I dunno about the stomach ache, but it's giving me a horrible case of
deja vu.
Seriously, though... what are the "benefits" that you're looking for? If another type of bread, even - shudder - white bread makes the ache go away, how's that bad? Maybe try some other brands and types and see if you find something that doesn't cause the problem. Food sensitivities tend to vary by individual and there's no quick and easy answer.