American Board of Surgery Qualifying Exam (ABS QE) Practice Test

What does an RQ of 1.0 indicate?

1. Pure fat utilization

2. Pure protein utilization

3. Pure carbohydrate utilization

4. Mixed nutrient utilization

The correct answer is: Pure carbohydrate utilization

An RQ, or respiratory quotient, is a measure used to assess the type of substrate being utilized for energy production in the body. An RQ value of 1.0 indicates that carbohydrate metabolism is predominant. This is because the complete oxidation of glucose (a carbohydrate) produces an equal amount of carbon dioxide and oxygen consumed, leading to an RQ of 1.0. In contrast, other substrates yield different RQ values: pure fat utilization results in an RQ closer to 0.7, while pure protein utilization has an RQ around 0.8. A mixed nutrient utilization scenario would yield an RQ value somewhere between these numbers, reflecting a mixture of carbs, fats, and proteins being metabolized. The presence of an RQ of 1.0 signifies effective carbohydrate metabolism, often seen in states where glucose is readily available and utilized, such as in a fed state after a carbohydrate-rich meal or during intense exercise when quick energy from glucose is needed.