Indirect calorimetry (IC) calculates

• A. Total energy expenditure
• B. Nitrogen balance
• C. Heat released from the subject
• D. Resting energy expenditure REE and respiratory quotient RQ

Answer: (D)

Indirect calorimetry works by tracking gas exchange—oxygen you consume and carbon dioxide you produce. From these measurements you can derive how much energy the body is expending at rest and what fuels are being burned. The resting energy expenditure is the calories used at rest, while the respiratory quotient—the ratio of CO2 produced to O2 consumed—indicates the mix of substrates being oxidized (carbs vs fats). These two outputs are exactly what indirect calorimetry provides, making them the best answer. Nitrogen balance requires measuring nitrogen intake and losses, not gas exchange, and heat output isn’t measured directly by this method either (energy expenditure can be used to estimate total needs with extra factors, but IC itself yields REE and RQ).