The respiratory quotient (RQ) is a measure of the ratio of carbon dioxide production to oxygen consumption during metabolism. It provides insight into the body's primary fuel source, whether it's carbohydrates, fats, or proteins. The RQ value can vary depending on several factors:

1. Diet:

  • Carbohydrates: When consuming primarily carbohydrates, the RQ is close to 1.0 because the body efficiently converts carbohydrates into energy, producing equal amounts of carbon dioxide and oxygen.
  • Fats: A diet high in fats results in an RQ below 1.0 because fats produce less carbon dioxide and more oxygen during metabolism.
  • Proteins: A protein-rich diet can lead to an RQ slightly above 1.0 due to the production of carbon dioxide from protein metabolism.

2. Exercise Intensity:

  • Resting State: At rest, the RQ is typically around 0.85, indicating a mix of carbohydrate and fat utilization.
  • Moderate Exercise: During moderate-intensity exercise, the RQ increases towards 1.0 as the body shifts to carbohydrate metabolism for quick energy.
  • High-Intensity Exercise: In high-intensity workouts, the RQ can exceed 1.0, suggesting a reliance on anaerobic metabolism, where glucose is broken down without oxygen.

3. Fasting and Starvation:

  • Fasting: Prolonged fasting or starvation can cause the RQ to decrease below 0.7 as the body switches to fat metabolism for energy, producing ketones.
  • Refeeding: After a period of fasting, the RQ can temporarily increase above 1.0 during the refeeding phase as the body replenishes glycogen stores.

4. Metabolic Conditions:

  • Diabetes: In uncontrolled diabetes, the RQ can be elevated due to the body's inability to use glucose effectively, resulting in increased fat metabolism.
  • Thyroid Disorders: Thyroid hormone imbalances can affect RQ, with hyperthyroidism leading to an increased RQ and hypothyroidism causing a decreased RQ.

5. Drugs and Medications:

  • Stimulants: Some medications, such as caffeine and ephedrine, can increase the RQ by stimulating the body's metabolism and promoting fat oxidation.
  • Sedatives: Conversely, sedatives and tranquilizers can lower the RQ by reducing metabolic rate and shifting the body towards carbohydrate metabolism.

6. Environmental Factors:

  • Temperature: In cold environments, the RQ can increase as the body burns more energy to maintain body temperature.
  • Altitude: At high altitudes, the RQ may decrease due to the body's adaptation to lower oxygen levels, favoring fat metabolism.

In summary, the RQ is a valuable tool for assessing metabolic processes and fuel utilization in the body. It can vary depending on diet, exercise intensity, fasting, metabolic conditions, medications, and environmental factors. Understanding these factors can help optimize nutrition, exercise strategies, and medical treatments based on individual needs.


1. Can RQ be used to track weight loss?
Answer: Yes, RQ can provide insights into weight loss by indicating the body's primary fuel source. A consistently low RQ may suggest efficient fat utilization, while a high RQ might indicate a need to adjust macronutrient intake.

2. What is a normal RQ range?
Answer: In healthy individuals, the RQ typically falls between 0.85 and 1.0 during rest and moderate exercise. It can temporarily exceed 1.0 during high-intensity exercise or after fasting.

3. How does RQ relate to ketosis?
Answer: A sustained RQ below 0.7 often indicates ketosis, a metabolic state where the body burns fat as its primary fuel source.

4. Can RQ be influenced by hydration status?
Answer: Yes, dehydration can lead to an artificially elevated RQ as the body conserves water by producing less urine, resulting in a higher concentration of carbon dioxide in the breath.

5. Is RQ affected by sleep?
Answer: During sleep, the RQ is typically lower due to reduced metabolic activity and a shift towards fat metabolism. However, REM sleep can cause brief increases in RQ as the brain becomes more active.



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