What is metabolism? Metabolism is all the chemical and physical processes within the body. Basal metabolism is the sum of all the chemical activities of the cells necessary to sustain life. Basal metabolic needs can be quite large because we’re talking about sustaining the heart beating, the inhaling and exhaling of air, the maintenance of body temperature, and the sending of nerve and hormonal messages to direct all these activities. You may need 1,200 to 1,600 calories just to support your basal metabolism—this does not include all your other activities!