SO STORRS AGRICULTURAL EXPERIMENT STATION. 
muscular work: Unlike the proteids they cannot form nitrog- 
enous tissue, though they are contained and stored in the fluids 
and tissues of the body. Thus large amounts of fat are stored 
in adipose or fatty tissue where it forms a reserve supply of 
fuel for future use. Both the fats and the carbohydrates, 
by being themselves consumed, spare the more essential and 
costly nitrogenous matter of food and body tissue from con- 
sumption. 
PROPORTIONS OF NUTRIENTS SUPPLIED BY DIFFERENT 
GROUPS OF FOOD MATERIALS IN THE 
AVERAGE DIET. 
In discussing the availability and fuel value of the nutrients 
of food we have to consider not simply the individual food 
materials or the groups into which the food materials may be 
classified, but also the proportions of these individual materials 
and groups in the average diet. What we wish to get at is the 
nutritive value of each kind of food as it is actually eaten as 
part of a mixed diet. Thus in certain digestion experiments 
milk has been found to be more completely digested and thus 
more fully utilized when it is taken with bread than when it 
formed the sole diet. Furthermore different food materials or 
nutrients of different food materials differ considerably in di- 
gestibility and availability even when the conditions for utiliz- 
ing them are most favorable. If we wish to obtain figures for 
the average availability and fuel value of protein, fats and 
carbohydrates of ordinary diet we must know not only the 
availability and fuel value of each of the different kinds or 
classes of food materials, but also the proportion in which 
these occur in the diet and the proportions of the total protein, 
fats and carbohydrates that are obtained from each. ‘These 
can be learned only by careful examination of a large number 
of dietary studies. Fortunately the results of some 250 such 
studies carried on in this country are now on record. Of these 
185 seem to the writers to be of such character as to warrant 
including them in making general estimates of the proportions 
of the different kinds or groups of food materials in the 
average diet and the proportional amounts of the different 
nutrients furnished by each group in the whole diet. 

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