The quantity of food required to maintain the body in a vigorous condition depends upon the following conditions:—­(1) Climate and season, (2) clothing, (3) occupation, (4) age and sex.  In civilized countries more food is eaten, as a rule, than is necessary to maintain health and strength.  Climate and seasons influence the quantity of food eaten.  A cold, bracing atmosphere stimulates the appetite, tempts one to exercise, while a hot climate has the contrary effect; hence the need for more or less food.  Abundant clothing in cold weather conserves the body heat; less food is therefore required to maintain life.  Exercise and muscular work cause greater oxidation in the tissues and greater waste of the muscles; this must be replaced by proper food.  Outdoor work requires more food than indoor, and physical labor more than mental.  It has been estimated “that a child of ten years requires half as much food as a grown woman, and one of fourteen an equal amount.  The rapidly growing active boy often eats as much as a man, and the middle-aged man requires more than the aged.  A man of seventy years may preserve health on a quantity which would soon starve his grandson.”

Just what ingredients of the food serve for nourishment of the brain and nerves, and how they do that service, are mysteries which have not yet been solved.  Brain and nerve contain the elements nitrogen and phosphorus, which are found in protein compounds but not in the true fats, sugars, and starches, which contain only carbon, hydrogen and oxygen.  We naturally infer that the protein compounds must be especially concerned in building up brain and nerve, and keeping them in repair.  Just how much food the brain worker needs is a question which has not yet been decided.  In general it appears that a man or a woman whose occupation is what we call sedentary, who is without vigorous exercise and does but little hard muscular work, needs much less than the man at hard manual labor, and that the brain worker needs comparatively little of carbohydrates or fats.  Many physicians, physiologists and students of hygiene have become convinced that well-to-do people, whose work is mental rather than physical, eat too much; that the diet of people of this class as a whole is one-sided as well as excessive, and that the principal evil is the use of too much fat, starch and sugar.  It is well to remember that it is the quantity of food digested which builds the body, and more injury is likely to result from over-eating than from a restricted diet, hence the value of having food cooked so as to aid digestion.  The following dietary standards may be interesting to the more advanced pupils, housewives, etc.:—­

STANDARDS FOR DAILY DIET OF LABORING MAN AT MODERATE MUSCULAR WORK.