There is a blog I followed for a while and then lost track of that had a post with pictures of the author's daughter's tummy after eating something with wheat flour and how bloated she was, and then an After picture after they'd removed grains from the diet. I was hoping to find the photos but she's re-done her website and I can't locate them now, but the difference was pretty profound, especially considering it was a 4YO!
Whether or not it's an intolerance, all that starch breaking down provides lots of "food" for gut flora; in the case of any yeast that live there naturally, that'll result in CO2 production, just like yeast in bread dough makes bubbles. A steady food supply *can* result in yeast overgrowth in the body, so something to bear in mind even when picking substitutions for wheat flour, as pretty much any grains will break down the same way.