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The Respiratory Quotient (RQ) Calculator determines the ratio of carbon dioxide produced to oxygen consumed during metabolism. RQ is a dimensionless number that reveals which macronutrient substrate the body or organism is predominantly oxidizing for energy. Pure carbohydrate oxidation gives RQ = 1.0, pure fat oxidation gives RQ = 0.7, and protein oxidation gives approximately RQ = 0.8.
This measurement is fundamental in exercise physiology, clinical nutrition, and metabolic research. RQ values help determine energy expenditure, guide nutritional support in clinical settings, and assess metabolic flexibility in health and disease.
The respiratory quotient is a simple ratio:
RQ = CO₂ Produced / O₂ Consumed
Reference RQ values for pure substrates are:
Carbohydrates: RQ = 1.0 (C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O)
Fats: RQ = 0.7 (more O₂ needed per CO₂ produced)
Proteins: RQ = 0.8 (intermediate value)
Mixed diets typically yield RQ values between 0.8 and 0.85.
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An RQ of 0.8 indicates a mix of substrates being oxidized, consistent with typical resting metabolism on a mixed diet containing both carbohydrates and fats.
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An RQ near 1.0 indicates predominant carbohydrate oxidation, as might occur during high-intensity exercise or after a carbohydrate-rich meal.
Yes, RQ values above 1.0 indicate lipogenesis, the conversion of carbohydrates to fat. This occurs when carbohydrate intake exceeds energy needs, and the excess is stored as fat. Values above 1.0 also occur during hyperventilation, though this reflects respiratory rather than metabolic changes.
RQ is measured using indirect calorimetry, where a person breathes into a metabolic cart that precisely measures the volumes of O₂ consumed and CO₂ produced. The measurement is typically performed in a resting, fasted state for BMR assessment, or during exercise for metabolic profiling.
A chronically low RQ (around 0.7) at rest suggests heavy reliance on fat oxidation, which may be seen in uncontrolled diabetes, starvation, or very low-carbohydrate diets. In clinical settings, an RQ below 0.7 may indicate ketosis. Metabolic flexibility, the ability to shift between substrates, is a marker of metabolic health.
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