Which of the following makes the GREATEST contribution to total energy expenditure?

• A. Resting metabolic rate
• B. Physical activity energy expenditure
• C. Thermic effect of food
• D. Resting blood sugar levels

Answer: (A)

Total energy expenditure comes from three main parts: the energy used for basic bodily functions at rest, the energy required to digest and process the food you eat, and the energy spent during physical activity. Resting metabolic rate is the largest portion, typically making up about 60-75% of daily energy use. It reflects the energy needed to keep organs like the brain, heart, liver, and kidneys functioning and to maintain essential processes, and it scales with lean body mass, which tends to be relatively stable day to day.

The thermic effect of food contributes about 5-10% of daily energy expenditure, as energy is expended to digest, absorb, and assimilate nutrients. Physical activity energy expenditure varies widely with how active you are; it can be substantial, especially in highly active individuals, but on average it is smaller than resting metabolic rate.

Resting blood sugar levels do not constitute a separate, major component of energy expenditure; maintaining glucose in the bloodstream is part of metabolic regulation, not a distinct energy cost like RMR, TEF, or PAEE.

So the greatest contribution to total energy expenditure comes from resting metabolic rate.