820 REPORT OF COMMISSIONER OF FISH AND FISHERIES. 
in the body is to make blood, and to build up the muscle, tendon, bone, 
and other tissues which constitute the framework of the body and 
repair them, as they are being continually worn out by use. Brain and 
nerve are also formed to a considerable extent from the protein com- 
pounds of the food. The protein of the food is also formed into fat in 
the body, and serves as fuel to supply it with heat and muscle energy. 
The fats of the food are stored as fat in the body, and may be trans- 
formed into carbohydrates, but their chief use is for fuel. The carbo- 
hydrates are transformed into fat in the body, and may be stored as body 
fat, but their chief use is for fuel. The mineral matters make bone and 
have various other uses in the body. 
When we eat meat, its protein serves to make blood, bone, muscle, 
tendon, brain, and nerve. We can also use it to make fat, and it is con- 
sumed — i. e., burned as fuel to yield its heat to keep our bodies warm 
and give muscular strength for work. The fat of the meat can not do 
the work of the protein in forming muscle, tendon, and the like, but is 
much more valuable than protein for fuel. Bread supplies us with pro- 
tein and fat, and also with carbohydrates in the form of starch, dex- 
trin, and sugar. The protein and fats serve the same purposes as those 
of meat. The carbohydrates which make up the bulk of the nutritive 
material of bread and potatoes, and of which only minutest quantities 
occur in meat, are valuable chiefly as fuel, though they also yield fat. 
To recapitulate: The nutritive material of very lean meat and the 
leaner kinds of fish consists almost entirely of protein. Tallow, lard, 
oils, and butter are fats. Sugar and starch are carbohydrates. All the 
different food materials contain mineral matters. Animal foods supply 
chiefly protein and fats. Most vegetable foods contain but little of these, 
their nutrients being chiefly carbohydrates. Beans, pease, and other 
leguminous plants, however, supply considerable quantities of protein. 
Milk differs from most other animal foods in that it has large quantities 
of a carbohydrate, “ milk-sugar.” Oysters approach milk in composition. 
For nourishment we need all of the different classes of nutrients and 
in proper proportions. Thus a day’s food for an average man doing 
moderately hard muscular work may appropriately supply, on the 
average, about 4J ounces of protein, the same quantity of fats, and 16 
ounces of carbohydrates. 
The cheapest food is that which supplies the most nutritive material 
for the least money ; the most economical food is that which is cheap- 
est and best adapted to the wants of the user. 
From the standpoint of their uses in the nutrition of man, the con- 
stituents of ordinary foods may be succinctly classified as follows: 
Edible substance , as the flesh of meats and fish, the shell contents of 
oysters, wheat flour. 
Refuse, as bones of meat and fish, the shells of oysters, bran of 
wheat. 
