In estimating the food requirement of a family it is usually preferable to consider each child's energy requirement directly rather than to count the children as equivalent to fractions of the hypothetical "average man."

Above the age of 17 years, although there is still some growth, differences in activity due to occupation become so great that the food requirement will usually depend as much upon occupation as upon age.

The fuel value of children's dietaries, should always be liberal in order to provide amply for muscular activity and for a more intense general metabolism than that of the adult. Furthermore, throughout the period of growth the food must supply a certain amount of material to be added to the body in the form of new tissue in addition to all that which is oxidized to support metabolism.

With the elderly, on the other hand, the intensity of metabolism is diminished and the body not only needs less food, but has less ability to deal with excess, so that the food requirement gradually declines and may become 10 or 20 per cent, or possibly even 30 per cent, lower than in middle life.

In the table on page 197 are given the estimated height, weight, and food requirement of an average man at different ages, the figures for height and weight being based upon the data given by Hill for males of the Anglo-Saxon and Teutonic races; (Recent Advances in Physiology and Biochemistry, page 284).

These estimates of food requirements are intended to represent approximate averages of available data and to allow for such exercise as would naturally be taken at the age, exclusive of anything which would ordinarily be considered physical labor. They thus illustrate in an approximate way the rate at which the amount of food required for healthy maintenance per unit of body weight declines from infancy to old age.

DuBois has recently published in graphic form his estimates of the basal energy metabolism per unit of body surface at different ages. The graph is reproduced by Lusk (Science of Nutrition, 3d edition, page 128).

The average basal metabolism, per unit of surface, found by DuBois in boys of 12 to 13, in men, and in women was as follows :

Average Basal Metabolism Of Boys, Men, And Women (Dubois)