[Illustration: FIG. 27.--_a_ is the amount of fat necessary to make
one calorie; _b_ is the amount of sugar or proteid necessary to make
one calorie.]
63. The Proteids. The proteids are the building foods, furnishing
muscle, bone, skin cells, etc., and supplying blood and other bodily
fluids. The best-known proteids are white of egg, curd of milk, and
lean of fish and meat; peas and beans have an abundant supply of this
substance, and nuts are rich in it. Most of our proteids are of animal
origin, but some protein material is also found in the vegetable
world. This class of foods contains carbon, oxygen, and hydrogen, and
in addition, two substances not found in carbohydrates or
fats--namely, sulphur and nitrogen. Proteids always contain nitrogen,
and hence they are frequently spoken of as nitrogenous foods. Since
the proteids contain all the elements found in the two other classes
of foods, they are able to contribute, if necessary, to the store of
bodily energy; but their main function is upbuilding, and the diet
should be chosen so that the proteids do not have a double task.
|