most important salts are calcium phosphate, carbonate and
fluoride, sodium chloride, potassium phosphate and chloride, and compounds
of magnesium, iron and silicon.
Mineral matter is quite as necessary for plant as for animal life, and is
therefore present in all food, except in the case of some highly-prepared
ones, such as sugar, starch and oil. Children require a good proportion of
calcium phosphate for the growth of their bones, whilst adults require
less. The outer part of the grain of cereals is the richest in mineral
constituents, white flour and rice are deficient. Wheatmeal and oatmeal
are especially recommended for the quantity of phosphates and other salts
contained in them. Mineral matter is necessary not only for the bones but
for every tissue of the body.
When haricots are cooked, the liquid is often thrown away, and the beans
served nearly dry, or with parsley or other sauce. Not only is the food
less tasty but important saline constituents are lost. The author has made
the following experiments:--German whole lentils, Egyptian split red
lentils and medium haricot beans were soaked all night (16 hours) in just
sufficient cold water to keep them covered. The water was poured off and
evaporated, the residue heated in the steam-oven to perfect dryness and
weighed. After pouring off the water, the haricots were boiled in more
water until thoroughly cooked, the liquid being kept as low as possible.
The liquid was poured off as clear as possible, from the haricots,
evaporated and dried. The ash was taken in each case, and the alkalinity
of the water-soluble ash was calculated as potash (K_{2}O). The quantity
of water which could be poured off was with the German lentils, half as
much more than the original weight of the pulse; not quite as much could
be poured off the others.
G. Lentils. E. Lentils. Haricots. Cooked H.
Proportion of liquid 1.5 1.25 1.20 --
Soluble dry matter 0.97 3.38 1.43 7.66 per cent.
Ash 0.16 0.40 0.28 1.26 " "
Alkalinity as K_{2}O 0.02 0.082 0.084 0.21 " "
The loss on soaking in cold water, unless the water is preserved, is seen
to be considerable. The split lentils, having had the protecting skin
removed, lose most. In every case the ash contained a good deal of
phosphate and lime. Potatoes are rich in important potash salts; by
boiling a large quantity is lost, by steaming less and by baking in the
skins, scarcely any. The flavour is also much better after baking.
The usual addition of common salt (sodium-chloride) to boiled potatoes is
no proper substitute for the loss of their natural saline constituents.
Natural and properly cooked foods are so rich in sodium chloride and other
salts that the addition of common salt is unnecessary. An excess of the
latter excites thirst and spoils the natural flavour of the food. It is
the custom, especially in restaurants, to add a large quantity of salt to
pulse, savoury food, potatoes and soups. Bakers' brown bread is usually
very salt, and sometimes white is also. In some persons much salt causes
irritation of the skin, and the writer has knowledge of the salt food of
vegetarian restaurants causing or increasing dandruff. As a rule, fondness
for salt is an acquired taste, and after its discontinuance for a time,
food thus flavoured becomes unpalatable.
Organic Compounds are formed by living organisms (a few can also be
produced by chemical means). They are entirely decomposed by combustion.
The Non-Nitrogenous Organic Compounds are commonly called carbon
compounds or heat-producers, but these terms are also descriptive of the
nitrogenous compounds. These contain carbon, hydrogen and oxygen only, and
furnish by their oxidation or combustion in the body the necessary heat,
muscular and nervous energy. The final product of their combustion is
water and carbon dioxide (carbonic acid gas).
The Carbohydrates comprise starch, sugar, gum, mucilage, pectose,
glycogen, &c.; cellulose and woody fibre are carbohydrates, but are little
capable of digestion. They contain hydrogen and oxygen in the proportion
to form water, the carbon alone being available to produce heat by
combustion. Starch is the most widely distributed food. It is insoluble in
water, but when cooked is readily digested and absorbed by the body.
Starch is readily converted into sugar, whether in plants or animals,
during digestion. There are many kinds of sugar, such as grape, cane and
milk sugars.
