system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5 why does fiber cause gas?
gpt
Fiber refers to carbohydrates, such as cellulose, that aren't digestible by humans, and pass through the digestive tract relatively unaffected, at least on a molecular level.  This contributes to fullness / satiety, and it helps make sure that there's solid matter moving through the GI tract, which helps keep you regular. However, many types of bacteria in the intestines do have the ability to break down these carbohydrates.  The end products of these processes are generally simple compounds such as water, methane gas, and carbon dioxide.  And all that gas building up in the intestines builds up until the body has a release.