

AVAILABILITY AND FUEL VALUE OF FOOD MATERIALS. IOI 

Using the figures for availability and heat of combustion of 
protein compounds given in Table 4 (page 86) and Table 6 
(page 92), and the factor 1.25 as expressing the amount of 
energy lost in the urine per gram of available protein, the cal- 
culation of the fuel value of protein is simple. We may take 
for instance the protein of meat. ‘This is assumed to have a 
heat of combustion of 5.65 calories per gram. Ninety-seven 
per cent. of this protein is rendered available for use in the 
body; the total energy of the available protein corresponding 
to 1 gram of total protein would be 5.5 calories (5.65  .97 
= 5.48). Of this 5.5 calories, however, 1.25 calories will be 
contained in the incompletely oxidized material of the urine, 
so that the actual amount of energy obtained by the body from 
the gram of protein eaten is equal to 4.25 calories (5.65 X .97 
— 1.25 4.23). In other words, on the basis of the previous 
assumption the fuel value of 1 gram of protein of meat is 4.25 
calories per gran. Ina similar manner we may calculate the 
fuel value of 1 gram of protein of cereals. The heat of com- 
bustion per gram is approximately 5.8 calories, and 85 per 
cent. of the protein appears to be available for use in the body. 
But for every gram of protein thus available not far from 1.25 
calories of energy is lost in the urine. The fuel value, there- 
fore, of r gram of protein of cereals as thus computed is 3.7 
calories (5.80 X .85 — 1.25 = 3.68). Similar computations 
give factors for fuel value of protein of eggs, dairy products, 
legumes, vegetables and fruits. The results of these calcula- 
tions are shown in Table ro beyond. 
In determining factors for fuel value of fats and carbohy- 
drates we have to consider only the total energy and the pro- 
‘portion actually available, since we assume that none of the 
energy of these nutrients is lost in the urine. It appears, for 
example, that 95 per cent. of the fat of meat is utilized within 
the body. ‘The average heat of combustion of 1 gram of meat 
fat is 9.5 calories, and the energy of the available material, 
which for fats is the same as its fuel value, would therefore be 9 
calories per gram (9.5 X .95—9.02). Inasimilar manner the 
fuel value of the carbohydrates is found by deducting the energy 
in the unavailable portion from the total energy. The heat of 
combustion of 1 gram of carbohydrates of cereals, for example, 
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