The ultimate aim of scientific knowledge relating to human nutrition should be to promote the healthful and economical use of food. Unless this knowledge has a practical application, it serves merely as an object of intellectual interest. A person may determine what he shall eat from two points of view, viz., he may select his food on the basis of rational considerations of health and economy, or he may sensuously follow the dictates of appetite. It is to be feared that the latter point of view largely prevails. Man does not seem to regulate his diet wisely by an intuitive sense of what is best for his physical welfare, but in a large number of cases is the unfortunate victim of unbridled indulgence in that which most delights his taste, but eventually ruins his health. If reason dominates, then many questions come to the front, some of which are the following:

1. The amounts and proportions of the various foods that best meet the physiological requirements of different classes of persons in their varying conditions of age, activity, and environment.

2. The selection of food materials that will supply a diet physiologically adequate and efficient for a given purpose.

3. The economical purchase of a food supply.

4. Methods of preparing foods to secure dietetic efficiency and the minimum waste.

5. The preservation of food.

6. Food sanitation.

Our physiological food requirements and the influence of various conditions of age, activity, and environment upon these requirements, as shown by eating habits.

It is hoped that in the preceding pages it has been made clear that through the matter and energy supplied in food the human body is constructed and its activities maintained. It should also be plain that as the different food compounds have unlike functions, all of these must be found in a diet that will build and sustain a normal human body. We cannot avoid the conclusion either, that as food supplies the raw material for the growth of body tissue as well as the fuel used to maintain the work performed by the human machine both internally and externally, food consumption must necessarily vary greatly with different individuals.