General Physiologic Considerations. Composition of Human Body and of Foods. Alteration of Foods in Process of Digestion, Absorption, and Utilization. Classification.

Dietotherapy is the application of foods to the preservation of strength, flesh, and energy, or to their repair when diminished by disease. Necessarily the value of foods in health must be understood in order to appreciate their relative utility in disease.

The human body contains the following chemical elements: Carbon, hydrogen, oxygen, nitrogen, sulphur, phosphorus, chlorin, iodin, potassium, sodium, calcium, magnesium, and iron. A few other elements have been found in the human body, but they are not uniformly present. The first four named occur in much larger proportions than the others. It is self-evident that food that is to make an infant's body grow to man's dimensions and capacity must contain these elements. It is, however, impossible to feed human beings upon chemical elements. To be useful they must be furnished in certain combinations.

The following table shows the composition of foods. In the processes of digestion and assimilation many of these compounds are transformed into others which are peculiar to the human body. Therefore the chemical composition of the human body is not an adequate guide to the foods which are useful.