FOOD REQUIREMENTS: PRODUCTION AND RETAIL I. The activities of the cellular tissues of the body require that the necessary material for growth, for renewal of the worn tissues and for energy be supplied. This material constitutes food. From it the body liberates the necessary energy and secures new material for replacement purposes. Cellular activity is in different directions and for each type of activity different raw materials must be furnished. The most impor tant raw materials which the body requires are protein food and certain mineral salts. The importance of protein arises from its nitrogenous content and hence it serves chiefly in repair and new growth, and to a lesser extent as a source of energy. The energy requirements are chiefly met by carbonaceous foods. The mineral salts are required to maintain tonicity of the body fluids, to build up the solid tissues, to form hemoglobin and for other purposes.
The determination of the value of any given substance as a food is not a simple matter. Several different aspects must be considered. First perhaps, must be considered the percentage chemical composition of the substance. It must be assayed to determine its value in terms of food constituents, such as pro tein, carbohydrates, fats and inert material. A second test to determine suitability is of a physical character, and enables us to judge the value of the food stuff as a fuel or source of energy. It is usually calculated from the results of the chemical analysis by the employment of the following factors, and is expressed in calories: gm. of protein will produce 4.1 calories gm. of carbohydrate will produce .... 4.1 calories gm. of fat will produce 9.3 calories However, since different food stuffs are not consumed in the body to the same degree, those factors will not always give an accurate idea of the value of a food as fuel. Next one must consider the food stuff from the body's standpoint. It must be one which is capable of digestion and absorption by the body, and of meeting the body's needs. Different individuals are capable of utilizing different materials to different degrees. In general 92.6 per cent. of protein; 94.4 per cent. of carbohy drate and 97 per cent. of fat are absorbed. Some few, such as sugar are practically entirely absorbed. A fourth and equally as important guide to judgment is the knowledge whether a given food stuff can be obtained at a reasonable cost.
In general the following represents what may be considered a standard in the United States for the proportion in which the different food elements should be represented in the diet of adults each day.
Protein 12 5 gms. X 4.1 = 512 . 5 calories Carbohydrates.... 400 gms. X 4.1 = 1640. calories Fat 125 gms. X 9.3 = 1161.5 calories Some variation in these proportions can be made without in jury but a certain amount of protein is absolutely necessary, though the exact limit is not known. A further important factor in considering the protein element is whether its content of amino acids is of the one or more types which the body can rebuild into its own protein. If the amino acids are unsuitable, the protein present is useless.
Of the food consumed, less than one-sixth furnishes energy for work, the balance being lost as heat. In this respect the body's requirements and use of food are similar to the fuel consumption of an engine. Similarly more work requires more food. An average adult male of i5o pounds weight engaged different activities has approximately the following daily fuel requirements: Resting in bed 2000 calories Resting in a chair 2 230 calories Light work 2600 calories Moderate muscular work 310o calories Severe muscular work 3500 calories The energy for the extra work is chiefly supplied by the car bonaceous foods.
2. Food is essential to life and because of this requirement, food production everywhere is a fundamental industry and is the principal basis of agricultural pursuits. From the standpoint of raw materials or source, food stuffs are either animal or vegetable in origin. From a hygienic standpoint, the animal foods are of greater importance than the vegetable, as has been shown in Chapter XIX. With the animal foods we can group meat, fowl, fish, shellfish, crustaceans, insects and their products, eggs, milk and dairy products, animal fats and gelatine. The vegetable foods comprise cereals, vegetables proper, fruits, sugar, gums, vegetable oils and fats. While the production of these food stuffs is the basis of agriculture and fishing pursuits, yet many as produced are not suitable for im mediate use as food, or if suitable they require treatment to remove bulky, inert, and useless material, or to preserve them suitably for transportation. Around these processes have grown up a host of secondary industries. It is apparent therefore that industries based upon food stuffs are at the foundation of our economic life, as the need for food is at the foundation of our physical life.