I've been experimenting with Whey Protein as well. It tends to loosen my stools quite a bit, so instead of being C I get loose BM's, sometimes nearing full-blown D. I've learned I have to cut back to every other day or every second or third day. But, on the days I do drink it, I have a lot more energy and it's way easier to do some weight work. I'm trying to rebuild my muscles, too, but for me it's been many years (6) since I've had any decent muscle tone. I like it with a little bit of heavy cream and sometimes I can even tolerate a little tiny bit of instant coffee. I have a hard time drinking it straight as I hate vanilla flavored anything. As long as I stay away from carbs for 2 or 3 hours before and after the shake I don't have a problem. For some reason I do better not mixing carbs and proteins/fats.