This section is from the book "Practical Dietetics With Special Reference To Diet In Disease", by William Gilman Thompson. Also available from Amazon: Practical Dietetics with Special Reference to Diet in Disease.
The principal salts derived from the food are as follows:
Chlorides of sodium and potassium; carbonates of sodium, potassium and magnesium; sulphates of sodium, potassium and magnesium; phosphates of sodium, potassium, magnesium, and calcium. The majority of these salts are held to be unaltered by digestive processes and pass into the blood or tissues without necessary chemical change. The reason for this belief is the fact of the readiness with which they can be obtained, unaltered by chemical analysis, from the different tissues of the body and the urine. Some compounds - namely, the salts of iron and salts of the organic acids - are ingested in very minute quantity and their uses are but vaguely understood. Other salts, such as the chlorides, carbonates, and phosphates of the alkalies and alkaline earths, are taken in much larger daily amount and subserve definite purposes.
The uses of the salts derived from the food are summarised as follows:
I. To regulate the specific gravity of the blood and other fluids of the body.
II. To regulate the chemical reaction of the blood and the various secretions and excretions.
III. To preserve the tissues from disorganisation and putrefaction.
IV. To control the rate of absorption by osmosis.
V. To enter into the permanent composition of certain structures, especially the bones and teeth.
VI. To enable the blood to hold certain materials in solution.
VII. To serve special purposes, such, for example, as the influence of sodium chloride on hydrochloric-acid formation, and that of lime salts in favouring coagulation of the blood.
Salts of any kind when taken in excess with the food disagree with digestion in various ways. They may prove locally irritant to the gastric or intestinal mucous membrane; they modify the rate of absorption of digestive material, and alter the intensity of reaction of the different digestive fluids. After being absorbed in excess they may interfere with the nutritive and chemical processes of the blood and tissues. Some persons acquire a salt-eating habit and partake too freely of common salt with the food, with the result of the production of more or less dyspepsia or some of the symptoms above mentioned. Too much salt in the food produces thirst, and may even stimulate a craving for strong drink.
Continued deprivation of any one of the common salts, so long as others are furnished in reasonable abundance in the food, does not result seriously. If, however, all the salts are reduced in quantity, of if they are entirely excluded from the diet, the system very soon begins to evince signs of malnutrition. This is readily accounted for by referring to the uses of salts above described. Animals or men deprived of salts for a long time suffer greatly from indigestion and from lack of bodily nutrition. The body may not diminish in weight, but the tissues become "flabby," the muscles feeble, the mind stupid and dull, the nutrition of the skin is altered, it becomes dry, and there is falling out of the hair. Eventually, in animals with salt starvation death occurs in from six to eight weeks from progressive bodily weakness and inanition - a condition, practically, of marasmus.
Young infants who do not obtain sufficient salts of lime - i. e., if fed upon proprietary "infant foods " instead of good milk - become rhachitic; their bones ossify slowly and bend into deformities. Such children are sometimes given hypophosphite-of-lime biscuits to supply the deficiency, but they should be properly fed upon fresh milk. (See Rhachitis).