Flatulence occurs when a food does not break down completely in the stomach and small intestine. As a result, the food makes it into the large intestine in an undigested state. For example, if you are "lactose intolerant," it means that you lack an enzyme (lactase) in your intestine—the enzyme that breaks lactose apart into two sugar molecules so they can enter the bloodstream. Certain foods produce more flatulence than others do because they contain more indigestible carbohydrates than others do.