I swear by Carnivore line of protein. It's all beef, no whey, and I never feel any gut rot or upset stomachs. Flavor is great and mixes perfect. I usually get the MASS tub as it has BCAA's in it as well. If your experiencing gut rot I would highly suggest trying all beef and getting away from Whey.
http://ca.bodybuilding.com/store/mus...ivor-mass.html
I have a fruit and protein shake right when I wake up, then food for the rest of the day and a shake right after working out before my next meal.
Berz out.