CHAPTER I
PURPOSES OF FOOD

The purposes of food are:

To supply the material out of which the body may rebuild the tissues.

To produce heat, and to liberate muscular and mental energy.

Every particle of body substance is constantly changing. The new material for cells and tissues, the substance to supply the energy needed in the metabolic work of tearing down and rebuilding, the energy used in the digestive process of converting the food into condition to be assimilated, and the energy used in muscular, brain, and nerve movement must all be supplied by food.

Every effort of the brain in the process of thinking, every motion, and every muscular movement requires energy which the food must supply.

The body is composed of a vast number of cells varying according to the tissue or organ in which they are found. The characteristic of all living matter is that it constantly reproduces itself. Cells perform their appointed work, wear out, and must be replaced by new ones or derangements follow.

The new cells constantly being formed, increase in size and in so doing push the worn-out, dying, and dead cells out of the way. The process of building and eliminating continues within the body and on its surface every instant of life.

An idea of the number of dead cells constantly being thrown off from every part of the body may be gained by noticing the amount of dead skin cast off. The fine scales of “scarf” or “dead” skin, which we easily rub off in a friction bath, are composed of these dead cells which have been crowded out by the hosts of vital cells constantly forming beneath. The process is the same in every tissue and organ. The dead or worn-out matter within the body is burned by oxygen and put in condition to be carried by the blood to the organs of elimination, the kidneys, intestines, lungs, and skin.

Much waste is eliminated in liquid form through the sweat glands. It is said that stokers throw off four pounds of water and waste a day through the skin.

In the growing child the process of building and of eliminating is active and rapid. In the youth it is less rapid, in the adult still less, but unless the process is kept active, stagnation and death ensue.

Daily exercise is necessary to keep up the body activities; yet very few take the trouble to secure daily a complete, thorough circulation of blood, especially through the vital organs and the deeper tissues. Perfect circulation is the key-note of health.

Activity of any kind necessitates the expenditure of energy. The process is a chemical one and in all chemical processes heat is necessary to cause the decomposition of elements and their recomposition into different substances.

Heat in its turn has two functions. It enables the chemical changes to be carried on which fit the food for the use of the various tissues, and it burns to an ash the worn-out products of the body’s activity, fitting them for elimination.

It keeps the tissues flexible and the secretions fluid; coagulation takes place when the secretions become cold.

As previously stated, food in the body, then, is needed for two purposes:

(1) to build and maintain the cell until its work is done;

(2) to furnish the heat necessary to decompose the food into its elements, and to produce the energy by which all the body processes are carried on.

That the food may be appropriated by the body it must be not only proper in kind and quantity, but the body must also be in condition to digest, absorb, and assimilate it and to eliminate the waste, otherwise the body needs are not met.

It is the nourishment which the body assimilates and appropriates to its needs which counts in food economy, not necessarily the amount consumed.

Therefore if the food is to economically serve its purpose, the body must be in a condition to digest and assimilate it—this condition depends largely on perfect circulation, correct position of organs, and correct breathing habits.

Of the fifteen to twenty substances contained in foods and comprised in the body, the principal ones are oxygen, hydrogen, carbon, nitrogen, chlorin, sodium, potassium, magnesium, iron, calcium, phosphorus, and sulphur. The differences in the forms of matter lie in the proportions in which these elements are combined.

Those containing the largest proportion of nitrogen are called Nitrogenous foods or Protein—such as meat, eggs, and some vegetables.

Those containing the largest proportion of carbon are known as Carbonaceous—such as cereals, sugar, and fat.

The four food elements, indispensable to life, either of plant or animal, are oxygen, hydrogen, carbon and nitrogen.

Carbon combined with oxygen forms carbon dioxid.

Oxygen, nitrogen, and carbon dioxid largely form the air.

Oxygen and hydrogen form water.

Calcium, iron, magnesium, sodium, and potassium are used in the formation of the various tissues and secretions of the body.

The substances contained in living organisms are the same as those in inorganic matter, only in different complexities as appropriated to the needs of each organism.

The difference between living and non-living matter is in the relative proportion and arrangement of the same elements.

Before it is fit to supply the needs of the body, the raw material must undergo a chemical change.

It has been demonstrated by scientific investigation that no unorganized elements, such as pure nitrogen, pure iron or magnesium, are assimilated by the system and converted into its various structures.

While the body needs carbon, it cannot use coal; it needs nitrogen, yet it cannot appropriate it to rebuilding bone and muscle, until, by chemical action with other elements, it has been converted into complex substances called proteins.

The muscles, ligaments, and labor-performing structures contain the largest amount of nitrogen.

The fat contains the largest amount of carbon.

The brain, the nerves, and the bones contain the largest proportion of phosphorus compounds.

Yet, while the brain contains phosphorus, and the tissues nitrogen, the brain cannot be built up by eating elementary phosphorus, nor the muscles by pure nitrogen, but compounds rich in phosphorus or nitrogen may be utilized.

Plants use the simple compounds of the earth, air, and soil, and, within their own cells, build them up into such complex substances as starch, sugar, protein, fat, and salts, putting them in condition for man and other animals to appropriate to their use.

All plant life is compounded from the elements in the soil, air, and water, by the action of the sun’s rays. The rays of heat and light store something of their power in latent heat and energy in these plant compounds.

The end of plant life is the completion of its compounds—when it has matured them, the plant dies.

All organic matter is thus formed by the action of the sun’s rays on inorganic matter.

The gluten of wheat is formed from the chemical union of nitrogen in the air and nitrogen in the soil with other substances.

The starch of wheat and other grains is from carbon which the plant has taken from the soil and combined with other substances.

All meats are largely derived from plants which have appropriated the elements from the soil, water, and air. The chemical processes of the animal convert the energy latent in the plant foods into the more concentrated form of meat. The animal thus performs a part of the chemical work for man—the digestive organs of one animal convert the food contained in certain plants, into a substance more easily assimilated by another animal.

Man would need to eat a large amount of nitrogen-containing plants in order to get as much protein as is contained in one egg or in a piece of lean meat the size of an egg. It is because the nitrogen is in such condensed form in meat and eggs that one is likely to take more than the system can handle, if he eats too freely of these two foods, particularly of meat. We will discuss this question more fully under “Proteins.”

Most domestic animals take their food elements from air and water, as well as from the compounds which the plants have formed, while wild animals and some domestic ones, such as hogs and chickens, make use of meat as well.

The greater part of muscle, nerve, and gland is composed of protein.

When the muscles are exercised constantly they use up their protein and must have it resupplied, or the muscle substance will waste. When the muscles are exercised freely, as in the laborer, or the athlete, they need more building material.

The skeleton is composed largely of deposited salts, as calcium. If, therefore, the growing child be not supplied with a sufficient amount of this substance, the bones will be weak and liable to deformity and the teeth will be slow in coming or will be small and malformed. Children need foods rich in lime.

The elements which supply heat and keep up muscular activity are starches, fats, and sugars.

It must be apparent to every thoughtful person, that, since the nerves, muscles, and glands are composed largely of protein and the skeleton largely of calcium salts, in order to furnish the body with the elements necessary for growth and repair, all of these elements, as also the energy-producing substances, must be provided.

Each individual, therefore, should learn how much he requires to replace his daily waste, both for rebuilding tissue and for supplying heat and energy.

The day laborer, though he may do more muscular work than an athlete in training, expends scarcely any nervous energy. Therefore he needs less protein in his diet than one does who expends both nervous and muscular activity, as does the athlete.