Function of Water.—The uses of water in the body are many, and the advantage arising from a sufficient amount of this foodstuff in the dietary cannot be overestimated. It is no longer considered an error in diet to drink a moderate amount of water with the meals, so long as it is not used as a substitute for mastication, and as a means of washing the food into the stomach. In the diet, both as a beverage and as a part of most of the food materials ingested, water serves to moisten the tissues; to furnish the fluid medium for all of the secretions and excretions of the body; to carry food materials in solution to all parts of the organism; to stimulate secretory cells producing the digestive juices, thereby aiding in the processes of digestion, absorption and excretion; to promote circulation; to furnish material for free diuresis, thus preventing to a great extent the retention of injurious substances by the body, which might otherwise take place.
Factors Determining the Amount of Water Needed.—In normal conditions it is probable that the kind and amount of exercise taken has more to do with the amount of water needed by the body than any other factor, since the vigorously worked body excretes more water by way of the skin than the quiescent one. With a normal amount of exercise, it is advisable to drink from six to eight glasses of water each day, increasing the amount to a certain extent when exercise causes a great loss through perspiration. It is always advisable, however, to keep in mind that an excessive amount of fluid taken into the body throws a corresponding amount of work on the organs (the stomach, kidneys and heart). In certain abnormal conditions, the body’s water supply is depleted. This is particularly true in the case of hemorrhage, vomiting, and diarrhea. Under other conditions (certain types of nephritis), the body becomes overburdened through the excess of water retained, owing to the difficulty which the kidneys show in eliminating it. This retention of water by the tissues gives rise to the condition known as edema.
MINERAL SALTS
Ash.—The eight remaining chemical elements, i.e., calcium, magnesium, sulphur, iron, sodium, potassium, phosphorus, chlorine, constituting the mineral salts or ash, are likewise classed as food on account of the work which they perform in the body. Some of these elements enter the body as essential constituents of the organic compounds, and are metabolized in the body as such, becoming inorganic only upon oxidation of the organic materials of which they form a part.
Importance of the Mineral Salts.—The way in which the mineral elements exist in the body and take part in its functions, has been graphically outlined by Sherman as follows.
“(1) As bone constituents, giving rigidity and relative permanence to the skeletal tissues. (2) As essential elements of the organic compounds which are the chief solids of the soft tissues (muscles, blood cells, etc.). (3) As soluble salts (electrolytes) held in solution in the fluids of the body; giving to those fluids their characteristic influence upon the elasticity and irritability of muscle and nerve; supplying material for the acidity and alkalinity of the digestive juices and other secretions; and yet maintaining the neutrality, or slight alkalescence, of the internal fluids as well as their osmotic pressure and solvent power.”[9]
The above outline, showing the various ways in which the mineral constituents enter and take part in the various functions, as well as in the structure of the body, make it evident that the same close attention and study which was given to the other foodstuffs must be accorded to these substances. When the student realizes that the presence of certain salts dissolved in the blood assists in the regulation of the vital processes of the body such as the digestion, circulation and respiration; that they are responsible for the contraction and relaxation of the muscles; that they assist in controlling the nerves; that they are, in a way, instrumental in releasing the energy locked up in food—the value of these elements becomes very evident, and their importance in the dietary inestimable. Some of the mineral salts are more widely distributed in food than others, and the danger arising from their deficiency in the diet is not so great as is the case with others; hence attention is called to those found by investigators to be most often lacking or deficient in the average diet; i.e., calcium, phosphorus, and iron. A brief summary of the special parts played by these elements will be outlined here.
Calcium.—Physiology teaches that about eighty-five per cent. of the mineral matter of the bone, or at least three-quarters of the ash of the entire body, consists of calcium phosphates. It has long been known that this mineral salt is necessary for the coagulation of the blood, and science has demonstrated that “the alternate contractions and relaxations which constitute the normal beating of the heart are dependent, at least in part, upon the presence of a sufficient, but not excessive concentration of calcium salts in the fluid which bathes the heart muscles.”[10]
Phosphorus.—According to Sherman, phosphorus compounds are as widely distributed in the body, and as strictly essential to every living cell as are proteins. Science has also proved that they are important constituents in the skeleton, in milk, in glandular tissue, in sexual elements, and in the nervous system; that these compounds take part in the functions of cell multiplication, in the activation and control of enzyme actions, in the maintenance of neutrality in the body; that they exert an influence on the osmotic pressure and surface tension of the body, and upon the processes of absorption and secretion. Like calcium, phosphorus is absolutely essential to the growth and development of the body, and, as in the case of the mineral, its presence in the dietary must be accorded strict attention, in order to avoid the results accruing from its deficiency. Casein, or caseinogen of milk and egg yolk (ovovitellin), are the substances richest in this mineral salt. The fact that the phosphorus existing in grains (cereals) may be removed largely in the process of milling, makes it advisable to consider the use of the breads made from the whole grains.
Iron.—The presence of iron as an essential constituent of hemoglobin has already been discussed. That which is not in the hemoglobin is chiefly found in the chromatin substances of the cells.