The carbon in the body is burned by being brought into contact with oxygen in the blood through exercise and full breathing, just as a fire is fanned to flame by bringing oxygen in contact with the fuel, by means of a draught of air. Keep all air away from a fire and it “dies out,” it has exhausted the oxygen and no heat is produced; keep all air from within the body, by cessation of breathing, and it also dies.
A room is heated with difficulty if the air in it does not contain sufficient oxygen. Just so the body which is not constantly supplied with pure air generates very little heat. The effect of oxygen in the creation of heat is practically demonstrated by voluntary, rapid, deep breathing, completely filling the lungs with air, while out in the cold. The body will become quickly warmed on the coldest day by this practice.
Ten to twelve deep breaths in succession “turn on the draught” inside and create combustion (heat), just as opening the draught to a stove by causing more air to circulate within it increases combustion or heat.
Remember that heat is the result of combustion—the more rapid the combustion in the body, caused by oxygen breathed in through the lungs, the greater the heat.
Just as much heat is created when fat is burned in the body as when it is burned outside of the body.
The heat from “burning” wood is produced by the union of the oxygen from the air with hydrogen and carbon, forming carbon dioxid and water.
The light in the burning of wood is caused by the rapid combustion. Combustion occurs within the body more slowly, hence no light is produced.
The exact process by which the potential energy latent in food is converted into heat and energy is not known. It is partly released during the digestive process, through the chemical action produced when the elements of the food come into contact with oxygen and with the digestive juices. This combustion gives to the digestive organs the necessary warmth to enable them to do effective work. A certain amount of heat is necessary for the chemical changes, and digestive juices flow more freely when the body is warm. Heat is necessary, also, to aid the peristaltic movements of the digestive organs.
It has been estimated that about one-sixth of the heat liberated evaporates through the skin, the lungs, and the excreta, while five-sixths is required to maintain the body heat.
If the digestive forces are not working perfectly and if the food is not properly prepared, some of the fuel is not utilized. But, in normal conditions, if the food is supplied in proportion to the energy required, the heat and energy given off should exactly equal the latent heat and energy consumed. If more food is taken than is necessary to produce heat and energy, the excess of material is stored and if the excess continues the bodily machinery may be clogged. The relief lies in consuming the excess through exercise. More oxygen is required to put the excess in condition for use, and the extra amount of oxygen is gained by means of the deep breathing occasioned by exercise.