Proteins, Carbohydrates And Fats
( Originally Published 1938 )
The nutritive parts of the food we eat are called the five food elements. They are the proteins, carbohydrates, fats, mineral matter and water. Recently a sixth element has been added the vitamins. However, as they are not used directly for energy or for tissue-building.
Protein is the element of which our tissues are made. Therefore it is absolutely necessary to eat a certain amount of foods containing protein.
The white of an egg is the purest form of protein in our ordinary foods. Naturally, since protein is the basis of all animal tissue, it is also found in meat and fish, and in dairy products such as milk and cheese. Certain vegetables contain a large amount of protein. Among such are green beans, lima beans, lentils and peas. Cereals and nuts also contain a goodly amount of protein, but fruits have only a negligible amount. Protein is absolutely essential for good health. Indeed, an adult could fare quite well on a diet exclusively protein if necessary. But he could not live on a diet composed only of fats and carbohydrates. This is because fats and starches cannot take the place of protein in the building of tissues, while protein can be used for energy.
Protein is an essential part of every cell in the body, although to be sure, it is present in relatively small amounts in bone and fat which are sometimes called the inactive tissues. On the other hand, by far the greater part of active or muscle tissue, both voluntary and involuntary are composed of protein. About twenty-five percent of the muscles is composed of solid matter. Of this about four-fifths is protein material. Thus it should be self-evident that we must eat a certain amount of protein.
Protein may also be used as fuel for muscular work if it is necessary, but at a great expense to the body, and only when other material is not available, since it is essential for the building and repair of tissues. The old idea that in some way muscular tissue is broken down when work is done is entirely erroneous.
That it is erroneous is very evident when you consider the muscles of your favorite athlete. They do not reduce, but grow in size when he is in training and doing hard muscular work regularly. The fats and carbohydrates in his balanced diet supply most of the energy; and his muscles, instead of being consumed or broken down, are in such a fine condition as a result of regular exercise that they acquire a new firmness and a somewhat larger size.
Yet, in spite of it all, the misconception still persists that foods rich in protein are "strengthening" and that an athlete or any one else doing heavy muscular work needs an extra amount of meat, especially juicy red beef, because he is doing so much muscular work and consuming so much energy. Without exercise, regardless of the amount of protein eaten, muscles remain soft and flabby.
Yet the fact is, as we have said, that although protein may be used as fuel when absolutely necessary, it is a disadvantageous and uneconomical form of fuel. This is immediately clear when you understand the fate of protein in your body. One part of the digested protein is taken from the bloodstream and built up into tissue protein material, that is it is used for the building and repair of tissues. For this use the amino acids into which the proteins are broken down in the process of digestion are kept whole and their distinguishing element, called nitrogen, is not separated from them but is incorporated in the new tissue. The protein so used represents the actual protein requirement of the body.
Now this only represents a part of the protein consumed, which is generally considerably in excess of the protein needed for building and repair of tissues. The body must be rid of the excess protein for it cannot store protein. It must be burned up and the products of this burning or oxidation as it is called, must be excreted. But first it must be converted into a form that can be burned. The nitrogen is split off or separated from the excess protein and is changed into certain nitrogen containing substances which are thrown off by the kidneys. The fragments which contain no nitrogen are then oxidized just as the carbohydrates and fats are. Thus the nitrogen, which was indispensable to tissue building, becomes the very opposite when it is necessary to use protein as fuel. This is one of the reasons why protein is an expensive form of fuel. Another reason is that when protein is burned it leaves an acid ash. In another chapter we shall learn that the reaction of the body tissues should be almost neutral, with a slight inclination towards the alkaline side. Serious disturbances are likely to result if the alkaline reserve is lowered because it has been used to neutralize the excess acid.
But even if protein is an expensive form of fuel, the fact remains that a certain amount is absolutely necessary for the life of the tissues and consequently for life itself.
Carbohydrate is the general term for all starches and sugars. Indeed, the starches are nothing but many sugar groups linked together which when digested, separate into simple sugars again because the links or bonds which hold them together are broken.
Most people think there is only one sugar, the ordinary sugar, made from cane or beets, and scientifically called sucrose. There are, however, four other sugars commonly consumed.
Glucose, also known as dextrose or grape sugar, is found abundantly in fruits and plant juices. It is especially abundant in grapes, and among the vegetables is found in large quantities in sweet corn, onions and unripe potatoes.
Fructose or fruit sugar is found in plant juices, fruits and especially in honey of which nearly one-half of the solid matter is fructose.
Lactose is the name given to the sugar found in the milk of all animals. It is less sweet than sucrose and has been found less irritating to the lining of the stomach. Many people have found it an important aid in maintaining a healthy intestinal condition.
Maltose or malt sugar is an important constituent of germinating cereals, malt and malt products.
Sucrose is not only derived from the sugar beet and sugar cane, but also from sorghum and the sugar maple. Many of the common vegetables and fruits, too, contain noticeable amounts. It is said to constitute, for example, at least half the solid portion of pineapples and of some roots such as carrots.
Starch is the form in which most plants store by far the greatest part of their carbohydrate material. It is found stored in seeds, roots, tubers, bulbs and sometimes the leaves and stalks of plants. Fully one-half to three fourths of the solid portion of the ordinary cereal grains such as wheat, oats and rye, is composed of starch. At least three-fourths of the solids of mature potatoes is starch, but don't let that stop you from eating them even if you are overweight. Potatoes are at least seventy-five percent water so the three fourths starch content has little significance. Besides potatoes are highly valuable for their mineral and vitamin content.
