Glutamine is the most abundant amino acid (building blocks of proteins), representing 60%, and is one of the 11 non-essential amino acids in the body. Although our body can synthesize non-essential amino acids, under certain circumstances, conditional essential amino acids must be consumed through diet.

Amino Acid-Glutamine

Glutamine is one of the conditionally essential amino acids. During times of extreme physical and mental stress (for example, injuries, infections, burns, trauma, or surgical procedures) the level of glutamine might be low; in these cases, it will be helpful to take a glutamine supplement.
Additionally, as we get older, our bodies take longer time to produce glutamine and sufficient amounts will not generate.

 

Reference:

http://umm.edu/health/medical/altmed/supplement/glutamine

http://www.webmd.com/vitamins-supplements/ingredientmono-878-glutamine.aspx?activeingredientid=878

http://www.aminoacid-studies.com/amino-acids/glutamine-and-glutamic-acid.html