Oh really? Not to sound rude, but according to...?
Here's an explanation. I didn't write this.
With the exception of supplemental glutamine's beneficial role in gastrointestinal disorders (and general gut health), sepsis, and for the recovery from trauma and or surgery.... there's not much sense in administering a product that is very much limited in it's availability for physiological uptake, due to the fact that it's endogenous levels (prior to supplementation) are double the concentration of any other amino acid within the human body (1). Besides.... it's already synthesised within the body in large amounts, found in food, and found in significant amounts within a protein shake.
Endogenous glutamine plays a detrimental role in physiological homeostasis. It plays an equally important role in immune system functions, and most of the glutamine that is utilized for this purpose is naturally synthesized in vivo, and is supplied by the plasma glutamine. In healthy adults, the standard reference ranges for plasma glutamine are around 500-1000 mol/L (2), and do not require supplementation to maintain those figures.
Supplemental glutamine would only benefit us if our intracellular muscle glutamine concentrations were depleted. There are numerous studies that indicate no intracellular muscle glutamine depletion whatsoever following extensive exercise, but even if we do experience some glutamine attenuation.... we are still producing it within us, and getting it through our diet.
In healthy adults, dietary consumption of glutamine has been estimated to be around 5 grams per day (3). Foods such as meat, fish, dairy products, eggs, beans, cabbage, spinach, parsley, beets, ect. are all common sources. A single 3-oz serving of meat contains around 3-4 grams of glutamine. (4)
Now let's add on top of all that, the fact that an average 50 gram protein shake, there's about 4.5+ grams of glutamine. So for a 150 lb individual at only 2 protein shakes a day, that's around 9-10 grams of supplemental glutamine.
So for those of you that feel that glutamine is worth supplementing, we're looking at a minimum of around 15+ grams of glutamine intake per day, in addition to what is being produced endogenously.... Do you really think we need more?
(1)
http://jap.physiology.org/cgi/content/full/93/3/813
(2)
http://jn.nutrition.org/cgi/reprint/132/9/2580.pdf
(3)
http://gut.bmj.com/cgi/content/full/45/1/6
(4)
http://www.answers.com/topic/glutamine