The Oils and Fats consist of the same elements as the carbohydrates,
but the hydrogen is in larger quantity than is necessary to form water,
and this surplus is available for the production of energy. During their
combustion in the body they produce nearly two-and-a-quarter times (4 :
8.9 = 2.225) as much heat as the carbohydrates; but if eaten in more than
small quantities, they are not easily digested, a portion passing away by
the intestines. The fat in the body is not solely dependent upon the
quantity consumed as food, as an animal may become quite fat on food
containing none. A moderate quantity favours digestion and the bodily
health. In cold weather more should be taken. In the Arctic regions the
Esquimaux consume enormous quantities. Nuts are generally rich in oil.
Oatmeal contains more than any of the other cereals (27 analyses gave from
8 to 12.3 per cent.)
The most esteemed and dearest oil is Almond. What is called Peach-kernel
oil (Oleum Amygdalæ Persicæ), but which in commerce includes the oil
obtained from plum and apricot stones, is almost as tasteless and useful,
whilst it is considerably cheaper. It is a very agreeable and useful food.
It is often added to, as an adulterant, or substituted for the true Almond
oil. The best qualities of Olive oil are much esteemed, though they are
not as agreeable to English taste as the oil previously mentioned. The
best qualities are termed Virgin, Extra Sublime and Sublime. Any that has
been exposed for more than a short time to the light and heat of a shop
window should be rejected, as the flavour is affected. It should be kept
in a cool place. Not only does it vary much in freedom from acid and
rancidity, but is frequently adulterated. Two other cheaper oils deserve
mention. The "cold-drawn" Arachis oil (pea-nut or earth-nut oil) has a
pleasant flavour, resembling that of kidney beans. The "cold-drawn" Sesamé
oil has an agreeable taste, and is considered equal to Olive oil for
edible purposes. The best qualities are rather difficult to obtain; those
usually sold being much inferior to Peach-kernel and Olive oils.
Cotton-seed oil is the cheapest of the edible ones. Salad oil, not sold
under any descriptive name, is usually refined Cotton-seed oil, with
perhaps a little Olive oil to impart a richer flavour.
The solid fats sold as butter and lard substitutes, consist of deodorised
cocoanut oil, and they are excellent for cooking purposes. It is claimed
that biscuits, &c., made from them may be kept for a much longer period,
without showing any trace of rancidity, than if butter or lard had been
used. They are also to be had agreeably flavoured by admixture with
almond, walnut, &c., "cream."
The better quality oils are quite as wholesome as the best fresh butter,
and better than most butter as sold. Bread can be dipped into the oil, or
a little solid vegetable fat spread on it. The author prefers to pour a
little Peach-kernel oil upon some ground walnut kernels (or other ground
nuts in themselves rich in oil), mix with a knife to a suitable
consistency and spread upon the bread. Pine-kernels are very oily, and can
be used in pastry in the place of butter or lard.
Whenever oils are mentioned, without a prefix, the fixed or fatty oils are
always understood. The volatile or essential oils are a distinct class.
Occasionally, the fixed oils are called hydrocarbons, but hydrocarbon
oils are quite different and consist of carbon and hydrogen alone. Of
these, petroleum is incapable of digestion, whilst others are poisonous.
Vegetable Acids are composed of the same three elements and undergo
combustion into the same compounds as the carbohydrates. They rouse the
appetite, stimulate digestion, and finally form carbonates in combination
with the alkalies, thus increasing the alkalinity of the blood. The chief
vegetable acids are: malic acid, in the apple, pear, cherry, &c.; citric
acid, in the lemon, lime, orange, gooseberry, cranberry, strawberry,
raspberry, &c.; tartaric acid, in the grape, pineapple, &c.
Some place these under Class III. or food adjuncts. Oxalic acid (except
when in the insoluble state of calcium oxalate), and several other acids
are poisonous.
Proteids or Albuminoids are frequently termed flesh-formers. They are
composed of nitrogen, carbon, hydrogen, oxygen, and a small quantity of
sulphur, and are extremely complex bodies. Their chief function is to form
flesh in the body; but without previously forming it, they may be
transformed into fat or merely give rise to heat. They form the essential
part of every living cell.
Proteids are excreted from the body as water, carbon dioxide, urea, uric
acid, sulphates, &c.
The principal proteids of animal origin have their corresponding proteids
in the vegetable kingdom. Some kinds, whether of animal or vegetable
origin, are more easily digested than others. They have the same
physiological value from whichever kingdom they are derived.
