This section is from the book "Elements Of The Theory And Practice Of Cookery", by Mary E. Williams. Also available from Amazon: Elements Of The Theory And Practice Of Cookery; A Textbook Of Domestic Science For Use In Schools.
The body of a human being, like the bodies of most animals and plants, consists of parts called organs. The special work of each organ is called its function. What is the function of the eye? of the lungs? of the stomach? of a root? of a leaf? Organs differ from one another, not in function only, but also in make-up, or structure. The various kinds of material composing the organs of the body are called tissues. Bony tissue is found in bones and teeth, muscular tissue in muscles, and nervous tissue in nerves and brain. The tissues of the body are made up of cells, as the walls of a house are constructed of bricks. Instead, however, of being laid together, as bricks are, these cells grow together, each kind of tissue being built of similar cells of a particular kind.
One yeast-cell is much like another, but how about the cells in a grain of wheat? Starch-cells differ from bran-cells in structure because they differ in function. Each yeast-cell is independent, doing all its own work; but in higher forms of life, both plant and animal, where many cells are joined together in one individual, some have one function, some another. We may compare a yeast-plant to a man living alone, preparing his own food and making everything he needs, while a tree or a horse or the body of a human being is like a nation, in which some men are farmers, some manufacturers, some merchants, and so on. And just as the merchant does not understand farming, nor the man who raises wheat know how to make it into flour, so a cell of one kind cannot do the work of another. Cells in lung tissue, for example, are adapted for absorbing oxygen, and cells in the retina of the eye for receiving rays of light; but neither kind of cell is able to take in food until it has been prepared for them by the work of other cells. (Chap. 15.)
All living cells have for their basic sub-stance a very thin translucent jelly. This is protoplasm, the only thing in plants and animals that is really alive. The meaning of the word protoplasm is first-formed, or first-created.
Food contains five different classes of foodstuffs : protein, fat, carbohydrate, mineral matter, and water. Any food must contain at least one of the first four. We already know that protein builds tissue, and that fat, carbo-hydrate, and protein all are burned to supply energy, giving out heat in the process. (Pp. 71, 86.) The value of any food as an energy-producer is called its fuel value. The mineral part of food is often termed ash, because it is left, when all the rest of the food, even the carbon, is burned up. As this plainly shows, mineral matter has no fuel value, but it helps to build tissue. The organic acids in fruits and fermented foods have fuel value, though not so much as carbohydrates have. Water cannot be said to build tissue, but it keeps up the supply of water in both the tissues and the fluids of the body. Both water and mineral matter have a special work to do in keeping all tissues and fluids in healthy condition, and in taking an essential part in digestion and the various other processes which go on in the body.
Protoplasm cannot be made without protein, because only in protein is nitrogen found combined in a certain way with carbon, hydrogen, and oxygen. Plants draw up other nitrogen compounds from the soil and turn them into protein; but animals and man must obtain protein ready-made in their food. Therefore we require a certain amount of protein food, no matter how well supplied we may be with other foods. Proteins differ according to the way in which the elements in them are arranged. There is one kind of albumin in eggs, another in milk, another in meat. Some proteins contain, besides the five elements already mentioned, iron or phosphorus or both.
Proteins are not all equally good tissue-builders. The proteins of eggs and milk are among the best. Gelatin, found in cooked meat, and zein, the chief protein of maize, are among the poorest. Tissue cannot be built from either gelatin or zein alone. Indeed, proteins seem to build better when they work together. For this reason there is sense in our practice of using a variety of protein foods.
Although protein supplies both building-material- and fuel, so that in theory one might live upon protein (with water and mineral matter), it is more economical and in the long run more healthful to depend largely upon fat and carbohydrate for fuel. (Which kinds of food, generally speaking, are the most expensive, animal or vegetable? From which do we get most of our carbohydrate?) Any fat not used at once for fuel may be stored in the body until needed. A layer of fat under the skin protects against cold. As a rule carbohydrates are rapidly used up in producing energy, but they can be changed into fat and stored. Starch and sugar are the most abundant of carbohydrates. Dextrin occurs in smaller quantities. Glycogen is an animal carbohydrate something like dextrin. It is stored as reserve fuel; in men and animals mostly in the liver, but in shellfish more generally throughout the tissues.
