According to Georgia State University, metabolic processes produce heat by liberating the energy stored in food sources. Just as a fire produces heat by releasing some of the energy contained in the chemical bonds of the fuel, humans and other animals free the energy found in the chemical bonds of the foods they consume. Metabolic processes operate much slower than fire, so fire-like temperatures are not reached.
Georgia State University explains that humans are not able to use all of the energy they release from food. About half of the energy in a food item is converted into the energy currency of the body, called adenosine triphosphate, or ATP. The other half of the energy is used to maintain the relatively high temperature of the body, while the remainder is radiated away. Over the course of about 24 hours, humans release the same amount of energy produced by a 100-watt light bulb.
Georgia State University states that there are two parts of metabolism. The first, called catabolism, involves breaking down molecules like glucose and carbohydrates to release the energy inside them. The second component of metabolism is called anabolism. Anabolism is a constructive process, in which the body produces muscles and other structures.