The term energy metabolism indicating phisiologics those processes that allow the body to transform food into various forms of energy necessary for the survival of the human being and the performance of activities of daily living.

Through our body energy metabolism chemical energy derived from metabolism of nutrients, derived from the same nutrients as proteins, nucleic acids, lipids, polysaccharides and other substances, form molecules necessary for cellular functions of our body.

The energy produced and consumed by the organism is measured in kilocalories; the amount of heat required to raise the temperature of one gram of water by one degree (exactly one gram of distilled water. Pressure of 1 atmosphere with temperature which must climb from 14.5 to 15.5 degrees). We have already seen how all the food, once ingested, they are broken down to their dietary principles, only to be absorbed. Glycidol, protein and fat are the basic elements of all the foods we eat; transformation into energy produces, for each gram of principle, 4 kilocalories in the case of glycidol, 9 kilocalories in the case of lipids and 4 kilocalories in the case of proteins.