The ash from a mixture of foods contains iron, sulphur, phosphorus, potassium, sodium, and other elements, mostly in the form of mineral salts. The only mineral salts not entering the body as a part of some food are common salt (sodium chloride) and the salts in mineral waters. Some of the salts in food are simply dissolved in animal fluids or plant juices. Others are joined to proteins. All of these elements are essential to healthy life, and as one element cannot take the place of another, it is important to eat a sufficient variety of food to supply them all. If we eat enough protein, we shall obtain all the sulphur we need, but we are not sure of getting enough iron or phosphorus. Lack of phosphorus is as harmful as lack of protein, phosphorus being necessary to many tissues, particularly to the brain and nerves. Phosphorus is supplied by milk, eggs, certain vegetables, and by cereal foods which include part at least of the outer layers of the grain, such as whole wheat and natural brown rice. Calcium gives hardness to bones and teeth. Calcium salts are plentiful in milk and cheese. Iron makes good red blood. There is much iron in lean meat, but it is found in a more nutritious form in milk, eggs, cereals, vegetables, and fruits. Salts also help to regulate digestion, circulation, and other body-processes.
Acid and alkali neutralize each other in the body as they do in baking-powder. (P. 109.) The alkalies found in the body have another name, bases. An excess of acid is not good for the health. An excess of bases does no harm. So we should eat enough base-forming foods to neutralize the acid present, or even a little more. At this point we have something unexpected to learn. The acids of fruits and vegetables do not remain acid in the body. They are changed into bases. The acids derived from food come from protein. (P. 370.) This may sound confusing ; but what we need to remember is simple. Meat, eggs, fish, and milk are acid-forming foods. Fruits and vegetables are base-forming foods. We should eat liberally of fruits and vegetables to neutralize the acid from protein foods. This gives us a second reason for eating potato with meat. What other reason is there ?
What we have learned makes it plain that the functions of food are: (l) to furnish energy, including heat, (2) to build tissue, (3) to regulate body-processes.
Food as purchased contains some uneatable material, inedible it is termed, such as egg-shells, pea-pods, bones. Other portions of the food, often considered waste, may be utilized. For example, fruit-parings may be made into jelly, meat-trimmings and celery-root used for soup.
Food-adjuncts are materials added to food for the sake of their flavor or their stimulating effect on taste, appetite, or digestion. They include condiments, such as spices, pepper, and vinegar; herbs; onion-juice and other vegetable flavorings; and the oils of the vanilla bean, of lemon, and of other fruits and some nuts. Salt and sugar are used as food-adjuncts as well as foods.
Beverages include drinks of all kinds. Tea, coffee, and cocoa are treated of in Chapter XII (Tea, Coffee, Cocoa). Beverages made with unfermented fruit-juices (fresh or preserved) are wholesome, and might well be more generally used in the home.
Alcoholic liquors (rum, whiskey, gin, brandy, wine, beer) 1 are made of the fermented juices of fruit or grain. (See pp. 130, 131.) They contain too little food material to be worth anything as food. Instead of satisfying hunger, alcohol produces an unnatural craving. In spite of the feeling of warmth it gives, it tends to lower the temperature of the body. It impairs the ability to work. It makes workmen careless and liable to accidents. It builds no tissue. On the contrary it injures tissue, particularly that of nerves and brain. It is unnecessary and so harmful that in a considerable part of the United States the sale of liquor is prohibited by law.
1 Brandy, rum, and whiskey usually contain from 40 to 50 per cent of alcohol, gin somewhat less. Wine contains from 7 to 16 per cent, beer usually 3.5 to 4 per cent of alcohol. Wine and beer drinkers, however, may drink such large quantities of these beverages that they get a great deal of alcohol. Root-beer made with yeast contains alcohol.
It has been found that people cannot keep healthy indefinitely on dried, canned, or otherwise artificially prepared foods, even though they contain all the foodstuffs. We need to have some of our food in its natural state, fresh, or even raw. It is supposed that fresh food, both animal and vegetable, contains minute quantities of substances, not nutritious in themselves, but essential to nutrition, and that these are affected by heat, and destroyed by prolonged cooking or drying. These sub-stances have been named vitamines and lipoids.
For further development of topics treated in this section see: -
Sherman : Chemistry of food and nutrition.
Sherman : Food products. In particular ch. 1.
Kinne and Cooley : Foods and household management. Ch. 18.
Hutchison: Food and the principles of dietetics. Especially ch. 9,
Alcohol. Greer : Food - what it is and does. Pp. 178-216. Chittenden : Nutrition of man. Stiles : Nutritional physiology. Ch. 24, Alcohol. Olsen : Pure foods. For condiments and spices see ch. 17 and 18. Mendel : Nutritive significance of different kinds of foodstuffs. Medical record, v. 85, no. 17, 1914. U. S. Dept. of Agriculture : Farmers' Bulletin. 142. Principles of nutrition. Snell : Elementary household science. Ch. 31-36. l
Ritchie : Primer of physiology. Ch. 1 and 2, The human body and the cells of which it is built. Bigelow : Applied biology. Chittenden : Nutrition of man.