"There can be no doubt that, whatever other function food may or may not have, it replaces broken-down tissue. The tissue-wastes of the preceding day are replenished by the food eaten; so the body remains about the same in weight, no matter how much exercise be taken, or how much tissue is broken down. These tissues are very complex in their nature, and a variety of food is consequently necessary to restore the tissues destroyed-food containing a number of elements (the counterpart of the elements destroyed), being necessary to offset the waste. Proteid, fats, carbohydrates, and various salts are, therefore, necessary in the food; and no food that does not contain these constituents, in larger or smaller quantities, can be used by the body, or can be classed as a true "food." " - Hereward Carrington