If an individual produces 1 L of carbon dioxide for 1 liter of oxygen consumed, what will there RER be?
The correct answer and explanation is:
Correct Answer: 1.0
Explanation (Respiratory Exchange Ratio – RER)
The Respiratory Exchange Ratio (RER) is a measure used in physiology to determine the predominant type of fuel (carbohydrates or fats) being used for energy during metabolism. It is calculated using the formula: RER=VCO2VO2\text{RER} = \frac{\text{VCO}_2}{\text{VO}_2}
Where:
- VCO₂ = volume of carbon dioxide produced
- VO₂ = volume of oxygen consumed
In the given scenario:
- VCO₂ = 1 L
- VO₂ = 1 L
So: RER=11=1.0\text{RER} = \frac{1}{1} = 1.0
Interpretation of RER = 1.0
An RER value of 1.0 typically indicates that the body is metabolizing pure carbohydrates for energy. Here’s why:
- When carbohydrates (like glucose) are oxidized, the amount of CO₂ produced is equal to the amount of O₂ consumed. For example: C6H12O6+6O2→6CO2+6H2O\text{C}_6\text{H}_{12}\text{O}_6 + 6O_2 \rightarrow 6CO_2 + 6H_2O In this reaction, 6 moles of CO₂ are produced for every 6 moles of O₂ consumed — giving an RER of 1.0.
- On the other hand, if fat were the main fuel source, less CO₂ is produced per unit of O₂ consumed, resulting in a lower RER, around 0.7.
Applications
Understanding RER is crucial in:
- Exercise physiology: To determine how the body is fueling physical activity.
- Metabolic testing: For assessing metabolic rate and substrate utilization.
- Clinical settings: To monitor critically ill patients or those with respiratory or metabolic disorders.
Conclusion
When an individual produces 1 liter of carbon dioxide for every 1 liter of oxygen consumed, their RER is 1.0, indicating predominant carbohydrate metabolism.