Glutamine as a supplement is totally worthless.
Let's look at where most of the glutamine sales pitches start out:
"glutamine is the most abundant free amino acid…it makes up 2/3 of the muscle's free amino acid pool"
Sounds cool, right? But wait, what is 'free amino acid pool'?
Answer: It's a negligible portion of a muscle's total amino acid content. It just sounds cool.
What about the first part?
Answer: Glutamine is so abundant that you already get enough, unless you're a vegetarian or have some serious health problem. If you eat a high protein diet, then you already get more than you need.
Wait, but doesn't glutamine prevent muscle catabolism if i take it at certain times?
Answer: Maybe, but if it does it is so slight that it still hasn't been proven. Even if it does, you could get the effect to a much greater extent simply by drinking a glass of milk. (Or anything else with a good combination protein and fat.)