ISSA Nutritionist Practice Exam

Which branched chain amino acid is most used by the body?

1. Leucine

2. Valine

3. Isoleucine

4. Serine

The correct answer is: Leucine

Leucine is identified as the most used branched-chain amino acid (BCAA) by the body, and this is largely due to its unique role in protein synthesis and muscle recovery. It plays a critical part in stimulating the mTOR pathway, which is essential for muscle growth. As a result, leucine facilitates an anabolic environment in the body, making it particularly important for those engaged in resistance training and intense physical activity. While valine and isoleucine also serve important functions—such as energy production and muscle metabolism—they do not have the same level of influence on muscle protein synthesis as leucine does. Serine, although biologically significant, is not classified as a branched-chain amino acid and is involved in different metabolic pathways primarily related to the synthesis of neurotransmitters and other important biomolecules. Therefore, leucine's prominence in muscle-building processes solidifies its status as the most utilized branched-chain amino acid in the body.