Resting energy expenditure (REE) is primarily influenced by which factor?

Resting energy expenditure (REE) is primarily influenced by lean body mass because muscle tissue requires more energy to maintain than fat tissue. This means that individuals with a higher amount of lean body mass will typically have a higher resting energy expenditure, as their bodies require more calories at rest to support the metabolic processes associated with muscle maintenance and operation.

While age and gender can also influence REE, the degree of impact is often less pronounced than that of lean body mass. For instance, metabolic rate tends to decrease with age due to a loss of lean tissue and hormonal changes. Gender differences also play a role, as men generally have a higher percentage of muscle mass than women, contributing to their typically higher REE. Hydration levels, while important for overall health and metabolic functioning, do not directly influence the basal metabolic rate as significantly as the composition of body mass does. Therefore, lean body mass stands out as the most critical factor affecting resting energy expenditure.