64 POODS AND NUTRITION 



nized to be a valuable tissue builder. Potatoes with their 

 abundant starch are in the same way put down as fuel or 

 energy producers. If we consider our own experience, 

 however, we realize that composition tells us only a little 

 of the true value of a food. A food, for example, may 

 contain all the nutrients necessary to the body, and yet 

 be absolutely valueless to us. Hay, for instance, contains 

 all the nutrients necessary to support life, and yet man 

 cannot use it as food. Again, certain foods may be so 

 rare that their cost prohibits their use. In general, then, 

 we may say that the value of a food is determined only 

 when we have considered its composition, its fitness for 

 our use, and its cost. 



The first point that may be noted from Chart II. is 

 that most food as bought in the market is made up of 

 nutrient only in part. The remainder may consist of 

 bone, connective tissue, skin, bran, etc., all of which is 

 included under the heading of refuse in the chart. 

 The amount of refuse present is evidently an important 

 factor as regards the value of a food. It is because of 

 the fact that eggs, milk, and bread contain almost no 

 refuse that they are such valuable foods. 



A second point to be noted is the water content of 

 foods. In this respect, animal foods, in general, contain 

 more water than the vegetable foods. Exceptions to- this 

 rule are found in potatoes, onions, lettuce, and some other 

 vegetables, in which the proportion of water is very high. 

 In meat foods, too, the fatty forms contain less water 

 than the lean meats. In general, other things being 

 equal, the higher the proportion of water the less the food 

 value. Fish on this account are less valuable as food than 

 ordinary meats. 



