What foods to select, how they should be combined and proportioned, is determined mainly by laws dependent upon the following conditions:

  1. Age.
  2. Temperature of environment—time of year or climate.
  3. Work or activity.

(1) As to age:

If we wish the best results we must select and proportion our food according to age, because the growing child or youth needs much structural material—calcium phosphates—with which to build bone, teeth, and cartilage. This is found in cereals and in all grain foods. The middle-aged person needs but little of these—just enough for repair, and the aged person needs practically none.

While the growing child needs calcium phosphate, he also needs milk and natural sweets, which named in the order of their preference are honey, maple-sugar, dates, figs, and raisins. This does not mean that a generous quantity of vegetables and fruit cannot be taken, but that the articles first mentioned (cereals and starchy foods) should form a conspicuous part of the child's diet.

The adult needs a much less quantity of the heavier starchy foods, because the structural part of the body has been built up. The diet of the adult should consist of vegetables, nuts, and a normal quantity of sweets, a normal quantity of fruits, milk and eggs, with rather a limited amount of cereal or bread products, while the aged, or those having passed sixty, could subsist wholly upon a non-starch diet (non-cereal starch), such as vegetables, milk, nuts, eggs, salads, and fruits, including bananas, which is not a fruit, but a vegetable, and which contains a splendid form of readily soluble starch.

(2) As to time of year:

In selecting and proportioning our food we should observe the laws of temperature or time of the year. We should not eat foods of a high caloric or heating value at a time when the sun is giving us this heat direct, thus building a fire inside, while the sun is giving us the same heat outside. The violation of this simple law is the cause of all sunstroke and heat prostrations. On the contrary, if we are going to be exposed to zero weather, we should build a fire inside by eating foods of a high caloric value.

(3) As to work or activity: