What is one of the primary functions of glutamine in the body?

Glutamine plays a crucial role in several metabolic processes within the body, and one of its primary functions is indeed related to enhancing protein and glycogen synthesis. It is categorized as a conditionally essential amino acid, particularly important during periods of stress or intense physical activity, when the body's demand for glutamine increases.

During exercise, glutamine levels can deplete, and replenishing it helps support muscle recovery and growth. Glutamine assists in nitrogen balance, which is pivotal for protein synthesis. Additionally, it serves as a substrate for gluconeogenesis—the process of synthesizing glucose from non-carbohydrate sources—thereby playing a notable role in maintaining energy levels and supporting glycogen stores in muscles, especially after exercise. This ability to influence both protein and glycogen metabolism underscores its importance in a sports nutrition context, where optimizing performance and recovery is critical.

The other options do not accurately capture glutamine's primary function. While it does contribute to energy metabolism, it is not the main energy substrate for neurons, nor does it function solely as a neurotransmitter or provide insulation for nerve cells. Thus, its role in enhancing protein and glycogen synthesis stands out as essential to understanding how glutamine functions within the body.