When the body needs to clean out the digestive system in a hurry, it pours water into the digestive system. The watery material makes a run for the colon, and from there out of the body. And that, boys and girls, is how diarrhea is made. Having too much undigested sugar will cause diarrhea via osmosis. The flatulence is often the result of the stool making its way through your system and pushing everything in its path ahead of it.