Body temperature regulation refers to processes of heating and cooling that an organism uses to control its temperature. Thermoregulation is the ability of an organism to keep its body temperature within certain boundaries, even when the surrounding temperature is very different. This process is one aspect of homeostasis, a dynamic state of stability between an animal's internal environment and its external environment. The maintenance of body temperature in animals is a result of the process of metabolism, by which foodstuffs are converted into protein, carbohydrates, and fat, with the release of energy in the form of heat. Because active muscles metabolize food faster than muscles at rest, giving off more heat in the process, physical activity increases body temperature. This book provides a great variety of research on human as well as animal body temperature regulation. The principles of thermodynamics pertinent to the exchange of heat energy between the body and its surrounding environment is reviewed. Included also are studies on the effects of diet, body weight, exercise, disease, age and drugs.