A great deal of mechanism exists within the body in order to stabilise the internal environment, a process called homeostasis and this is particularly important with regard to body temperature. The temperature control centre becomes less able to respond to body temperature changes quickly and cannot always provide comprehensive heat regulation when environmental temperatures are above or below average for prolonged periods of time. For the body to balance the temperature, mechanisms must be in place to ensure that the heat gained is equal to the heat lost. Heat production is part of the energy obtained from the use of the high-energy molecule adenosine triphosphate (ATP). Enzymes within the mitochondrion produce ATP from the metabolism of glucose and fat. The glucose can be used as blood sugar to provide energy for cells, giving protein the same Atwater number as carbohydrates.