The production of heat and the expenditure of vital force necessarily involve the wear and breaking down of tissue. There is never an act, as the movement of a muscle; or a thought of the mind, but wears out many a living cell; and thus it is evident that unless continually repaired, the body machinery could last but a short time. But the One who made the machine, knowing this need, in infinite wisdom, prepared especially for it the particular kinds of food needed for repairing and building purposes. These are known as protein and mineral matters.
Protein is that element in our food which builds new tissues and repairs the worn parts of the body. It is found in milk, especially in the curd (the part utilized in cottage cheese) ; in the white of egg; in dried peas, beans, and lentils ; and in the various nuts, most of which are rich in protein. It is found in lesser quantities in all our common foods except sugar and pure fat; for instance, the gluten of wheat (that part which is gummy when chewed). Wheat gives us, in a loaf of good bread, about ten calories of protein in one hundred calories of food, which is the recognized dietary requirement in normal health.
Mineral Matters are those substances in our food which are used to build up the bones and the teeth, and which enter into the formation of the blood and the tissues; hence they are included in the building foods. They are found in small quantities in all natural foods, especially in whole grain cereals and fresh fruits and vegetables.