4 BULLETIN 469, U. S. DEPARTMENT OF AGRICULTURE. 
meat, which is the chief article of diet. Though it seems to be less 
well known, it is nevertheless true, that fats are also eaten in consid- 
erable quantity in tropical countries, as is evident when one recalls 
the coconut oil of the South Sea Islands and the olive oil and other 
fats so much used in cookery in other regions characterized by a very 
warm climate. As everyone knows, dwellers in temperate regions use 
fat in the diet in many ways, which are determined largely by the pre- 
vailing food habits and the kinds of fat procurable, and in quantities 
which bear a more or less direct relation to the amount of physical work 
performed. Men engaged in severe work out-of-doors often eat large 
quantities of fatty foods. Workmen in lumber camps, for instance, 
relish a diet of pork and beans and other fat foods which would be 
too hearty for the office worker or clerk. It is difficult to obtain any 
definite figures for the quantity of fat eaten by the average person, 
but in 1,300 dietary studies of families, carried out among different 
races and in different countries, it was found that the average quan- 
tity of fat eaten was about 4J ounces per person per day, the varia- 
tion recorded being from 1J to 13 ounces per person per day. 
While fats and carbohydrates may replace each other to a consid- 
erable extent, recent investigations indicate that some carbohydrate 
supplied by the food or formed in the body from protein is essential 
for the combustion of fats in the body. Experts in nutrition and 
dietetics, therefore, believe that neither one should be used to the 
exclusion of the other. 
DIGESTIBILITY OF FATS. 
While all fats yield approximately equal amounts of energy when 
burned outside of the body, the energy which the body actually de- 
rives from each is dependent upon its digestibility ; that is. the pro- 
portion which the body retains. The digestibility of a number 
of the individual fats 1 has been determined, and the information 
at present available indicates that fats in general are very thoroughly 
digested: more so, indeed, than the animal or vegetable proteins 
and the starch occurring in the ordinary mixed diet. Such 
slight differences as have been observed in the digestibility of in- 
dividual fats evidently correspond to differences in their melting 
points. Available evidence indicates that fats such as mutton fat. 
having a melting point higher than the body temperature, are less 
completely assimilated than those melting at a lower temperature, 
such as lard, butter, olive oil, and cottonseed oil. Also, it has been 
shown by feeding experiments with laboratory animals that animal 
and vegetable stearins (melting above body temperature) are only 
1 U. S. Dept. Agr. Bui. 310 (1915). 
