What is necessary for infused nutrients prior to indirect calorimetry measurement?

• A. The rate and composition of nutrients being infused on a continuous basis should be stable for at least 12 hours for an accurate study
• B. The rate should be changed during the measurement
• C. Nutrients infusion has no effect
• D. Infusions should be stopped during measurement

Answer: (A)

Indirect calorimetry relies on a stable metabolic state so that gas exchange reflects true energy expenditure, not transient responses to feeding. If the rate or composition of infused nutrients is changing, the body shifts substrate utilization and CO2 production, which alters VO2, VCO2, and the respiratory quotient. Holding the infusion rate and macronutrient makeup constant for at least 12 hours before measurement lets the body's metabolism reach a steady state, yielding accurate and consistent readings. Changing the rate during measurement or stopping infusions would disrupt this steadiness and bias the results, while saying infusions have no effect ignores how substrate delivery shapes oxidation and gas exchange.