THE NORMAL DIET OF MAN 697 



In children a computation of the energy requirements is rendered more 

 difficult by two factors. In the first place the processes of growth are 

 attended with an active metabolism, so that the metabolism is more energetic 

 in the young animal than in the adult, even if we take into account the 

 relative surfaces in the two cases. Thus the basal metabolism per square 

 metre in boys of varying ages was found by Du Bois to be as follows : 



Mean \ee Basal Metabolism P er 



square metre per hour 



6-5 . . . . . 57-5 



12-6 ..... 50-4 



13-7 494 



16-5 43 



19-25 40-7 



In addition to this increased basal metabolism, if the processes of growth 

 are to occur normally, there must be an excess of matter taken with the 

 food over that excreted, since the growing animal is always putting on 

 weight. Between the ages of eleven and sixteen both sexes put on weight 

 at about 4 kilos a year", which is equivalent to adding to the body a store 

 of about 800 Calories per month. The. second difficulty is due to the fact 

 that, while children do not perform any measurable work, they are in a 

 constant state of muscular activity, and this aimless activity of a child is of 

 great value in determining its healthy nervous and muscular development. 

 The amount of this activity seems related to the amount of food taken 

 the increased energy of a child directly after a meal is a familiar pheno- 

 menon. If food is withheld or diminished this activity declines, but in this 

 way energy is saved and the whole of the lessened food may go to maintain 

 the temperature of the body and the normal processes of growth. 



We may thus obtain a development of the child not differing appre- 

 ciably from the normal on widely varying amounts of food, and it becomes 

 difficult to say what is the average or the optimum amount that a child 

 should have. Judging from the analysis of the food actually taken in the 

 families of working men and others in receipt of sufficient incomes, it would 

 appear that the amounts laid down by Lusk do not err on the insufficient 

 side, although they are far iess than are actually given in many well-to-do 

 families and in high class schools, where great importance is attached to 

 games and other forms of exercise. Lusk expresses the requirements of the 

 different classes and ages in terms of the ' average man ' taken as 1 . 



Class Coefficient Energy Requirements 



Average man ....... 1 3000 



Average woman 0-83 2500 



Children 0-6 (both sexes) . . . .0-5 1500 



6-10 . . . . 0-7 2100 



10-14 .... 0-83 2500 



Girls 14 upwards 0-83 2500 



Boys 14 upwards ...... 1 3000 



These figur.es represent the actual energy output of the average individual, 

 and are therefore equivalent to the food which must be digested and absorbed 



