From the Guidelines
A respiratory quotient of 1.2 indicates lipogenesis, as it suggests that the body is utilizing carbohydrates as the primary source of fuel and converting excess carbohydrates to fat for storage. The respiratory quotient is the ratio of carbon dioxide produced to oxygen consumed during metabolism, and an RQ value greater than 1.0 indicates that more carbon dioxide is being produced than oxygen is being consumed, which is consistent with lipogenesis 1.
Metabolic Pathways and RQ Values
- Pure carbohydrate metabolism yields an RQ of 1.0
- Fat metabolism yields an RQ of about 0.7
- Protein metabolism yields an RQ of approximately 0.8
- An RQ value of 1.2 is indicative of lipogenesis, where excess carbohydrates are being converted to fat for storage 1.
Clinical Implications
Understanding the RQ value helps identify which metabolic pathways are predominant in the body at a given time, and this information can be used to guide nutritional therapy and optimize energy expenditure in critically ill patients 1. The use of indirect calorimetry to measure RQ and energy expenditure can help prevent overfeeding and underfeeding, and improve clinical outcomes in ICU patients.
From the Research
Respiratory Quotient Analysis
- A respiratory quotient (RQ) of 1.2 indicates that the body is utilizing a significant amount of carbohydrates as a source of fuel 2.
- RQ values greater than 1.0 suggest net fat synthesis, which is often associated with lipogenesis 2.
- An RQ of 1.2 is higher than the typical RQ values for fat utilization (around 0.7-0.8) and protein utilization (around 0.8-0.9), but lower than the RQ value for pure carbohydrate utilization (around 1.0) 3, 4.
- The given RQ value of 1.2 is closest to the RQ value for carbohydrates, suggesting that carbohydrates are the primary source of fuel.
Fuel Utilization
- Carbohydrates are the source of fuel when the RQ is close to 1.0, as they produce more CO2 per O2 consumed compared to fat 5, 6.
- An RQ of 1.2 suggests that the body is utilizing more carbohydrates than fat or protein as a source of fuel.
- This is consistent with the idea that a high RQ value indicates a higher reliance on carbohydrates for energy production.
Answer
- Based on the analysis, the correct answer is (d) carbohydrates are the source of fuel.