The question will probably come to each one - of how much practical use for the everyday housekeeper is this study of dietaries. In the first place, it would mean the expenditure of a great deal of time if one should undertake to determine each day's rations in this way. In the next place, it is impossible to know the actual composition of the food that we eat, except in a few cases. We may be fairly sure of the composition of the egg, but when meat varies in proteid from 12 per cent to 22 per cent as it does according to the Atwater analyses, how are we to determine the composition of the particular cut that we are using to-day? Moreover, even if our meal were prepared so that the exact proportions of nutrients were furnished, it is quite possible that one member of the family might eat too large a proportion of the pro-teids and another too much of the carbohydrates.
Another element of uncertainty lies in the difference in composition between cooked and uncooked food. Rice, for example, according to the tables, contains 79 per cent of carbohydrate and 7.8 per cent of proteid. But if you. will weigh a cup of rice before it is cooked, and the same rice after it is cooked, you will find that it has gained perhaps four times its original weight. In other words, a quarter of a pound of cooked rice will only furnish about a fourth as much nutrient as a quarter of a pound of rice without the added water. Often we can allow for this difference in the calculation of our dietary; but sometimes we know too little about the changes which take place in cooking to do this. Finally, even if we know exactly what we eat we do not know what we assimilate. Is there, then, any use in the dietary standard? In two ways it is of great service. In the first place, it is a standard by which we may test our diet if we extend our experiment over a sufficiently long period. At the beginning of a month let us take account of stock, estimate the amount of food materials on hand, and then keep careful account for a month of all food brought into the house; at the end of the month we will again estimate what we have on hand and in this way ascertain the amount of raw material used. Table IV, with the details which follow, gives an example of a carefully calculated dietary. The composition of the various foods,was taken from Bulletin No. 28 of the office of Experiment Stations, U. S. Department of Agriculture.* If, on calculating the food value of the different materials, we find that for the number of persons served we have a distinct variation from the standard diet, we can legitimately conclude that there is something- wrong. If, for example, we find that the amount of proteid calculated in our food materials is twice as much as that supposed to be required, we shall conclude that either our families must be using a much larger amount of proteid than would be conducive to the best health, or there must be much unnecessary waste, and in either case, an investigation would be needed.
* "The Chemical Composition of American Food Materials" which may be obtained by sending five cents in coin to the U. S. Department of Agriculture, Office of Experiment Stations, Washington, D. C.