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.
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.
Flesh-formers, heat-givers, and bone-formers
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 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 (K2O). 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.
Soaking in cold water
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.
Carbon compounds or heat-producers
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 hydrohould 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.)
From acid and rancidity
The most esteemed and dearest oil is Almond. What h they are not as agreeable to English taste as the oil previousad 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.
The essential part of every living cell
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.
A comparatively small quantity of proteid matter, such as is easily obtained from vegetable food, is ample for the general needs of the body.
Flesh contains no starch or sugar, but a small quantity of glycogen. The fat in an animad have been sufficient evidence against the earlier view.
A comparison of flesh and vegetable food, shows in fble foods, particularly nuts, contain much fat.
Investigation of the digestive processes has shown that the carbohyd 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 propoums 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 macteriologist, Elie Metchnikoff, has given it as his opinion ns, to which the natives and the few of his own countrymen, living in accordance with natural laws are strangers.
Excerpt from: The Chemistry of Food and Nutrition by A. W. Duncan
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