What fraction of total energy expenditure is used to maintain body temperature?

The fraction of total energy expenditure used to maintain body temperature is indeed approximately 2/3 of total energy expenditure. This is primarily due to the necessary thermoregulatory processes the body undergoes to maintain a stable internal temperature, a vital aspect of homeostasis.

When the body temperature fluctuates due to external conditions or physical activity, the body needs to expend energy to either produce heat (through mechanisms like shivering) or dissipate heat (through sweating or increasing blood flow to the skin). This thermogenic process is critical for sustaining proper physiological function.

Additionally, various factors can influence this energy expenditure, such as ambient temperature, metabolism, and the physical state of the individual. However, in general terms, the energy required to keep the body at a constant temperature constitutes a significant portion of total energy expenditure, reflecting its importance in overall metabolism.