glutamine for building muscle really is not effective. HOWEVER glutamine for preserving muscle and keeping you out of catabolism when on a diet is extremely helpful (speaking from experience)...
When I am on a extreme diet (contest prep)... I will mix 10g glutamine/10g bcaa with some sugar free punch and sip on that my entire workout. When your calories are very low like on a diet, your body will want to canabolize its muscle stores (catabolism) along with your fat stores..this is where the glutamine and Bcaa can help out and shift that more towards fat then muscle...there will always be muscle wasting, the key is to minimize it.
*this is why you get weaker when your on a diet... for the trained athlete.