59. Why we eat so Much. The cells of the body are constantly, day by
day, minute by minute, breaking down and needing repair, are
constantly requiring replacement by new cells, and, in the case of the
child, are continually increasing in number. The repair of an ordinary
machine, an engine, for example, is made at the expense of money, but
the repair and replacement of our human cell machinery are
accomplished at the expense of food. More than one third of all the
food we eat goes to maintain the body cells, and to keep them in good
order. It is for this reason that we consume a large quantity of food.
If all the food we eat were utilized for energy, the housewife could
cook less, and the housefather could save money on grocer's and
butcher's bills. If you put a ton of coal in an engine, its available
energy is used to run the engine, but if the engine were like the
human body, one third of the ton would be used up by the engine in
keeping walls, shafts, wheels, belts, etc., in order, and only two
thirds would go towards running the engine. When an engine is not
working, fuel is not consumed, but the body requires food for mere
existence, regardless of whether it does active work or not. When we
work, the cells break down more quickly, and the repair is greater
than when we are at rest, and hence there is need of a larger amount
of food; but whether we work or not, food is necessary.

60. The Different Foods. The body is very exacting in its demands,
requiring certain definite foods for the formation and maintenance of
its cells, and other foods, equally definite, but of different
character, for heat; our diet therefore must contain foods of high
fuel value, and likewise foods of cell-forming power.

Although the foods which we eat are of widely different character,
such as fruits, vegetables, cereals, oils, meats, eggs, milk, cheese,