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What Causes Intestinal Gas?


Updated July 03, 2014

Woman drinking glass of milk, side view
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Question: What Causes Intestinal Gas?


You might find it reassuring to know that there are only two predominant causes of intestinal gas -- swallowed air and the bacterial breakdown of some substances found in certain kinds of foods. Having an awareness of these factors can help you avoid unwanted gas, bloating and flatulence.

Swallowed Air

In the normal course of the day, we all swallow some air. This air is generally released through the process of burping or belching. Air can also make its way to the large intestine where it is released through the rectum as flatulence. Certain factors can result in a larger amount of swallowed air:

  • Eating or drinking too quickly
  • Gum chewing
  • Smoking: cigarettes, cigars and pipes
  • Poorly fitted dentures

Bacterial Breakdown

Some substances in food are not well digested and absorbed by our bodies. When these substances, mainly sugars and soluble fiber, arrive in our large intestines, they are broken down by bacteria. The result of this breakdown is the release of gas. This gas is usually hydrogen, carbon dioxide, and in some cases, methane.

The primary food substances involved in intestinal gas are:


  • Soluble fiber: This type of fiber is commonly found in legumes like beans and lentils, and certain fruits and vegetables.

  • Raffinose: The high amount of this sugar in beans contributes to their well-earned gassy reputation. Raffinose is also found in vegetables such as cabbage and Brussel sprouts.

  • Lactose: This sugar is found in milk and other dairy products.

  • Fructose: This sugar is found in some fruits and vegetables as well as being a common ingredient in soft drinks.

  • Sorbitol: Sorbitol is naturally found in many fruits and is an artificial ingredient in many sugar-free food items.

Essential Reading from Dr. Bolen, Your IBS Guide:


National Digestive Diseases Information Clearinghouse (NDDIC) Gas in the Digestive Tract.

DISCLAIMER: The information contained on this site is for educational purposes only and should not be used as a substitute for diagnosis or treatment rendered by a licensed physician. It is essential that you discuss with your doctor any symptoms or medical problems that you may be experiencing.


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