Most protein powder's shouldn't upset your system, unless you know spicificly what sources of protein do infact upset your system. Whey protein is low in lactose and easily absorbed, but whey shouldn't be your only sorce of protein, even in powder form. I suggest you go to your nearest health food store and buy 1 pound or even 1/2 pound servings of these proteins and access your tolerance. Whey, Egg, and soy. If you don't notice any side effects from using these individually, feel free to combine any or all 3 in a shake. 1 tablespoon of any of these will yield roughly 11-12 grams of protein each, with hardly any carbs or fat to worry about.
Hope this helps
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