What is the respiratory exchange ratio (RER) defined as?

What is the respiratory exchange ratio (RER) defined as?

• A. The ratio of carbon dioxide produced to oxygen consumed
• B. The ratio of oxygen consumed to carbon dioxide produced
• C. The rate of oxygen consumption
• D. The amount of ventilation per minute

Answer: (A)

RER shows which fuel the body is burning by looking at the gases you exchange. It is defined as the amount of carbon dioxide produced per minute divided by the amount of oxygen consumed per minute (VCO2/VO2). This ratio shifts with substrate use: around 0.7 indicates fat oxidation, about 1.0 indicates carbohydrate oxidation, and it can rise above 1.0 during intense exercise due to buffering of lactic acid. It’s a measure from gas exchange, not a direct measure of ventilation or VO2 alone.

RER shows which fuel the body is burning by looking at the gases you exchange. It is defined as the amount of carbon dioxide produced per minute divided by the amount of oxygen consumed per minute (VCO2/VO2). This ratio shifts with substrate use: around 0.7 indicates fat oxidation, about 1.0 indicates carbohydrate oxidation, and it can rise above 1.0 during intense exercise due to buffering of lactic acid. It’s a measure from gas exchange, not a direct measure of ventilation or VO2 alone.