This can be a cause of excessive flatulence. If lactase deficiency is suspected of causing your gas, your doctor may tell you to stop eating dairy products for a while to see if you will have less gas. The doctor also may give you a blood test or a breath test to find out if you are lactose intolerant. The breath test detects hydrogen that is released by the bacteria as the undigested lactose ferments in the colon. The amount of gas that people produce varies.
Most people produce between a pint and a half gallon of gas each day.
Oxygen, carbon dioxide, and nitrogen from swallowed air make up a large part of flatus. Fermenting foods in the colon produce hydrogen and methane as well as carbon dioxide and oxygen. The unpleasant odor of some flatus is the result of trace gases, such as hydrogen sulfide, indole, and skatole, which are produced when foods decompose in the colon. Eating a lot of fatty foods can cause bloating and discomfort because the fat delays stomach emptying, allowing gas to build up. This problem can be avoided by eating less fatty meals.