Which RER value indicates fat oxidation predominates?

Which RER value indicates fat oxidation predominates?

• A. 1.0
• B. 0.85
• C. 0.7
• D. Greater than 1

Answer: (C)

RER shows which fuel is being oxidized by comparing carbon dioxide produced to oxygen consumed. Fat oxidation sits around 0.7, so a value near 0.7 indicates fat is the predominant fuel. Carbohydrate oxidation pushes RER toward 1.0, and values above 1 can occur with very intense exercise due to buffering and non-metabolic CO2 release. Since fat yields less CO2 per unit of O2 consumed, the lower ratio (0.7) reflects fat being used more than carbohydrates.

RER shows which fuel is being oxidized by comparing carbon dioxide produced to oxygen consumed. Fat oxidation sits around 0.7, so a value near 0.7 indicates fat is the predominant fuel. Carbohydrate oxidation pushes RER toward 1.0, and values above 1 can occur with very intense exercise due to buffering and non-metabolic CO2 release. Since fat yields less CO2 per unit of O2 consumed, the lower ratio (0.7) reflects fat being used more than carbohydrates.