I went through about a dozen different proteins before I found one that does not cause me to have stomach issues. Biochem 100% Whey Protein. It’s 100% pure Ultra-Filtered/Micro Filtered Whey Protein Isolate. However, I do not like the taste.
Aspartame is another chemical sweetener that is in a lot of products and has quite a few bad reviews going for it. However, for whatever reason, this doesn’t seem to hurt my stomach. But I also only have aspartame if I have a stomach issue as I’ll drink Sprite Zero (seems to help).
Now, I didn’t have these issues when I first started working out. They were very minimal but it got worse over time. I have since cut out all lactose products and anything with sucralose and have not had any abdominal pain since. I am trying some egg proteins now that do not have lactose, sucralose, and taste good. However, with my current exercise program I am trying to get all protein from lean meats.
If you are having any bad GI abdominal pains Lactose Intolerance or Sucralose may be the culprit.
2015: I now take IDLife's Shake for lunch as a meal replacement (no stomach issues) and ID Nutrition. Very high quality and pharmaceutical grade ingredients. In addition, I also take About Time Protein to reach my 200g a day goal (muscles contain around 25% protein, so you need to get the proper amount to build muscle). Both are sweetened with Stevia, which doesn't cause me to have abdominal pains.
Or you can give Biochem 100% Whey Protein a try and see if that helps. You'll probably need to mix it with Rice Milk or add fruit to cover the taste. But consider the alternative, horrible abdominal pain.
Updated: Nov. 2015