Final answer:
The first law of thermodynamics, also known as the conservation of energy principle, explains that the energy consumed by the body is transformed, used, or stored without any loss in the total amount of energy.
Step-by-step explanation:
The principle that describes how all energy taken into the body is accounted for and is either utilized directly, stored, or transformed into kinetic energy or heat is known as the first law of thermodynamics or the conservation of energy principle. In the context of living organisms, including the human body, this law asserts that the chemical energy from food is converted into work, thermal energy, and sometimes stored as chemical energy in fat. Whenever energy is transferred, whether it be through heat or work, the total amount of energy remains constant as it cannot be created or destroyed.
When considering how heat transfer is transformed into doing work, recognizing that not all energy conversion is 100% efficient is crucial due to the second law of thermodynamics. The first law essentially states that the change in internal energy of a system equals the net heat transfer into the system minus the net work done by the system. This balance underscores the body's role as an energy conversion machine, meticulously accounting for every joule of ingested energy.