the fuel value of protein
foods, due allowance must be made for these losses. Allowance must
also be made for the incomplete digestion, or losses occurring in the
digestion, of the foodstuffs. These losses, as well as the approximate
amount of each constituent absorbed, are represented in the following
table.[17]

===========================+===========+===============
| _Lost_ | _Absorbed_
---------------------------+-----------+---------------
Carbohydrates |2 per cent.| 98 per cent.
Fats |5 per cent.| 95 per cent.
Proteins |8 per cent.| 92 per cent.
===========================+===========+===============

The physiological fuel factors of food, or the amount of heat produced
as the result of combustion of 1 gram of organic food material after
the above-mentioned losses have been accounted for, may be obtained as
follows.[18]

=================================================
Carbohydrates 4.1 x 98% = 4 cal. per gram
Fats 9.45 x 95% = 9 cal. per gram
Proteins 4.35 x 92% = 4 cal. per gram
=================================================

EFFECT OF HEAT AND COLD UPON THE FOODSTUFFS

In primeval days, when man led a more natural life, his very existence
depended upon his ability to wrest from the earth his 4--9--4; these,
then, constitute what are known as the "physiological fuel factors" of
carbohydrates, fats, and proteins respectively.

~Determination of Fuel Value of Food.~--In determining the amount of
heat produced by a given amount of food, it is first essential to
reduce the amount to grams (for example, 1 lb. equals 480 grams):
first, because the gram is a unit of weight commonly used in dietetic
calculations; second, because the fuel factors are based on the amount
of heat produced by the burning of one gram of organic foodstuffs.
Knowing the composition of food, that is the number of hundredths of
protein, carbohydrate and fat it contains, it is a simple matter to
estimate its fuel value by multiplying the amount of each contained in
one gram by its physiological fuel factor 4.4.9. Thus if the
composition of a food is 3-3/10% protein, 4% fat and 5% carbohydrate,
one gram would contain .033 gram of protein, .04 gram of fat and 0.5
gram of carbohydrate. Hence one gram of milk would produce

.033 x 4 = .132 calorie from protein
.04 x 9 = .36 calorie from fat