Foods and the Theory of Digestion : Part 2

Physiology and Hygiene for Secondary Schools
by Francis M. Walters

(Page 10 of 27)

Fats. - The fats used as foods belong to one or the other of two classes, known as solid fats and oils. The solid fats are derived chiefly from animals, and the oils are obtained mostly from plants. Butter, the fat of meats, olive oil, and the oil of nuts are the fats of greatest importance as foods. Fats, like the carbohydrates, are composed of carbon, hydrogen, and oxygen. They are rather complex chemical compounds, though not so complex as proteins. Since neither fats nor carbohydrates contain nitrogen, they are frequently classed together as non-nitrogenous foods.

Purpose Served by Carbohydrates, Fats, and Albuminoids. - These classes of nutrients all serve the common purpose of supplying energy. By uniting with oxygen at the cells, they supply heat and the other forms of bodily force. This is perhaps their only purpose. proteins also serve this purpose, but they are not so well adapted to supplying energy as are the carbohydrates and the fats. In the first place they do not completely oxidize and therefore do not supply so much energy; and, in the second place, they form waste products that are removed with difficulty from the body.

Mineral Salts and their Uses. - Mineral salts are found in small quantities in all of the more common food materials, and, as a rule, find their way into the body unnoticed. They supply the elements which are found in the body in small quantities and serve a variety of purposes. Calcium phosphate and calcium carbonate are important constituents of the bones and teeth; and the salts containing iron renew the hemoglobin of the blood. Others perform important functions in the vital processes. The mineral compound of greatest importance perhaps is sodium chloride, or common salt. This is a natural constituent of most of our foods, and is also added to food in its preparation for the table. When it is withheld from animals for a considerable length of time, they suffer intensely and finally die. It is necessary in the blood and lymph to keep their constituents in solution, and is thought to play an important role in the chemical changes of the cells. It is constantly leaving the body as a waste product and must be constantly supplied in small quantities in the foods.

Importance of Water. - Water finds its way into the body as a pure liquid, as a part of such mixtures as coffee, chocolate, and milk, and as a constituent of all our solid foods. It is also formed in the body by the oxidation of hydrogen. It passes through the body unchanged, and is constantly being removed by all the organs of excretion. Though water does not liberate energy in the body nor build up the tissues in the sense that other foods do, it is as necessary to the maintenance of life as oxygen or proteins. It occurs in all the tissues, and forms about 70 percent of the entire weight of the body. Its presence is necessary for the interchange of materials at the cells and for keeping the tissues soft and pliable. As it enters the body, it carries digested food substances with it, and as it leaves it is loaded with wastes. Its chief physiological work, which is that of a transporter of material, depends upon its ability to dissolve substances and to flow readily from place to place.

Relative Quantity of Nutrients Needed. - proteins, carbohydrates, and fats are the nutrients that supply most of the body's nourishment. The most hygienic diet is the one which supplies the proteins in sufficient quantity to rebuild the tissues and the carbohydrates and fats in the right amounts to supply the body with energy. Much experimenting has been done with a view to determining these proportions, but the results so far are not entirely satisfactory. According to some of the older estimates, a person of average size requires for his daily use five ounces of protein, two and one half ounces of fat, and fifteen ounces of carbohydrate. Recent investigations of this problem seem to show that the body is as well, if not better, nourished by a much smaller amount of protein - not more than two and one half ounces.

While there is probably no necessity for the healthy individual's taking his protein, fat, and carbohydrate in exact proportions (if the proportions best suited to his body were known), the fact needs to be emphasized that proteins, although absolutely necessary, should form but a small part (not over one fifth) of the daily bill of fare. In recognition of this fact is involved a principle of health and also one of economy. The proteins, especially those in meats, are the most expensive of the nutrients, whereas the carbohydrates, which should form the greater bulk of one's food, are the least expensive.

Effects of a One-sided Diet. - The plan of the body is such as to require a mixed diet, and all of the great classes of nutrients are necessary. If one could subsist on any single class, it would be proteins, for proteins are able both to rebuild tissue and to supply energy. But if proteins are eaten much in excess of the body's need for rebuilding the tissues, and this excess is oxidized for supplying energy, a strain is thrown upon the organs of excretion, because of the increase in the wastes. Not only is there danger of overworking certain of these organs (the liver and kidneys), but the wastes may linger too long in the body, causing disorder and laying the foundation for disease. On the other hand, if an insufficient amount of protein is taken, the tissues are improperly nourished, and one is unable to exert his usual strength. What is true of the proteins is true, though in a different way, of the other great classes of foods. A diet which is lacking in protein, carbohydrate, or fat, or which has any one of them in excess, is not adapted to the requirements of the body.

Composition of the Food Materials. - One who intelligently provides the daily bill of fare must have some knowledge of the nature and quantity of the nutrients present in the different materials used as food. This information is supplied by the chemist, who has made extensive analyses for this purpose.

Food Supply to the Table. - The main problem in supplying the daily bill of fare is that of securing through the different food materials the requisite amounts of proteins, carbohydrates, and fats. In this matter a table showing the composition of foods can be used to great advantage. Consulting the table on page 126, it is seen that large percents of proteins are supplied by lean meat, eggs, cheese, beans, peas, peanuts, and oatmeal, while fat is in excess in fat meat, butter, and nuts. Carbohydrates are supplied in abundance by potatoes, rice, corn, sugar, and molasses. The different cereals also contain a large percentage of carbohydrates in the form of starch.

Variety in the selection of foods for the table is an essential feature, but this should not increase either the work or the expense of supplying the meals. Each single meal can, and should, be simple in itself and, at the same time, differ sufficiently from the meal preceding and the one following to give the necessary variety in the course of the day. The bill of fare should, of course, include fruits (for their tonic effects) and very small amounts perhaps of substances which stimulate the appetite, such as pepper, mustard, etc., known as condiments.

D.C. Heath and Co. - Publishers
Original copyright 1909