Which of the following is an essential amino acid?

Valine is classified as an essential amino acid because it cannot be synthesized by the body and must be obtained through diet. Essential amino acids play crucial roles in various physiological processes, including protein synthesis, tissue repair, and muscle metabolism. Since the body relies on external sources for essential amino acids like valine, consuming a balanced diet that includes protein sources such as meat, dairy, eggs, and certain plant-based proteins is important for maintaining overall health.

In contrast, alanine and glycine are non-essential amino acids, meaning the body can produce them on its own under normal conditions, reducing the necessity of obtaining them solely from dietary sources. This distinction highlights the importance of essential amino acids in nutrition and wellness.