To determine the energy value of a given amount of any food, it is necessary to know first its composition, i. e., the percentages of protein, fat, and carbohydrate present. Tables are available giving the results of many analyses, as in Bulletin 28, Office of Experiment Station, United States Dept. of Agriculture, Washington, D. C, "The Chemical Composition of American Food Materials".

Second

From these percentages to determine the weight of protein fat and carbohydrate in grams, which can be obtained from a given amount of the food material.

Third

To multiply these weights by the energy value of one gram of each of the three food principles.

By way of illustration let us find the fuel value of one loaf of bread, weighing 12 ounces.

(1) By referring to Bulletin 28, we find that white bread (miscellaneous) yields on the average, 9. 3 % protein. 1. 2 % fat. 52. 7 % carbohydrate.

(2) To get the weight of protein, fat and carbohydrate in grams, we must first convert the total weight of bread into grams, 1 oz. =3 28. 35 grams. 12 oz. = 340. 2 grams. Then 340. 2 X 0. 093 = 31. 64 grams of protein. 340. 2 X 0. 012 = 4. 08 grams of fat. 340. 2 X 0. 527 = 179. 28 grams of carbohydrate.

(3) Multiplying the amount of each nutrient by the proper factor,

Hence the total energy value of 1 loaf of bread weighing 12 ounces is 880.4 calories.

To calculate the total energy value of any combination of foods, it is necessary to compute the fuel value of each ingredient, and take the sum of the whole group.

Thus for Egg Broth, page 118, it is necessary first to get the weight in grams of each of the following ingredients and then to estimate their energy value as indicated above.

Yolk of 1 egg.........................= 13 grams.

1 tablespoon sugar....................= 15 grams.

1 cup milk............................= 244 grams.

1 tablespoon brandy...................= 14 grams.

In this book the food values of all the materials used have been incorporated into a table, so that by reference to this the value of any combination is quickly made.

1 The energy value of alcohol is 7 calories per gram. It is necessary, therefore, to know the per cent. of alcohol in any liquor.

To estimate the fuel value of any diet, it is simply necessary to compute the food value of each food material used and add the results together.

To estimate the fuel value of an infant's diet, the following formula, adapted to the above factors for energy value from Friedenwald and Ruhrah's Diet in Health and Disease, is very convenient.

Formula for calculating the Calories of Any Period of 'Infant Feeding:

(1) Quantity X F X 2. 65 = Calories from fat.

(2) Quantity X (S + P) X 1. 18 = Calories from protein and sugar.

The sum of 1 and 2 gives the total calories.

Quantity = 24-hour amount in ounces. F, S and P = fat, sugar, and protein respectively, with percents in whole numbers.

To illustrate, take a formula of the following composition:

Protein ..................................... 0. 7%

Fat ......................................... 2. 7%

Carbohydrates ............................... 6. 0%.

{Feedings per day 9, amount at each finding 1½ oz.

Hence Q=13.5 oz. (9X 1½) F = 2.7 oz. S= 6 oz. P= 0.7 oz.

(1) Q. X F X 2.65 = 13.5 X 2.7 X 2.65 = 96.6 Cal.

(2) Q. X (S + P) X 1.18 = 13.5 X (6 + 0.7) X 1.18 = 106.7 Cal.

96.6 + 106.7 = 203.3 Cal., total for day.