I take magnesium glycinate, 2 every night with dinner, which is 200 mgs. I swear on my LIFE by them. They have helped me so much! Even when I mess up on my diet by not getting enough fiber, these things help me to stay soft. Now, thats not to say that you can just chuck your fiber diet out the window and just take these things. I'm sure we all would if we could get away with it but we all know better.
You are right about the diarrhea. Its basically the same things as taking MOM but in pill form, so you have to be careful. I started out with just 100 and went up in increments of 100 until I found the right amount. 200 mgs works for me but it may be different for you. Just make sure you drink enough water, otherwise these things won't do you as much good as they could.
I swear by them though and Magnesium Glycinate is supposed to be the form of magnesium that absorbs best.
So best of luck. If I were you I would split one of your pills in half and start with that.
Good luck!
Kate