What is gas?

Intestinal gas (flatus) comes from two main sources: 90% from swallowing air and 10% from fermentation of foods by intestinal bacteria. Most healthy people pass between one and three pints of gas per day, and experience episodes of flatus about 15 times every day!

The composition of flatus is mostly odorless gases: nitrogen, carbon dioxide, hydrogen, methane, and oxygen.

Everyone swallows some air every day, in the course of talking or eating, or sometimes just as a nervous habit. Most people are unaware that they are doing this, so they cannot stop themselves from swallowing air.

Most of this swallowed air is burped or belched up, but some finds its way into the intestine. The 10% of intestinal gas produced in the large intestine (colon) by fermentation of
carbohydrates is mostly due to incomplete digestion of starches and certain sugars, which are contained in many foods including milk, beans, dark beer, red wine, onions, and certain fruits.