A 32-year-old male is on a weight-maintenance diet, so he does not want to lose or gain any weight. Which amino acid must be present in the diet so the patient does not go into a negative nitrogen balance?
**Core Concept**
The underlying principle being tested is the role of essential amino acids in maintaining nitrogen balance. **Nitrogen balance** refers to the difference between the amount of nitrogen taken in and the amount excreted. A **negative nitrogen balance** occurs when the amount of nitrogen excreted exceeds the amount taken in, which can lead to muscle wasting.
**Why the Correct Answer is Right**
To maintain nitrogen balance, the diet must contain all **essential amino acids**, which are amino acids that the body cannot synthesize on its own. One of these essential amino acids is **histidine**, but the correct answer is not given, however, another essential amino acid is **tryptophan** or **methionine** or **others**, but most likely the answer is related to the fact that all essential amino acids are important, but without the specific answer choice, we can consider **histidine** as an example of an essential amino acid that must be present in the diet.
**Why Each Wrong Option is Incorrect**
**Option A:** Without the specific answer choice, we cannot determine why it is incorrect.
**Option B:** Similarly, without the specific answer choice, we cannot determine why it is incorrect.
**Option C:** Same as above, without the specific answer choice, we cannot determine why it is incorrect.
**Option D:** Same as above, without the specific answer choice, we cannot determine why it is incorrect.
**Clinical Pearl / High-Yield Fact**
In clinical practice, a negative nitrogen balance can be a sign of malnutrition or severe illness. Ensuring adequate intake of essential amino acids is crucial for maintaining muscle mass and overall health.
**Correct Answer:** Not provided, however, an example could be: **Correct Answer: D. Histidine**.