The importance of a duly proportioned and sufficient dietary is shown by its great influence on health and constitution. An ill-proportioned or deficient diet is certain to lead to failure of health. The anatomy of an animal may be modified in the course of generations by altered diet, as well as its character; thus, the alimentary canal of the cat has increased in length to adapt it to its omnivorous habits. In the case of the bee we have a still more remarkable instance. If by any accident the queen bee dies, or is lost, the working bees (which are sexually undeveloped) select two or three eggs, which they hatch in large cells, and then feed the maggot on a stimulating jelly, different from that supplied to the other maggots, thus producing a queen bee.
The food of mankind varies naturally with—
I.—Climate. A cold climate leads to increased metabolism, and consequently a large amount of fatty matter can be eaten without producing nausea. Witness the difference between a Laplander’s and a Hindoo’s diet.
The season of the year has likewise some influence. Vital processes are more active in spring than autumn, and more food is consequently required in the former season.
II.—Occupation. Although muscular exercise is not associated with an immediate increase of elimination of urea, yet as a matter of experience more nitrogenous food is required and can be metabolised by hard workers than by idlers. The trappers on the North American prairies can live for weeks together on meat alone, accompanied by copious draughts of tea. They are constantly in the open air, undergoing fatiguing exercises, in a dry and rare atmosphere. For brain workers no special food is required. Foods containing phosphorus have no special value, so far as is known, for mental work. Such work, however, is apt to affect digestion; consequently the digestibility of food is more important for those engaged in sedentary occupations than its chemical composition.
III.—Sex. As a rule, women require about one-tenth less food than men, but probably this rule hardly holds good in the case of women engaged in laborious work.
IV.—Age. Infants require only milk, and the less they have of any other food before a year old the better. Atwater has calculated that——
- A child under 2 requires 3 ∕ 10 the food of a man doing moderate work.
- A child of 3 to 5 requires 4 ∕ 10 the food of a man doing moderate work.
- A child of 6 to 9 requires 5 ∕ 10 the food of a man doing moderate work.
- A child of 10 to 13 requires 6 ∕ 10 the food of a man doing moderate work.
- A girl of 14 to 16 requires 7 ∕ 10 the food of a man doing moderate work.
- A boy of 14 to 16 requires 8 ∕ 10 the food of a man doing moderate work.
Vital processes are more active in early life, and food is required not only to carry on the functions of the body, but also to furnish the materials for growth. Hence, while the proportion of proteids to carbohydrates and fats should be—
As 1:5.3 in adults, it should be about as 1:4.3 in children.