Respiratory quotient (RQ) of pure fat oxidation is 0.7. This is because:

• A Fatty acid oxidation produces only CO2 and no water
• B Fatty acids have a lower proportion of oxygen relative to carbon and hydrogen compared with carbohydrates, requiring more O2 per CO2 produced ✓
• C RQ of fat is 0.7 because fatty acids enter the TCA cycle as succinyl-CoA
• D Beta-oxidation of fatty acids consumes GTP rather than ATP, reducing CO2 output

Explanation

RQ = moles CO2 produced / moles O2 consumed. Fatty acids are highly reduced (low O:C ratio) compared with carbohydrates; complete oxidation of a fatty acid like palmitate (C16H32O2) requires far more O2 relative to the CO2 produced, giving RQ = 0.70. Carbohydrates (empirical formula CH2O) have RQ = 1.0 because they are already partially oxidised. Protein has RQ ≈ 0.8. A mixed diet RQ ≈ 0.85.

Reference: Harper's Illustrated Biochemistry, 32nd ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.