Most of the foul smell is Hydrogen Sulfide and a few other sulfer containing compounds.Protein is a main source of sulfer in the diet and many people get much more protein every day than they really need. For the most part anything you do not absorb becomes food for the bacteria in your colon. Some of them turn amino acids into Hydrogen Sulfide gas.Onions, Garlic, Eggs can also be sources of odor in the gas.Pepto Bismol is actually fairly effective at absorbing Hydrogen Sulfide so taking that can reduce the odor level.K.