Everybody produces gas, and everybody needs to pass gas. The amount depends on the individual, and there is a wide range of what is considered "normal". Passing gas is normal; nevertheless, it can be embarrassing or cause discomfort.
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.
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 travel 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.
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 that are 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.
Foods that May Cause Gas
Most foods that contain carbohydrates can cause gas. By contrast, fats and proteins cause little gas (although certain proteins may intensify the odor of gas).
The sugars that cause gas are raffinose, lactose, fructose and sorbitol. Raffinose - beans contain large amounts of this complex sugar. Smaller amounts are found in cabbage, brussels sprouts, broccoli, asparagus, other vegetables, and whole grains. Lactose is the natural sugar in milk. It is also found in milk products, such as cheese and ice cream, and processed foods, such as bread, cereal, and salad dressing. Many people, particularly those of African, Native American, or Asian background, have low levels of the enzyme lactase needed to digest lactose. Also, as people age their enzyme levels decrease. As a result, over time people may experience increasing amounts of gas after eating food containing lactose. Fructose – is naturally present in onions, artichokes, pears, and wheat. It is also used as a sweetener in some soft drinks and fruit drinks. Sorbitol is a sugar found naturally in fruits, including apples, pears, peaches, and prunes. It is also used as an artificial sweetener in many dietetic foods and sugar free candies and gums.
Most starches, including potatoes, corn, noodles and wheat, produce gas as they are broken down in the large intestine. Rice is the only starch that does not cause gas.
Many foods contain soluble and insoluble fiber. Soluble fiber dissolves easily in water and takes on a soft, gel-like texture in the intestines. Found in oat bran, beans, barley, nuts, seeds, lentils, peas, and most fruits, soluble fiber is not broken down until it reaches the large intestine where digestion causes gas. Insoluble fiber, on the other hand passes essentially unchanged through the intestines and produces little gas. Wheat bran, whole grains, and some vegetables contain this kind of fiber.
The most common ways to reduce the discomfort of gas are changing diet, taking medicines, and reducing the amount of air swallowed. Eating fewer fermentable vegetables/carbohydrates (like beans, broccoli, or cabbage), and avoiding sweeteners (like sorbitol and fructose) can lessen the amount of gas produced. Those who are truly lactose intolerant may improve if they avoid milk products.
Alcohol may impair intestinal digestion so that more food is available for gas production. Certain proteins may enhance the odor of gas. If gas is a problem for you, try monitoring your diet (time of day and description of foods eaten and drinks ingested, and times of each episode of gas) for a week or so to identify what may cause increased gas production or what may affect odor.
Doctors may tell people to eat fewer foods that cause gas. For some people this may mean cutting back on healthy food. Care should be taken not to eliminate food groups. Doctors may also suggest limiting high‐fat foods to reduce bloating and discomfort. This helps the stomach empty faster, allowing gases to move into the small intestine.
The amount of gas caused by certain foods varies from person to person. Effective dietary changes depend on learning through trial and error how much of the offending foods one can handle.
Many non-prescription (over-the-counter) medicines are available to help reduce symptoms, including antacids with simethicone and activated charcoal. Products containing chlorophyllin copper (e.g., Nullo, Derifil) can help minimize offending odor. Digestive enzymes, such as lactase supplements, actually help digest carbohydrates and may allow people to eat foods that normally cause gas.
Even though over‐the‐counter medicines are available without a prescription, it is a good idea to talk to your physician about the product usage and dosage most appropriate for you. Simethicone (e.g., Gas-X, Mylanta Gas, Phazyme) is a foaming agent that joins gas bubbles in the stomach so that gas is more easily belched away. However, these medicines have no effect on intestinal gas.
Activated charcoal tablets (e.g., Charco Caps, Charcoal Plus) may provide relief from gas in the colon. Studies have shown that when taken before and after a meal, intestinal gas is greatly reduced.
The enzyme lactase, which aids in lactose digestion, is available in liquid and tablet form without a prescription (e.g., Dairy Ease, Lactaid). Adding a few drops of liquid lactase to milk before drinking it or chewing lactase tablets just before eating helps digest foods that contain lactose. Also, lactose-‐ reduced milk and other products are available at many grocery stores.
Beano, an over‐the‐counter digestive aid, contains the sugar-digesting enzyme that the body lacks to digest the sugar in beans and many vegetables. The enzyme comes in liquid or tablet form. It is taken just before eating to break down the gas-producing sugars. Beano has no effect on gas cause by lactose or fiber. Heat degrades the enzyme in Beano so it cannot be added to food while it is being cooked. Beano is made from an enzyme (alpha-galactosidase) extracted from a food-grade mold; if you are allergic to molds you may react to Beano. Those with galactosemia (an inherited disorder characterized by the inability to metabolize galactose) should not use Beano without first consulting their physician.
Doctors may prescribe medicines to help reduce symptoms, especially for people with a motility disorder, such as irritable bowel syndrome. Promotility or prokinetic drugs, such as metoclopramide (Reglan) and cisapride (Propulsid), may move gas through the digestive tract quickly. For those who have chronic belching, doctors may suggest ways to reduce the amount of air swallowed.
Recommendations are to avoid chewing gum and to avoid eating hard candy. Eating at a slow pace and checking with a dentist to make sure dentures fit properly should also help.
Although gas may be uncomfortable and embarrassing, it is not life threatening. Understanding causes and ways to reduce symptoms, as well as seeking treatment advice will help most people find some relief.
Controlling gas – things to remember:
Everyone has gas in the digestive tract.
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 and 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 that may 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, and radishes Fruits, such as apples, peaches, and pears Whole grains and bran (Adding them slowly to your diet can help reduce the potential for gas) Fruit drinks and 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
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.
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 causes 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.
Adapted from National Digestive Diseases Information Clearinghouse
NIH Publication No. 97-883, May 1995 (Updated: November 1998) and the International Foundation for Functional Gastrointestinal Disorders ‐ Education Program Guide for Functional GI Disorders, 1997.