The Osseids comprise ossein, gelatin, cartilage, &c., from bone, skin,
and connective issue. They approach the proteids in composition, but
unlike them they cannot form flesh or fulfil the same purpose in
nutrition. Some food chemists wish to call the osseids, albuminoids; what
were formerly termed albuminoids to be always spoken of as proteids only.
Jellies are of little use as food; not only is this because of the low
nutritive value of gelatin, but also on account of the small quantity
which is mixed with a large proportion of water.
The Vegetable Kingdom is the prime source of all organic food; water,
and to a slight extent salts, form the only food that animals can derive
directly from the inorganic kingdom. When man consumes animal food--a
sheep for example--he is only consuming a portion of the food which that
sheep obtained from grass, clover, turnips, &c. All the proteids of the
flesh once existed as proteids in the vegetables; some in exactly the same
chemical form.
Flesh contains no starch or sugar, but a small quantity of glycogen. The
fat in an animal is derived from the carbohydrates, the fats and the
proteids of the vegetables consumed. The soil that produced the herbage,
grain and roots consumed by cattle, in most cases could have produced food
capable of direct utilisation by man. By passing the product of the soil
through animals there is an enormous economic loss, as the greater part of
that food is dissipated in maintaining the life and growth; little remains
as flesh when the animal is delivered into the hands of the butcher. Some
imagine that flesh food is more easily converted into flesh and blood in
our bodies and is consequently more valuable than similar constituents in
vegetables, but such is not the case. Fat, whether from flesh or from
vegetables is digested in the same manner. The proteids of flesh, like
those of vegetables, are converted into peptone by the digestive
juices--taking the form of a perfectly diffusible liquid--otherwise they
could not be absorbed and utilised by the body. Thus the products of
digestion of both animal and vegetable proteids and fats are the same.
Formerly, proteid matter was looked upon as the most valuable part of the
food, and a large proportion was thought necessary for hard work. It was
thought to be required, not only for the construction of the muscle
substance, but to be utilised in proportion to muscular exertion. These
views are now known to be wrong. A comparatively small quantity of proteid
matter, such as is easily obtained from vegetable food, is ample for the
general needs of the body. Increased muscular exertion requires but a
slight increase of this food constituent. It is the carbohydrates, or
carbohydrates and fats that should be eaten in larger quantity, as these
are the main source of muscular energy. The fact that animals, capable of
the most prolonged and powerful exertion, thrive on vegetables of
comparatively low proteid value, and that millions of the strongest races
have subsisted on what most Englishmen would consider a meagre vegetarian
diet, should have been sufficient evidence against the earlier view.
A comparison of flesh and vegetable food, shows in flesh an excessive
quantity of proteid matter, a very small quantity of glycogen (the animal
equivalent of starch and sugar) and a variable quantity of fat. Vegetable
food differs much, but as a rule it contains a much smaller quantity of
proteid matter, a large proportion of starch and sugar and a small
quantity of fat. Some vegetable foods, particularly nuts, contain much
fat.
Investigation of the digestive processes has shown that the carbohydrates
and fats entail little strain on the system; their ultimate products are
water and carbon dioxide, which are easily disposed of. The changes which
the proteids undergo in the body are very complicated. There is ample
provision in the body for their digestion, metabolism, and final
rejection, when taken in moderate quantity, as is the case in a dietary of
vegetables. The proteids in the human body, after fulfilling their
purpose, are in part expelled in the same way as the carbohydrates; but
the principal part, including all the nitrogen, is expelled by the kidneys
in the form of urea (a very soluble substance), and a small quantity of
uric acid in the form of quadurates.
There is reciprocity between the teeth and digestive organs of animals and
their natural food. The grasses, leaves, &c., which are consumed by the
herbivora, contain a large proportion of cellulose and woody tissue.
Consequently, the food is bulky; it is but slowly disintegrated and the
nutritious matter liberated and digested. The cellulose appears but
slightly acted upon by the digestive juices. The herbivora possess
capacious stomachs and the intestines are very long. The carnivora have
simpler digestive organs and short intestines. Even they consume
substances which leave much indigestible residue, such as skin, ligaments
and bones, but civilised man, when living on a flesh dietary removes as
much of such things as possible. The monkeys, apes, and man (comprised in
the order _Primates_) have a digestive canal intermediate in complexity
and in length to the herbivora and carnivora. A certain quantity of
indigestible matter is necessary for exciting peristaltic action of the
bowels. The carnivora with their short intestinal canal need the least,
the frugivora more, and the herbivora a much larger quantity. The
consumption by man of what is commonly called concentrated food is the
cause of the constipation to which flesh-eating nations are subject. Most
of the pills and other nostrums which are used in enormous quantities
contain aloes or other drugs which stimulate the action of the intestines.
