Everybody produces gas, and everybody needs to pass gas. The amount depends on the individual, and there is a wide range of “normal.” Passing gas is normal; nevertheless, it can be embarrassing or cause discomfort. A better understanding of what causes intestinal gas can help most people reduce symptoms and find some relief.
Sources of Intestinal Gas
Gas in the digestive tract (the esophagus, stomach, small intestine, and large intestine) comes from two sources:
- swallowed air and
- the normal breakdown of certain undigested foods by harmless bacteria that are naturally present in the large intestine.
Swallowed Air – Air swallowing (aerophagia) is a common cause of gas in the stomach. Everyone swallows small amounts of air when eating and drinking. However, eating or drinking rapidly, talking while eating, chewing gum, smoking, or wearing loose dentures can cause some people to take in more air.
Burping, or belching, is the way most swallowed air leaves the stomach. The remaining gas moves into the small intestine where it is partially absorbed. A small amount travels into the large intestine for release through the rectum. (The stomach also releases carbon dioxide when stomach acid and bicarbonate mix, but most of this gas is absorbed into the bloodstream and does not enter the large intestine.)
Bacteria – Gases are produced as a by-product when certain food materials are digested by naturally occurring bacteria in the large intestine, or colon. These bacteria are responsible for digesting materials like complex carbohydrates (sugar, starches, and fiber found in many foods) and cellulose, which are not normally digested in the upper gastrointestinal tract.
The quantity and mixture of gases depend on the types of bacteria in the colon; everyone has a unique assortment of bacteria from the time of birth. These gases include hydrogen, carbon dioxide, and, in some people methane. Trace gases, such as hydrogen sulfide, are responsible for the odor. Foods that produce gas in one person may not cause gas in another.
Tips on Controlling Intestinal Gas
Everyone has gas in the digestive tract, but people often believe normal passage of gas to be excessive. Gas comes from two main sources: swallowed air and normal breakdown of certain foods by harmless bacteria naturally present in the large intestine.
- Swallowed air can be affected by a number of contributing factors. Dentures that do not fit well can cause people to swallow more saliva which carries air bubbles; postnasal drip tends to make people swallow more often, carrying more air to the stomach; smoking a cigar or pipe may increase the amount of saliva produced and swallowed; eating too fast increases the amount of air swallowed; gum chewing and sucking on hard candies also increases the amount of air swallowed.
- Many foods with carbohydrates can cause gas. Fats and proteins cause little gas.
- Foods more likely to cause gas include:
- Beans (Presoaking reduces the gas-producing potential of beans if you discard the soaking water and cook using fresh water)
- Vegetables such as artichokes, asparagus, broccoli, cabbage, Brussels sprouts, cauliflower, cucumbers, green peppers, onions, radishes, celery, carrots
- Fruits such as apples, peaches, raisins, bananas, apricots, prune juice, pears
- Whole grains and bran (Adding them slowly to your diet can help reduce gas forming potential)
- Carbonated drinks (Allowing carbonated drinks, which contain a great deal of gas, to stand open for several hours allows the carbonation/gas to escape)
- Milk and milk products, such as cheese and ice cream
- Packaged foods prepared with lactose, such as bread, cereal, and salad dressing
- Foods containing sorbitol, such as dietetic foods and sugarfree candies and gums
- Beverages such as wine and dark beer
- Odor forming foods may include: alcohol, asparagus, beans, cabbage, chicken, coffee, cucumbers, dairy products, eggs, fish, garlic, nuts, onions, prunes, radishes, and highly seasoned foods.
- Foods less likely to cause gas include:
- Meat, poultry, fish
- Vegetables such as lettuce, tomatoes, zucchini, okra,
- Fruits such as cantaloupe, grapes, berries, cherries, avocado, olives
- Carbohydrates such as gluten-free bread, rice bread, rice
- The most common symptoms of gas are belching, flatulence, bloating, and abdominal pain. However, an intestinal disorder, such as irritable bowel syndrome, rather than too much gas often cause some of these symptoms.
- The most common ways to reduce the discomfort of gas are changing diet, taking nonprescription or prescription medicines, and reducing the amount of air swallowed.
- Digestive enzymes, such as lactase supplements, actually help digest carbohydrates and may allow people to eat foods that normally cause gas.
- How we respond to dietary components varies from person to person. For one week try eliminating foods or beverages in your diet that you suspect most likely are causing you gas or odor problems. Then gradually reintroduce them one at a time to help identify the offenders.
Adapted from IFFGD Publication #155 compiled by William F. Norton, Publications Editor, International Foundation for Functional Gastrointestinal Disorders, Milwaukee, WI.