Respiratory Quotient

The respiratory quotient (RQ) compares how much carbon dioxide an organism releases to how much oxygen it uses during respiration. It works because different nutrients are broken down with different chemical balances: fats generally need more oxygen to be oxidized and produce relatively less CO2, while carbohydrates tend to produce CO2 and use O2 in nearly equal amounts. So the RQ gives a useful clue about which type of fuel is being metabolised and how metabolism changes with diet, exercise, or starvation.

Use RQ when interpreting metabolic fuel use in physiology, exercise science, or respirometry experiments. It is especially helpful for comparing whether cells are mainly burning carbohydrates, fats, or proteins under different conditions.

• Reversing the ratio and calculating O2/CO2 instead of CO2/O2
• Assuming one RQ value proves a single fuel is being used exclusively
• Using the formula without matching the same time interval and units for both gases