Can yeast ferment in your bowels?
1 Q how much sugar is there in bread ( this would be used to make the so called alcohol in it) I make my bread at home and it has no sugar at all, yeast is in bread to make it rise- thats it, and as far as a fermenting gut goes, could it be maybe that you were mixing beer with milk in your bowels that caused this effect, its not called fermenting its called Curdling
The laxative and flatulant effects of live yeast are well documented. And some of those billions of yoghurt bacteria do survive to your guts, just not very many 
Good old Palmer (again):
Good old Palmer (again):
I agree that it's probably possible to lower the stomach pH to levels where the yeast would survive, and I'd even be guessing that some yeast would survive even at pH 1 which is the normal stomach acid pH.One final item that nobody ever remembers to tell new brewers until it's too late is: "Don't drink the yeast layer on the bottom of the bottle." People will say, "My first homebrew was pretty good, but that last swallow was terrible!" or "His homebrew really gave me gas" or "It must have been spoiled, I had to go to the bathroom right away after I drank it." Welcome to the laxative effects of live yeast!
w00t!