This is the name given to certain organic compounds of carbon that are produced by plants in the process of growth from carbon, hydrogen and oxygen, with the oxygen and hydrogen in proportions to form water. In everyday language we know the most important of these carbohydrates as starches and sugars. As will be seen later, carbohydrates are complex substances composed, in most instances, of simpler substances, or building blocks, called sugars. Chief among the carbohydrates are:
Nuts--A few varieties--acorns, chestnuts and cocoanuts.
Tubers--potatoes, sweet potatoes, carrots, artichokes, parsnips, etc.
Legumes--Most beans, except some varieties of soybeans, all peas, peanuts.
Cereals--All grains and practically all cereal products. (Gluten bread is not a carbohydrate.)
The reader will notice that grains and legumes are classed both as proteins and carbohydrates. This is due to the fact that they contain enough of each of these food elements to be placed in both classes. Nuts, for the same reason, are classed both as proteins and as fats. Milk, commonly classed as a protein is really low in protein. It may with equal justification be classed as a sugar or carbohydrate. All foods contain more or less carbohydrates, as they all contain more or less protein. Most foods contain some fats, but there is none in most fruits nor in the green leaves of vegetables.
Carbohydrates, like proteins, are composed of simpler compounds known as simple sugars or monosaccharides. According to their composition, these are classed as follows:
1. Monosaccharides: Sugars containing only one sugar group or radical. Among the monosaccharides are grape sugar (glucose or dextrose), fruit sugar (fructose or levulose), and galactose of honey. These are the assimilable forms of carbohydrate. Dextrose is the principle member of the glucose group and much less sweet than cane sugar. It is known as grape sugar and is found in fruits, some vegetables and honey. Glucose occurs in both plants and animals and is formed by the action of heat and the ultraviolet rays upon starch in the presence of an acid. Corn syrup is commercially known as glucose. Glucose may also be made by treating starch with sulphuric acid in the presence of heat. Fructose and levulose are derived from fruits and honey. Galactose is a crystaline glucose obtained by treating milk sugar with dilute acids.
2. Disaccharides: Sugars containing two simple sugars, or that can be broken into two monosaccharides. The ordinary cane sugar or sucrose of commerce is a disaccharide composed of glucose and galactose. Invert sugar found in honey is a mixture of glucose and fructose. Maltose or malt sugar is composed of galactose and glucose. Maple sugar (sucrose) and milk sugar (lactose) are also disaccharides.
3. Trisaccharides: Sugars containing three sugar groups or radicals. Beet sugar is the best known example of this sugar.
4. Polysaccharides: Colloids or non-crystalizable organic substances known as starches. There are three main groups of polysaccharides: 1. Starches; 2. glycogen (animal starch), and 3. pentosans. Pentosans are numerous and include the cellulose or woody fibre of cotton, linen, walls of plant cells, etc. They are usually indigestible, although, in tender cabbage and other very tender vegetables, they are digestible. Galactose found in sugar, seeds, and algae; pectans found in unripe fruit and the gummy exudate on trees and plants are also pentosans.
Starches and sugars are well known to everyone as they are found in all fruits and vegetables. Sugars are soluble carbohydrates with a more or less sweet taste. When heated to a high temperature they form caramel. Sugars are crystalloids, starches are insoluble and are colloids. Glycogen and milk sugar are the only carbohydrates of animal origin and even these are derived originally from the plant. Animals are incapable of extracting carbon from the air and synthesizing carbohydrates.
While the sugars are all soluble, raw starch is insoluble. Boiling will render part of it soluble. This, however, as will be shown in a later chapter, hinders its digestion. Starch is converted into a disaccharide in the mouth and this is, then, converted into a monosaccharide in the intestine.
The body cannot use starch. It must first be converted into sugar before it can be utilized by the cells. This is done in the process of digestion and begins in the mouth. Disaccharides and polysaccharides are converted into monosaccharides in the process of digestion, as carbohydrates can be absorbed and assimilated only as monosaccharides. Starch must first be converted into sugar and the complex sugars must be converted into simple sugars before they are absorbed. The body's need for sugar may easily be supplied without eating commercial sugars and syrups, or any form of denatured carbohydrate. Child and adult, alike, should eat only natural sweets and starches.
Sugar is the most important building material in the plant world. A characteristic difference between plants and animals is that, whereas, the animal is built up largely out of proteins, the plant is built up largely out of carbohydrates. Plants may be truly said to be made of sugar. They contain various minerals and some nitrogen, but practically the whole fabric of the plant or tree is composed of sugar in some form. Sugars are essential constituents of all plants without which they cannot exist. Indeed, sugars are the most important and most abundant building materials in plants. Out of the immature or sap sugars plants build their roots, stems, flowers, fruits and seeds. The finished plant is almost literally made of sugar.
