Nitrogenous Foodstuffs or Proteins
The proteins form heat and energy when the supply of sugars, starches, and fat are exhausted, but proteins, alone form muscle, bone and sinew. They are, in this sense, the most important of foods,—they are, also, the most costly.
The foods most rich in proteins are meat and eggs. These have undergone chemical changes from the vegetable kingdom being built up into more complex compounds in the animal kingdom.
Meat and eggs are the tissue builders. In this connection it may be well to state that blood is tissue; thus meat and eggs build the blood, as well as muscle and sinew.
Nitrogenous foods, or proteins, are so called because of the large proportion of nitrogen which they contain. All nitrogenous foods contain considerable carbon—mostly in the form of fat in the meat elements—but the carbonaceous foods contain so little of the proteins that they do not appreciably enter into the nutrition,—the carbon and nitrogen in the carbo-nitrogenous foods are more equally divided.
The nitrogenous or protein elements in the body constitute about one-fifth of its weight. They make the framework, forming the basis of blood, lymph, muscle, sinew, bone, skin, cartilage, and other tissues.
Worn out body tissues is constantly being torn down and eliminated and the protein in the foods must daily furnish material for repair, as well as for building new tissue in the growing child.
A young animal’s first need is for growth, not having learned to exercise sufficiently to use much energy, and the first food given is an animal product—milk tobabes and other mammals, while the young of other animals are first fed upon eggs.
The nitrogenous foods are required in smaller bulk than vegetables and fruits; they are more concentrated and contain less waste. According to recent experiments, the average adult requires from two to four ounces a day of nitrogenous foods, to repair the waste, according to the proportion of nitrogen contained. Happily, where more is consumed, the system has the power, up to a certain limit (depending upon the physical condition and the daily activity), to eliminate an excess. It is needless to say that if the daily waste is not re-supplied, the digestion and bodily nutrition suffer. The systemmusthave the two to four ounces to supply the nitrogen daily excreted, or the tissues themselves will be consumed.
The proteins, of which meat is the principal one, are classified as
Albuminoids:—albumin (white of eggs), casein (curd of milk), myosin (the basis of lean meat and gluten of wheat),
Gelatinoids, (connective tissue of meat),
Extractives (appetizing and flavoring elements).