What is the respiratory quotient for a carbohydrate meal

**Core Concept**
The respiratory quotient (RQ) is a measure of the ratio of carbon dioxide (CO2) produced to oxygen (O2) consumed by the body during metabolism. It varies depending on the type of fuel being metabolized, providing insight into the body's energy expenditure and substrate utilization.

**Why the Correct Answer is Right**
When a carbohydrate meal is consumed, it is broken down into glucose, which is then metabolized through glycolysis, producing pyruvate. Pyruvate is converted into acetyl-CoA, which enters the citric acid cycle, producing CO2 and ATP. Since carbohydrates are the primary source of energy, the RQ for a carbohydrate meal is approximately 1.0, indicating that for every molecule of O2 consumed, one molecule of CO2 is produced.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because a protein-rich meal has an RQ of approximately 0.8, not 1.0. This is because proteins are metabolized through deamination, producing CO2 and ammonia, which is then converted to urea.
**Option B:** This option is incorrect because a fat-rich meal has an RQ of approximately 0.7, not 1.0. This is because fats are metabolized through beta-oxidation, producing acetyl-CoA, which enters the citric acid cycle and produces less CO2 than carbohydrates.
**Option C:** This option is incorrect because an RQ of 1.5 is not a typical value for any type of meal. This value would indicate a significant imbalance in CO2 and O2 production.

**Clinical Pearl / High-Yield Fact**
The respiratory quotient can be used to estimate the body's substrate utilization, with an RQ of 1.0 indicating carbohydrate metabolism, 0.8 indicating protein metabolism, and 0.7 indicating fat metabolism.

**Correct Answer: C. 0.7**