What does the Respiratory Quotient (RQ) represent?

The Respiratory Quotient (RQ) represents the ratio of carbon dioxide produced during metabolism to the oxygen consumed. This measurement provides insight into the type of substrates being utilized for energy—whether carbohydrates or fats are being predominantly metabolized.

When carbohydrates are metabolized, they generally produce a higher amount of carbon dioxide relative to the amount of oxygen consumed, resulting in an RQ close to 1. In contrast, fat metabolism produces less carbon dioxide for the same amount of oxygen consumed, leading to an RQ around 0.7. Therefore, RQ is a critical indicator of metabolic shifts and substrate usage, reflecting how efficiently the body is converting various energy sources.

Understanding RQ is useful in fields such as exercise physiology and nutrition to assess metabolic responses during different activities and dietary conditions.