Another way in which the dietary standard is of especial service, is in enabling us to judge what error in diet is responsible for some particular weakness or peculiarity in any member of the family. A girl of fourteen may be unusually thin or may appear languid and tired, and everything point to improper feeding as the cause. The first thing to do in this case would be to see whether the child's diet were deficient in any one of the three nutrients, and if so bring the diet up to the standard. In dealing with abnormal conditions, then, or with large masses of people, or with diet over an extended length of time, the dietary standards may be applied to great advantage. It is not necessary to apply it strictly to each individual at each meal.
The calculation of a few dietaries is very useful in giving us a definite idea of the general composition of foods, and so making it easier to estimate the amount of different nutrients which we are providing at ordinary meals, without the tediousness of reckoning each meal in detail.
In such calculations the following factors are used to reduce the results to the standard of one man at moderate work.
Factors used by the U. S. Department of Agriculture in Calculating Meals Consumed in Dietary Studies.
Man at hard muscular work requires 1.2 the food of a man at moderately active muscular work.
Man with light muscular work and and boy 15-16 years old require 0.9 the food of a man at moderately active muscular work.
Man at sedentary occupation, woman at moderately active work, boy 13-14, and girl 15-16 years old require 0.8 the food of a man at moderately active muscular work.
Woman at light work, boy 12, and girl 13-14 years old require 0.7 the food of a man at moderately active muscular work.
Boy 10-11 and girl 10-12 years old require 0.6 the food of a man at moderately active muscular work.
Child 6-9 years old requires 0.5 the food of a man at moderately active muscular work.
Child 2-5 years old requires 0.4 the food of a man at moderately active muscular work.
Child under 2 years old requires 0.3 the food of a man at moderately active muscular work.
In making dietary studies all food used should be weighed, but the following data may be of use for approximate home calculation:
1 measuring cup=1/2 pint. 16 tablespoons =1 cup. 3 teaspoons=1 tablespoon. A cup of water weighs about 8.3 oz., of milk 8.6 oz., of cream 8.4 oz., of butter 8.4 oz., of lard 7.5 oz., of sugar 8 oz., and a tablespoonful of the foregoing weighs about 0.5 oz. A cup of meal weighs 5 oz., of sifted flour 4 oz., of oatmeal 2.7 oz., of cream of wheat 6 oz. A cubic inch of meat or butter weighs about 0.5 oz. An egg without shell weighs 1.6 oz. A slice of bread 1/2 in. thick weighs 1 oz., a heaping teaspoonful of sugar 0.4 oz.
Since the foregoing was written, Professor Irving Fisher of Yale University has devised a comparatively simple method of calculating individual dietaries. His method is given in full in Bulletin No. 13, "Food Values," of the A. S. H. E, and in the supplement to this series of lessons. Before going further it is well to become familiar with this method.
Instead of starting with the percentage composition by weight of foods, the basis is percentage by "food units" or fuel and energy value, or in other words, by calories. This does away with the varying amounts of water contained in food which, while absolutely necessary, has no fuel value and the method places the fats on the same basis as the carbohydrates and proteins.
A table is given showing the average food units required for men, women and children, based on Professor Chittenden's standards.
After becoming familiar with this method, the approximate total food value of one's daily diet may be reckoned mentally and the proportion of the three chief food principles may be obtained with but little figuring.
Note the additional work required by this method in connection with Question 21 of this lesson p. 217.