(1) to build and maintain the cell until its work is done;
(2) to furnish the heat necessary to decompose the food into its elements, and to produce the energy by which all the body processes are carried on.
Food Elements
That the food may be appropriated by the body it must be not only proper in kind and quantity, but the body must also be in condition to digest, absorb, and assimilate it and to eliminate the waste, otherwise the body needs are not met.
It is the nourishment which the body assimilates and appropriates to its needs which counts in food economy, not necessarily the amount consumed.
Therefore if the food is to economically serve its purpose, the body must be in a condition to digest and assimilate it—this condition depends largely on perfect circulation, correct position of organs, and correct breathing habits.
Of the fifteen to twenty substances contained in foods and comprised in the body, the principal ones are oxygen, hydrogen, carbon, nitrogen, chlorin, sodium, potassium, magnesium, iron, calcium, phosphorus, and sulphur. The differences in the forms of matter lie in the proportions in which these elements are combined.
Those containing the largest proportion of nitrogen are called Nitrogenous foods or Protein—such as meat, eggs, and some vegetables.
Those containing the largest proportion of carbon are known as Carbonaceous—such as cereals, sugar, and fat.
The four food elements, indispensable to life, either of plant or animal, are oxygen, hydrogen, carbon and nitrogen.