## **Core Concept**
The protein efficiency ratio (PER) is a method used in nutrition science to evaluate the quality of a protein source. It is defined as the ratio of weight gain of the test subject (usually an animal) to the intake of a particular protein source. This measure essentially reflects how efficiently a protein supports growth.

## **Why the Correct Answer is Right**
The correct formula for the protein efficiency ratio is **(Weight gain of test group - Weight gain of control group) / Protein consumed**. This calculation directly assesses the efficacy of a protein source in promoting growth, compared to a control group that may not receive the protein or receives a standard protein source. The PER is particularly useful in comparing the nutritional value of different proteins.

## **Why Each Wrong Option is Incorrect**
- **Option A:** This option does not accurately represent the formula for PER. It seems to confuse the concept with another nutritional measure.
- **Option B:** Similarly, this option does not correctly represent the PER formula. It might be mixing elements of different nutritional assessment techniques.
- **Option D:** This option also does not accurately reflect the PER calculation. It seems to misinterpret the components involved in determining protein efficiency.

## **Clinical Pearl / High-Yield Fact**
A key point to remember is that the protein efficiency ratio is specifically used to assess the quality of dietary proteins. High PER values indicate high-quality proteins that are efficiently used by the body for growth and repair. This concept is crucial in nutritional science and dietetics, especially when planning diets for specific populations, such as children, athletes, or individuals with certain medical conditions.

## **Correct Answer:** B. Weight gain of test group - Weight gain of control group / Protein consumed.