The large amount of food required by infants relatively to their weight has been referred to above in the section dealing with the relation between diet and the extent of surface and rate of growth and some of the experimental data discussed. The proportions of the three food elements which are required may be taken to be those which are provided by nature in the mother's milk.
As the infant grows into the child, although the rate of growth becomes less, there is a much greater expenditure of energy in the muscles owing to the constant activity of a child, and the supply of food per kilogramme requires to be kept at about the same level. A boy of four weighing 2 stone 4 lb., just recovered from a slight surgical operation, who was kept in the hospital for a time, and whose food was weighed, was found to be taking 121 calories per kilogramme, which was made up as follows :
Bread, 8 oz.; butter, 1 oz.; eggs, 6 oz. (3 small eggs); milk, a pint; cream, 1 oz.; milk pudding, 8 oz.; jam, 1 oz.
This contains :
Protein, 63; fat, 72; carbo-hydrate, 202; calories, 1,757; and gives 43 grammes of protein per kilogramme.
A boy suffering from amyotonia congenita of nearly the same age and weight took a similar diet containing 110 calories and 4 grammes of protein per kilogramme. In this case muscular activity was almost at a minimum, but the boy was very thin, and a plentiful diet would be required to make up for the loss of heat] from his relatively greater surface.
The amount of protein per kilogramme is much greater than is taken by adults, but it is difficult to compare the figures, and it is clearer to express the percentage of the total heat value of the diet which is derived from protein; this is 15 per cent in each of these boys, which is a little above the proportion of protein in our standard diet for adults. About 40 per cent of the total heat value was furnished by fat. It would be obviously unwise at a period of rapid growth to limit the protein and, as a general rule, it may be said that the proportion both of protein and fat in the food of children should be kept up.
Children of school age again take a high proportion of calories. The writer is indebted to the Governor of the Duke of York's Royal Military School and to Major Dyke for particulars of the food taken by 540 boys in that school for a week. The average age was 12 1/2 years; the boys were weighed during the period, and their average weight was 5 stone 4.85 lb. The time of year was June. In this week the food supplied was equivalent to 94 calories per kilogramme; 13 per cent of the total energy was derived from protein, and about 8 per cent from fat. The ration is therefore a liberal one, but would be improved by a larger proportion of fat.
Mr. C. H. S. Frankau, F.R.C.S., has kindly furnished particulars of the dietary of an orphan school near London. The food taken by 401 children of the average age of 11 years and 10 months, of whom 260 were boys and 141 girls, amounted to 2,300 calories for each child per day. If the average weight be assumed to be about 5 stone, this is equivalent to 73 calories per kilogramme. The quantity of food is therefore less than is provided in the Duke of York's School. Probably the children in the latter school take more exercise, especially as they are all boys. The proportion of the total energy derived from protein, 15 per cent, is about the same, whilst that from fat, 23 per cent, is higher than in the Duke of York's school.
In general terms it has been calculated that a child about 8 years old requires half the food of an adult, and that a child of 16 years old will eat nearly, or quite as much, as an adult of ordinary weight and of sedentary occupation.