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What I Need to Know About Gas

July 31, 2013

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Table of Contents

The digestive tract

The digestive tract

What Is Gas?

Gas is air in the digestive tract. Gas leaves the body when people burp through the mouth or pass gas through the anus* -- the opening at the end of the digestive tract where stool leaves the body.

Everyone has gas. Burping and passing gas are normal. Many people believe that they burp or pass gas too often and that they have too much gas. Having too much gas is rare.

What Causes Gas?

Gas in the digestive tract is usually caused by swallowing air and the breakdown of certain foods in the large intestine.

*See the Pronunciation Guide for tips on how to say the underlined words.

You typically swallow a small amount of air when you eat and drink. You swallow more air when you

  • eat or drink too fast
  • smoke
  • chew gum
  • suck on hard candy
  • drink carbonated or "fizzy" drinks
  • wear loose-fitting dentures
What Causes Gas?

Some of the air you swallow leaves the stomach through the mouth when you burp. Some swallowed air is absorbed in the small intestine. Some air moves through the small intestine to the large intestine and is passed through the anus.

The stomach and small intestine do not fully digest all of the food you eat. Undigested carbohydrates -- sugars, starches, and fiber found in many foods -- pass through to the large intestine. Bacteria in the large intestine break down undigested carbohydrates and release gas. This gas is passed through the anus.

Normally, few bacteria live in the small intestine. Small intestinal bacterial overgrowth (SIBO) is an increase in the number of bacteria or a change in the type of bacteria in the small intestine. These bacteria can produce excess gas and may also cause diarrhea and weight loss. SIBO is usually related to diseases or disorders that damage the digestive system or affect how it works, such as Crohn's disease or diabetes.

Which Foods Cause Gas?

Which Foods Cause Gas?

Most foods that contain carbohydrates can cause gas. Foods that cause gas for one person may not cause gas for someone else. Some foods that contain carbohydrates and may cause gas are

  • beans
  • vegetables such as broccoli, cauliflower, cabbage, brussels sprouts, onions, mushrooms, artichokes, and asparagus
  • fruits such as pears, apples, and peaches
  • whole grains such as whole wheat and bran
  • sodas; fruit drinks, especially apple juice and pear juice; and other drinks that contain high fructose corn syrup, a sweetener made from corn
  • milk and milk products such as cheese, ice cream, and yogurt
  • packaged foods -- such as bread, cereal, and salad dressing -- that contain small amounts of lactose, the sugar found in milk and foods made with milk
  • sugar-free candies and gums that contain sugar alcohols such as sorbitol, mannitol, and xylitol
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