ELEMENTS OF NUTRITION
There are seven distinct elements entering into the composition of human foods—protein, starch, sugar, fat, salts, cellulose, and water, not to mention enzymes, vitamines, and other little-known chemical principles. These elements are all variously concerned in the nourishment, energizing, and warming of the body.
PROTEINS
The proteins are the structure builders of the body. While starches, fats, and sugars may be compared to the coal that feeds the locomotive, the proteins represent the iron and steel that are used from time to time to repair the engine and replace its worn parts. The essential chemical difference between starch and protein is that the latter contains nitrogen and a small amount of sulphur and phosphorus. The most common forms in which protein is used for food are the glutens of the grains, the legumes, nuts, cheese, the white of egg, and lean meat.
STARCHES
The starches are by far the most abundant of all elements in human food. They enter largely into the composition of nearly all plants and seeds. Under the influence of the sunlight, the green-colored plants gather up the CO2 of the air and, with the water absorbed from the ground, build up starch. The plant takes all the carbon from which starch is made from the air, but while the atmosphere contains almost eighty per cent of nitrogen, the plant is unable to use it; it must secure its nitrogen from the decaying refuse of the soil. Thus the plant utilizes the waste products found in air and earth in the building of its food substances.
Starch exists in the form of small granules. Since each little starch granule is surrounded by a woody envelope of cellulose, it becomes necessary to cook all starches thoroughly in order to burst this cellulose envelope and thus enable the saliva to begin, and other secretions to continue, the work of digestion.
FRUIT SUGARS
The sugar of fruits represents a form of food requiring practically no digestion; while the sugar found in beets, the cane plant, and the maple tree, must be acted upon by the digestive juices of the intestine before their absorption can take place. During the winter, the maple tree stores its carbohydrates in its roots in the form of starch. With the advent of spring Mother Nature begins the digestion of this starch—actually turns it into sugar—and in the form of the sweet sap it finds its way up into the tree trunk to be deposited in the leaves and bark in the form of cellulose, a process very similar to that performed by digestion in the human body, where starch by digestion is first turned into sugar, and afterwards deposited in another form in the liver and muscles.
Dextrine is a form of sugar resulting from thoroughly cooking or partially digesting starch. There are about twenty-five stages or forms of dextrine between raw starch and digested starch or fruit sugar. Dextrine is found in the brown-colored portions of well-toasted bread.