Does indirect calorimetry measure nitrogen balance?

• A. Yes
• B. No
• C. Sometimes
• D. Not applicable

Answer: (B)

The main idea is that indirect calorimetry focuses on energy expenditure and substrate use by measuring gas exchange, not nitrogen losses. By tracking oxygen consumption and carbon dioxide production, it provides total energy needs and the respiratory quotient, which tells you which fuels are being burned. Nitrogen balance, on the other hand, requires knowing how much nitrogen you take in (through protein) and how much you excrete (mainly in urine as urea, with some loss in feces). That measurement isn’t provided by indirect calorimetry, so it cannot determine nitrogen balance directly. In practice, you use indirect calorimetry to tailor energy provision while assessing protein status separately via intake and urinary (and sometimes fecal) nitrogen measurements.