In nutrition assessment, what does the term RQ stand for and what does it indicate?

• A. Respiratory quantity; indicates respiratory rate.
• B. Respiratory quotient; indicates oxygen consumption rate.
• C. Respiratory quality; indicates quality of breaths.
• D. Respiratory quotient; indicates the predominant substrate being metabolized (carbohydrate vs fat).

Answer: (D)

RQ stands for respiratory quotient. It is the ratio of carbon dioxide produced to oxygen consumed during metabolism (VCO2/VO2). This ratio reveals which macronutrient is fueling energy production. Oxidizing carbohydrates pushes the RQ toward 1.0, fat oxidation gives about 0.7, and protein oxidation is around 0.8–0.85. Therefore, the measured RQ indicates the predominant substrate being metabolized, which helps clinicians understand metabolic fuel use in nutrition assessment. It’s not the rate of oxygen use itself; that would be VO2. Keep in mind that RQ is derived from indirect calorimetry under steady-state conditions and can be influenced by nonmetabolic CO2 sources, so context matters for interpretation.