THE WORLD'S DIET What Constitutes a Good Diet.—The conditions of agriculture and civilization discussed in previous chapters determine the kind of food that people eat. The food has much to do with health and strength. A good diet must contain three main elements—carbo hydrates, fats, and proteids. Carbohydrates are substances such as starch and sugar, which, like fats are composed of carbon, hydrogen, and oxygen. The carbon is slowly burned in our bodies, and thus gives us warmth and energy. Proteids are substances such as cheese, meat, and -fish, containing nitrogen. They are necessary because without them the body cannot build new tissues and repair its con tinual waste. An ordinary adult man engaged on ordinary work requires about eighteen ounces of carbohydrates or fats and 4 to 41 ounces of proteids per day. For children, sick people, or those who are working very hard, the amount is different, but in general the carbohydrates and fats should be four or five times as abundant as the proteids.
In addition to the three main food substances there is need of smaller quantities of salts, vitamines, and the acids of fruits. A good diet should contain not only the right amount of these and of carbo hydrates, fats, and proteids, but should vary from day to day so that people may not get tired of it, and may be sure to get all the needed elements. Aside from the prosperous inhabitants of advanced countries, however, the majority of the world's people live largely on a few kinds of food.
A Table of Food Values.—The value of the food used in different parts of the world may be judged from the table given below. Col umn A shows the kind of food; B, C, and D show what percentage of each kind is waste material like (B) skin and bones, (C) water, or (D) mineral matter, such as salt. Column E gives the percentage of actual food materials in the various articles as we buy them in the market. It will be seen that this varies from only 9 per cent in beets which contain much water and a good deal of waste, to 90 per cent in oatmeal and 100 per cent in sugar.
Columns F and G should be considered together. Column F
shows how many pounds of a given article would have to be pur chased in order to get from it 41 ounces of proteids, the daily require ment of an active adult man. Column G shows how many pounds would be needed in order to get the daily requirement of 18 ounces of carbohydrates or fats. In many cases a sufficient supply of both types of food could not be got from a single article without eating an enormous quantity. For instance, suppose a person has to live for a while on nothing but fresh cod, as often happens to the Labrador fisherman. About 2.5 pounds of fresh fish would supply the needed proteids. An ordinary person could easily eat this quantity in a day. Codfish are so lean, however, that 564 pounds would have to be eaten to get enough carbohydrates and fats.
Or suppose a Korean peasant has no supplies except dried beans, would he be as well off as a Turkoman nomad east of the Caspian Sea who has no food except cheese? About 1.2 pounds of dried beans and 1.1 of cheese would be needed for proteids, while 1.8 pounds of beans would have to be eaten to get enough carbonaceous material, and over 3 of cheese. Therefore the Korean with legumes like beans and peas is better off than the nomad with cheese. In order to get enough carbohydrates or fats from cheese the stomach would have to be over loaded with three times as much proteid as it needs and would thus be injured.
In Column H the whole matter is summed up by means of index numbers. A value of 1 means that an article contains the right proportion of proteids and carbonaceous materials. Anything between 1 and 2 forms a fairly good article of diet even by itself. A plus sign means that carbohydrates or fats predominate and a minus sign indicates an excess of proteids. In a good diet the plus articles, carbonaceous, should balance the minus ones with much proteids. Thus beef just about balances sweet potatoes, and chicken balances bana:nas. On the other hand, a little butter with its great predom inance of fat balances a large amount of beans with their slight excess of proteid.