I would be careful before jumping to conclusions and assuming - saying it's the "protein", or the "glutamine" in you shake that is making you tired... Could also be any one of these OTHER ingredients: Proprietary non-GMO protein blend (rice protein, pea protein, and soy [isolated soy protein and fermented soy]), Fructose, Di-Calcium Phosphate, Xanthan Gum, Vanilla Flavor, FOS (Fructooligosaccharides), Guar Gum, Psyllium, Maltodextrin, Potassium Citrate, Magnesium Oxide, Oat Bran, Microcrystalline Cellulose, Spirulina, Vitamin C, Vitamin E, Choline Birartrate, Inositol, apple pectin, Bee Pollen, Niacinamide, Vitamin A Palmitate, Zinc Oxide, Manganese Sulfate, Ferrous Fumarate, Calcium Pantothenate, Lecithin, Lemon Bioflavonoids, Papaya, Bromelain, Chlorophyll, Pyridoxine HCI, Riboflavin, Thiamin (Vitamin B-1) (as Thiamine HCl), Vitamin B-12, Ergocalciferol, Folic Acid, Biotin, Potassium Iodide, Chromium Chloride, Sodium Selenate, Sodium Molybdate http://www.gnc.com/product/index.jsp?productId=2133797 Right of the bat I see one of the first ingredients and therefore a higher amount is "Vanilla Flavor" which is a dead give away for MSGlutamate. Almost ALL flavors including natural, are hidden forms of glutamates. They make me tired as hell. Get a protein powder with NO additives and see if it makes a difference. I know for me it does.