

AVAILABILITY AND FUEL VALUE OF FOOD MATERIALS. 109 
far from 4,000 specimens of American food materials.* In estt- 
mating the proportion of nutrients in ordinary mixed diet, the 
results of 185 studies of actual dietaries were employed. These 
studies have been made in different parts of the United States, 
mostly within the past ten years; some by persons connected with 
this Station, but the larger number by other investigators engaged 
270 the cooperative inquiry under the auspices of the U.S. Depart- 
ment of Agriculture, of which the work here reported may be said 
to forma part. The coefficients of availability are based largely 
upon the results of digestion experiments with men. These belong 
to the cooperative inquiry just referred to, and a considerable num- 
ber were made by this Station. The data for heats of combustion 
have been compiled from various sources, and included results 
obtained in this laboratory. The factor for the heat of combustion 
of the unoxidized material of the urine ts based upon the results 
of the examination of 46 specimens of urine of healthy men with 
mixed diet. These results were mostly obtained in this laboratory 
in connection with digestion and metabolism experiments. 
The outcome of these estimates may be stated as follows: 
Taking tnto account (1) the heats of combustion of the protein 
compounds, fats and carbohydrates which occur tn different groups 
of food materials, and (2) the average proportion in which the 
different nutrients are furnished by different food materials in 
the ordinary mixed diet, the average heat of combustion of one 
gram of protein, fat and carbohydrates in such diet ts approxt- 
mately 5.65, 9.40 and 4.10 calories respectively. 
The results of a considerable number of digestion experiments 
with mixed diet give averages for coefficients of availability as 
follows: For protein 92 per cent., fats 95 per cent., and carbohy- 
drates 97 per cent. 
One gram of total protein of mixed diet burned in the body 
yields on the average not far from 4.0 calories, one gram of fat 
&.9 calories, and one gram of carbohydrates 4.0 calories of energy. 
The corresponding values per pound are 1,820, 4,240 and 1,820 
calories. One gram of available protein on the other hand has 
a fuel value of 4.4 calories, one gram of available fats 9.4 calo- 
ries, and one gram of available carbohydrates 4.1 calories. These 
values correspond to 2,000, 4,260 and 1,860 calories per gram. 

* See second foot-uote on p. I11. 
