Only 1 percent of what makes up a fart is responsible for that fart's odor. As much as 99 percent of a fart is carbon dioxide, hydrogen, nitrogen, oxygen and methane. The exact makeup of your farts is personal, like a fingerprint -- the biology of a gut differs from person to person. But it's actually the small remainder of intestinal gas -- sulfurous gases -- that can really stink up a room. Hydrogen sulfide, for example, gives farts a sulfury, rotten egg odor, while flatulence that smells like rotting cabbage is likely caused by a build-up of methanethiol. Sweet-smelling farts? That's dimethyl sulfide to blame. [source: Kluger]. Diet matters when it comes to how stinky our farts are, and it's not just sulfur-containing foods such as cabbage and kale (although they don't help) -- a diet full of complex carbohydrates (fiber, sugar and starches) is a diet full of flatus.