It is my purpose in this chapter to lay down a few general principles to aid you in the practical problem of selecting the best diet for yourself. But it must be made clear at the outset that there can be no hard and fast rule. All human bodies are more or less alike, but on the other hand all are more or less different. Modern civilization has given very few bodies the chance to be perfect; nearly all have some weakness, some abnormality, and need some special modification in diet to fit their particular problem. The ideal in each case would be a complete study of the individual system. Some day, no doubt, medical science will analyze the digestive juices and the gland secretions and the blood-stream of every human being, and say, you need a certain percentage of starch and a certain percentage of protein; you need such and such proportion of phosphorus and iron; you should avoid certain acids--and so on. But at present we are devoting our science to the task of killing and maiming other people, instead of enabling ourselves to live in health and happiness; so it is that most of those who read this book will be too poor to command the advice of a diet specialist. The best you can do is to get a few general ideas and try them out, watching your own body and learning its peculiarities. Human food contains three elements: proteins, fats and carbohydrates. The proteins are the body-building material, and the foods which are rich in proteins are lean meat, the white of eggs, milk and cheese, nuts, peas and beans. A certain amount of this kind of food is needed by the body. If it is missing, the body will gradually waste away. If too much of it is taken, the body can turn it into energy-making material, but this is a wasteful process, and the best evidence appears to be that it is a strain upon the system. Experiments conducted by Professor Chittenden of Yale have proven conclusively that men can live and maintain body weight upon much less protein food than previous dietetic standards had indicated. The fats are found in fat meats and dairy products, and in nuts, olives, and vegetable oils. The body is prepared to digest and assimilate a certain amount of fat, no one knows how much. I have found in my own case that I require a great deal less than people ordinarily eat. I have for many years maintained good health upon a diet containing no more fat than one gets with lean meat once or twice a day. I never use butter or olive oil, nor any fat in cooking. My reason for this is that fats are the most highly concentrated form of food, and the easiest upon which to overeat. Excess of fat is a cause, not merely of obesity, but also of boils and pimples and "pasty" complexion, and other signs of a clogged blood-stream.