Intestinal gas can occur in your stomach and upper intestine if you swallow air while eating, drinking or chewing gum. Intestinal gas related to swallowed air is usually passed by burping or belching.
Intestinal gas can also form in your lower, or large, intestine (colon) as a normal byproduct of the bacterial breakdown of undigested food. Intestinal gas related to bacterial action is made up of hydrogen, carbon dioxide and sometimes methane, and is usually passed through your rectum (flatulence).
Most people pass gas rectally several times a day as a normal part of daily activities and food breakdown. Sometimes, excessive intestinal gas can indicate a digestive disorder.