I have the same problem with Mg: no matter how much I take, I never get loose BMs and I'd like that effect of Mg because I'm constipated. I'm taking now Mg Malate.
The bottle says: Mg (as Mg malate & AAC ?? ) - 300mg
Malic acid (Magnesium malate) 1.5g
Always wondered why for so many people Mg is a laxative and for a few it is not. There may be some co-factors in my body that contribute to proccesing Mg differently.
Would be good to know which ones.