This is done by multiplying the entire number of grams of food given by the amount of protein, fat and carbohydrate contained in one gram, then multiplying these results by the physiological fuel factor of each. Thus 100 grams of milk would yield
| 100 × .033 | = | 3.3 × 4 | = | 13.2 calories from protein |
| 100 × .040 | = | 4.0 × 9 | = | 36.0 calories from fat |
| 100 × .050 | = | 5.0 × 4 | = | 20.0 calories from carbohydrates |
| or a total of | 69.2 calories from 100 grams of milk. | |||
The Standard or 100 Calorie Portion.—Just as it has been more convenient to estimate a larger rather than a smaller quantity of food material, so it is frequently more desirable to estimate a hundred calories, rather than one calorie. This is especially useful when dietaries of high caloric (fuel) value are to be estimated, or dietaries in which foods of like composition and fuel value are to be interchangeable. In such cases it is a simple matter to select the desired number of 100 calorie portions of those foods which are to make up the dietary.[19]
Method of Estimating the 100 Calorie Portion.—The number of calories yielded by 100 grams of food material is taken as a basis upon which to estimate the 100 calorie portion, and X represents the number of grams required to yield this portion. The problem is one of “simple proportion,” for example, take the 100 grams of milk just estimated, we found that 100 grams (or c.c.) furnished 69.2 calories of heat, then, 100:69.2 :: X:100—145; or 145 grams of milk are required to furnish 100 calories of heat. Suppose it is desirable to substitute eggs for a part of the milk in the diet, eggs have a higher fuel value per unit of weight than milk, their average composition being 13.4% protein, and 10.5% fat (no appreciable amount of carbohydrates), 100 grams of eggs would yield
| 100 × .134 | = | 13.4 × 4 | = | 53.6 calories from protein |
| 100 × .105 | = | 10.5 × 9 | = | 94.5 calories from fat, |
| or a total of | 148 calories. | |||
The Standard or 100 calorie portion of eggs would be,
100:148 :: X:100 = 68
or the number of grams required to yield 100 calories.
Thus it is seen that in using the fuel value of a hundred grams of food material for estimating the standard or 100 calories portion the extremes are always the same. Hence, the weight of the 100 calorie portion may always be obtained by multiplying the extremes and dividing the result by the number of calories furnished by 100 grams of food material.