Nature produces sugars out of three gases--carbon, oxygen and hydrogen. Oxygen and hydrogen in proportions to form water are taken from the water in the soil. Carbon is taken from the carbon dioxide of the air. Out of these gases, or out of this fluid and gas, the plant synthesizes sugar, a thing the animal cannot do. The green coloring of plants is due to the presence of a pigment known as chlorophyll. This pigment takes part in a chemical process known as photosynthesis, by which, carbon-dioxide (or, at least the carbon in the carbon-dioxide), with the aid of sunlight, is united with water to form sugar. Recent experiments have shown that enzymes contained in the leaves of the plants are the chief agents in the production of this sugar. Some plants can produce sugar in the absence of light.
Not only the starches of plants, but also the pentosans, the woody fibers, cellulose and gums are made of sugar and may be reconverted into sugar. When carbohydrates are stored for long periods they are stored as starches. When they are used, they are reconverted into sugars. Corn, peas, etc., are sweet (full of sugar) before they mature. The sap of the corn is also sweet. The sap of the cane plant is very sweet. In the matured state, corn, cane seed and peas are hard starch grains. In the germinating process the starch is reconverted into sugar. As starches, these seeds will keep for long periods of time; as sugars they would not keep until the following spring. It will be noticed that the enzymes in seed do not require ultra violet rays and acid to bring about this reconversion, any more than do the enzymes in digestive juices.
Fruits are ready for immediate use and if not used soon after ripening, tend to decompose rapidly. Grains are intended for storage. It is significant that fruits are composed of insoluble starches and are usually rich in acids before they ripen. In this state they are usually avoided by animals. The starch is reconverted into sugar in the ripening process. This arrangement protects the seed of the fruit until it is matured and ready for dispersal. Then the fruit is ripened and made ready for food.
The animal, like the plant, builds its carbohydrates out of sugar. All starch foods must be converted into sugar (in the process of digestion) before they can be taken into the body and used. Animal starch (glycogen) is made from sugar. It, like the starch of grains, is a storage product. Like the starch of grains, it must be reconverted into sugar before using. The sugar in milk may be made from starches.
The matured or fruit sugars of plants, especially those of fruits, are particularly appropriate for food. They are never concentrated and are always well balanced with other ingredients. They are built up out of the immature sugar and impart to both fresh and dried fruits their delicious flavors. Matured sugars in flowers are collected by bees and made into honey. Fruit sugars are, in truth, export products produced by plants.
All the sugar the body requires may be obtained from fresh ripe fruits. This is especially so during the summer months. During the winter months when fresh fruits are not so abundant, dried (but unsulphured) fruits are excellent sources of sugar. These should not be cooked. Owing to the absence of water, dried fruits are more concentrated foods then fresh fruits and should not be eaten in the same bulk.
Just as fruits are savoured with their matured sugars, so vegetable foods are savoured with the immature juices (saps) of the plants. In the plants, as in the fruits, the sugars are combined with vitamins, mineral salts, fibre and other elements of foods.
It is essential to emphasize that sugars constitute but one of the ingredients of plant life and are never put up in their pure state. In fruits and plants they are always combined with and balanced by other ingredients, particularly with salts, vitamins and water. Man, not nature, produces concentrated sugars. Man, not nature, separates the minerals from sugar. Sugars should be eaten as nature provides them.
Commercial syrups and molasses are concentrated saps. Besides being concentrated, usually by the use of heat in evaporating the water, they are commonly deprived of their minerals and vitamins, often have preservatives, artificial colors and flavors added and are often bleached with sulphur dioxide, with which they become saturated. Commercial sugars--maple, cane, beet, milk--are crystallized saps. They too, are unbalanced, commonly bleached, and thoroughly unfitted for use. So concentrated are these syrups and sugars, so denatured and so prone to speedy fermentation in the digestive tract, that it is best not to employ them at all. If they are used they should be used very sparingly. The same rule should apply to honey. This food of the bee contains all the other nutritive elements in very minute quantities, being largely water and sugar with flavors from the flowers. If it is eaten, it should be taken sparingly.
What a difference between eating sugar cane and eating the extracted, concentrated and refined sugar of the cane! It is said that it takes a West Indian native an hour to chew eighteen inches of cane from which he derives the equivalent of one large lump of sugar--less than the average coffee-drinker puts into a single cup of his favorite poison. (The boys and girls of Texas and Louisiana can chew sugar cane faster than the West Indian native, it seems.) In thus securing his sugar, the cane-eater secures the minerals and vitamins that are normally associated with sugars--he does not eat a "purified" product.
Sugar is regarded as an energy food, but it is a remarkable fact that the heavy sugar-eater prefers to watch athletic games to taking part in them. We, of course, have reference to the heavy-eater of commercial sugars. They seem to stimulate and then depress the muscular powers.
It has long been the Hygienic theory that the catarrhal diseases are based on carbohydrate excess--sugar excess, as all starches are converted into sugar in digestion. It is interesting to note, in this connection, that the British Medical Journal for June 1933 carried an article discussing "the relation of excessive carbohydrate ingestion to catarrh and other diseases," in which it was pointed out that during World War I, the incidence of catarrhal illnesses was reduced seemingly corresponding with the great reduction of sugar consumption. The writer of the article concludes that "restriction in the use of sugar would result in improvement in the national health as regards catarrhal illness, as well as in other directions."