What has the greatest effect on a sedentary person's daily energy expenditure?

The primary determinant of a sedentary person's daily energy expenditure is their resting metabolic rate (RMR). RMR accounts for a significant portion of total daily energy expenditure, often around 60-75% in sedentary individuals. This rate refers to the energy expended by the body at rest to maintain essential physiological functions such as breathing, circulation, and cell production, which are crucial for sustaining life.

For a sedentary person, where physical activity levels are low, RMR fundamentally drives their energy needs. Factors influencing RMR include age, gender, weight, and body composition, with muscle mass being a key component. While physical activity and the thermic effect of food (the energy used to digest, absorb, and metabolize food) do play roles in energy expenditure, they are typically much lower in sedentary individuals compared to RMR. Hence, RMR remains the foremost contributor to their total energy expenditure.