Highly manufactured foods, from which as much as possible of the
non-nutritious matter has been removed is often advocated, generally by
those interested in its sale. Such food would be advantageous only if it
were possible to remove or modify a great part of our digestive canal (we
are omitting from consideration certain diseased conditions, when such
foods may be useful). The eminent physiologist and bacteriologist, Elie
Metchnikoff, has given it as his opinion that much of man's digestive
organs is not only useless but often productive of derangement and
disease. In several cases where it has been necessary, in consequence of
serious disease, to remove the entire stomach or a large part of the
intestines, the digestive functions have been perfectly performed. It is
not that our organs are at fault, but our habits of life differ from that
of our progenitors. In past times, when a simple dietary in which flesh
food formed little or no part, and to-day, in those countries where one
wholly or nearly all derived from vegetable sources and simply prepared is
the rule, diseases of the digestive organs are rare. The Englishman going
to a tropical country and partaking largely of flesh and alcohol, suffers
from disease of the liver and other organs, to which the natives and the
few of his own countrymen, living in accordance with natural laws are
strangers.
Indigestible Matter--Food is never entirely digested. As a reason
against confining ourselves solely to vegetable food, it has been stated
that such is less perfectly digested than animal food and that it
therefore throws more work on the digestive organs. It is also urged that
on this account a greater quantity of vegetable food is required. We have
shown elsewhere that, on the contrary, vegetarians are satisfied with a
smaller amount of food. Man requires a small quantity of woody fibre or
cellulose in his food to stimulate intestinal action and prevent
constipation.
It is difficult to determine how much of a food is unassimilated in the
body. This is for the reason of the intestinal refuse consisting not only
of undigested food, but also of residues of the digestive juices, mucus
and epithelial debris. These latter have been shown to amount to from
one-third to one-half of the whole of the fæces, which is much more than
had previously been supposed.
John Goodfellow has shown that of very coarse wholemeal bread quite 14 per
cent. was undigested, whilst bread made from ordinary grade wholemeal
showed 12.5 per cent. Such a method of analysis was adopted as it was
believed would exclude other than the food waste. The experiments were
made on a person who was eating nothing but the bread. It seems probable
that a smaller proportion would have remained unassimilated had the bread
not formed the sole food. It is advisable that wheatmeal he ground as
finely as possible, the coarse is not only to a less extent assimilated
but apt to irritate the bowels. Notwithstanding that fine white bread gave
only 4.2 per cent. and a coarse white bread 4.9 per cent. of waste, a fine
wheatmeal bread is more economical as the same quantity of wheat produces
a greater weight of flour richer in proteid and mineral matter. From a
large number of experiments with man, it has been calculated that of
proteids there is digested when animal food is eaten 98 per cent., from
cereals and sugars 8 per cent., from vegetables and fruits 80 per cent.
The difference between the proportions digested of the other food
constituents was much less. Although there is here a theoretical advantage
in favour of animal food, there are other considerations of far more
importance than a little undigestible waste. The main question is one of
health. In some dietary experiments of a girl aged 7, living upon a fruit
diet, of whom we have given some particulars elsewhere, Professor Jaffa
gives the following particulars. During the ten days trial the percentages
absorbed were proteids 82.5, fat 86.9, nitrogen free extract 96, crude
fibre 80, ash 5.7, heat of combustion in calories 86.7. He says,
"generally speaking, the food was quite thoroughly assimilated, the
coefficients of digestibility being about the same as are found in an
ordinary mixed diet. It is interesting to note that 80 per cent. of the
crude fibre appeared to be digested. The results of a number of foreign
experiments on the digestibility of crude fibre by man are from 30 to 91.4
per cent., the former value being from mixed wheat and rye, and the latter
in a diet made of rice, vegetables and meat."