Vitamin B will turn pee bright neon green with the right concentration, and I definitely notice a difference in aroma depending on what was consumed the evening before.
As for gas, oy. When I was totally new to brewing I made a batch of extract imperial stout, on bottling day my friend and I ran out of bottles. We had already consumed many bottle conditioned european beers, mostly from around the Baltic sea, we then ate massive amounts of rice and beans, after that we finished off the unbottled and primed imperial stout. The next day was spent in complete agony with CO2 moving around inside of us in places we didn't know it could collect, we're pretty sure we diluted our gastric juices enough to allow the yeast to continue fermenting inside our guts for the next several hours...
It was excellent beer, though!