Gas (Flatus)

Topic Overview

What is gas?

Gas (flatus) is made in the stomach and intestines as your body breaks down food into energy. All people pass gas, some people more than others. It is normal to pass gas from 6 to 20 times per day.

Intestinal gas is made up of oxygen, nitrogen, hydrogen, carbon dioxide, hydrogen sulfide, ammonia, and methane. The foul smell usually is caused by small traces of gases such as hydrogen sulfide, ammonia, and methane. Gas that forms after eating meat and eggs tends to smell bad, while gas derived from fruits and vegetables usually does not have an odor.

What causes gas?

Common causes of gas include:

  • Swallowed air. If swallowed air is not burped up, it passes through the digestive tract and is released through the anus as flatus. Excessive air swallowing may cause hiccups.
  • Foods and beverages. The amount of gas that different foods cause varies from person to person.
  • Constipation. This can cause bloating but generally does not increase gas.
  • Medicines or nutritional supplements. Both prescription and nonprescription medicines, as well as dietary supplements, can cause bloating and gas as side effects.
  • A medical condition, such as a bowel obstruction or Crohn's disease.
  • Changes in hormone levels. It is common for women to have bloating right before their periods because their bodies retain fluid.

Can I treat or prevent gas?

You may be able to prevent gas by changing your eating and drinking habits. Occasionally gas is a symptom of a medical condition that requires treatment.

Examples of gas-producing foods are:

  • Vegetables such as artichokes, asparagus, broccoli, brussels sprouts, cabbage, cauliflower, cucumbers, green peppers, onions, peas, radishes, and raw potatoes.
  • Beans and other legumes.
  • Fruits such as apricots, bananas, melons, peaches, pears, prunes, and raw apples.
  • Wheat and wheat bran.
  • Eggs.
  • Carbonated drinks, fruit drinks, beer, and red wine.
  • Fried and fatty foods.
  • Sugar and sugar substitutes.
  • Milk and other dairy products, especially in people who have trouble digesting lactose, the main sugar found in milk.
  • Packaged foods that contain lactose, such as breads, cereal, and salad dressing.

Dietary supplements such as Beano may help to prevent gas.

Some people get relief from gas from products containing simethicone, a medicine that dissolves gas bubbles. Nonprescription medicines with simethicone include Gas-X and Mylicon.

Related Information

Credits

Author Jan Nissl, RN, BS
Editor Susan Van Houten, RN, BSN, MBA
Associate Editor Tracy Landauer
Primary Medical Reviewer H. Michael O'Connor, MD - Emergency Medicine
Specialist Medical Reviewer Adam Husney, MD - Family Medicine
Last Updated September 1, 2009

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