Glutamine plays key roles in protein metabolism, cell volumizing, and anti-catabolism. Glutamine also increases your ability to secrete Human Growth Hormone, which helps metabolize body fat and support new muscle growth. Glutamine's anti-catabolism ability prevents the breakdown of your muscles.
This is especially useful for people 'cutting down'. Especially during summer when you're trying to get rid of some body fat without losing any muscle. Glutamine is needed throughout your body for optimal performance. Your small intestines requires the most Glutamine in your body, and your immune system also needs Glutamine because Glutamine levels deplete during workouts, bodybuilders are more susceptible to illnesses - this is why L-Glutamine supplementation is so important, not necessarily to gain more muscle, but for the 'maintenance' effects of L-Glutamine.
L-Glutamine supplementation promotes a positive nitrogen balance and prevents the loss of muscle. Recent studies have shown that taking just 2 grams of L-Glutamine can increase growth hormone levels by 400%.