Unripe fruits such as apples and bananas contain much starch, but as they ripen most of the starch is changed into the simpler sugars. On the other hand, young, tender corn or maize and peas contain sugar which is changed into starch as these seeds, which they really are, although we are not apt to think of them as such, ripen.
Glycogen serves much the same purpose in animals that starch plays in plants and it is therefore frequently called animal starch. It occurs in the lower as well as the higher animals, in all parts of the body, but especially in the liver which serves as a storehouse for glycogen.
The carbohydrates constitute the largest portion of our food because they are the most economical source of energy. They contain a large percentage of carbon (hence carbohydrates) which unites readily with oxygen, forming carbon dioxide among other elements in burning.
In the process of digestion the more complex forms of starches and sugars are broken down into the simplest form glucose.
It is this glucose which is the fuel of the body. However, it is not used in the body exactly in this form. After it has been absorbed into the blood stream from the intestines, nearly all the glucose is carried to the liver. Here it is converted into glycogen or animal starch of which we spoke of before. Then, when any of the body tissues, the muscles, for example, need energy, the liver sends out the glycogen which it has stored.
In the muscles the glycogen is changed back into glucose, and then burned. Some glycogen, you will recall, can be stored in the muscles themselves.
In addition to serving as fuel, carbohydrates may form fatty tissue. Evidence of this is given by overweight persons who all too freely partake of candy, cereals, bread and cake and other foods rich in carbohydrates.
Fats are liberally distributed in nature and are found in both the animal and vegetable foods. They are in milk, cream, butter, whole-milk cheeses, egg yolk, nuts, and vegetable oils such as olive, peanut, cottonseed and corn oils. The fatty portions of meat and fish, of course, are largely composed of fat.
After the fat has been digested, the end-products are absorbed into the lymph vessels and then are eventually emptied into the blood stream. After a fat-rich meal tiny particles of fat may be seen in the blood.
The blood stream carries the fat to the tissues of the body. There, if necessary, it may be burned at once as energy. The same amount of fat gives forth more than twice as much energy as an equal amount of carbohydrate. However, it is not as economical for this purpose as the carbohydrate foods, and is only burned when the supply of the latter is not sufficient.
If the fat is not needed at once for energy, some of it may be converted into glycogen and stored for future use, but far the greater portion is transformed into fatty tissue and deposited about the internal organs or under the skin. These fat deposits not only act as a reserve fuel supply, but they protect the organs and hold them in place. In this way the organs can perform their functions to the best advantage and without strain. This is particularly true of the abdominal organs the kidneys, the intestines and the other organs are largely held in place by fatty tissue. If you need any proof of the importance of this function, just contrast the jolly disposition and good digestion of the fat man with the miserableness of the thin, nervous, highly irritable man who frequently is suffering from indigestion and sagging abdominal organs.
Fat also acts as a buffer against external jarring and injury of the organs, particularly the nerve centers. Here again is a reason for the proverbial good nature of the fat man. His large nerve centers are protected from mechanical irritation with fat.
Fat offers still another service to the nerves. Some of it enters into combination with the proteins, phosphorus and other substances to form complex compounds which are used to build nerve tissue.
The temperature of the body, as you know, is pretty constant unless one is ill. Fat tissue helps to maintain this constant temperature. It is a poor conductor of heat, and so acts as an insulator, preventing the loss of heat from the body in cold weather and preventing the rise of body temperature when the temperature of the surrounding atmosphere is above normal body temperature. You doubtlessly remember the days when your mother piled heavy, fatty foods into you when you had to brave a blizzard to get to school. She probably didn't think of fat as an insulator, but she knew that fat was heating and "stuck to your ribs".
This brings us to the last and yet one of the most important services that fat renders us, a service that every good cook knows, whether she prefer the butter of the French, the olive oil of the Italians or the lard of the Germans. Fat both imparts flavor to and brings out or intensifies the flavor of our food. It gives pastry its delectable, tender flakiness; it imparts that delicate, fine texture to cake that makes it impossible to resist a second helping; and to everything fried or baked, it gives a crispy, golden brown crust that is a delight to the eye as well as the palate. Indeed, it is no exaggeration to say that fat is the basis of all palatable cooking. And palatability is allessential to good digestion, as we shall soon see.
Thus we see that a certain amount of fat is absolutely necessary for good health. An excess of fat in the body, to be sure, carries serious disadvantages, but a normal amount of fatty tissue is a great safety factor. The person who is a little above what is considered his normal weight usually has a more stable nervous system and is less susceptible to infectious diseases than one who is underweight. Therefore the absurd reducing craze, which, fortunately, seems to be on the wane, is to be lamented. It has been responsible for a great deal of ill-health and unhappiness. The movies have been largely responsible for the craze, for our favorite stars appear to be so "willowy". This is largely a trick of photography and skillful dressing. If you don't believe it, the next time you go to the movies, carefully observe the anatomy of the actors. I'm willing to wager that even among the most sylph like heroines, you won't see a row of buttons down her spine, or a Venetian-blind effect across her chest. A layer of fat is as necessary for beauty as for health; it is fat that gives the beautiful rounded contours and the soft, smooth, youthful skin.