Intense exercise reduces levels of glutamine and glutathione, two substances needed for proper immune function. This immune depression correlates directly with the intensity and duration of the physical activity and the baseline immune status of the athlete. Scientists have theorized that an athlete's glutamine levels and immune status (as measured by the incidence of illnesses such as colds) are markers for overtraining syndrome (OTS).

The review listed below explains many of the benefits of supplementing with whey protein (WP).  Studies have shown that WP can dramatically improve cellular immune responses. When compared to animals fed standard lab chow or other proteins, those fed WP show enhanced immune responses to a variety of immune challenges. Scientists have yet to pin down the exact mechanism, but so far, it appears that WP modulates immunity via glutathione. WP is rich in glutathione precursors and rare glutamylcysteine groups (substances that support immune function) and raises glutathione levels in animals and humans.
 

Glutamine is also considered a conditionally essential amino acid, that plays a vital role with the immune system.  Glutamine levels within the muscles decrease as a response to stress.  This exercise can come from daily life or exercise.  It is important to replenish these glutamine levels through the diet by consuming a balanced diet that is rich in protein and vegetables. 

We suggest that all athletes supplement with whey protein as well as glutamine to help aid in the recovery process, to fight off colds and illnesses, and ultimately improve performance.