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Medical Author:

Joseph Maslar, MD

Coauthor:

Lance W Kreplick, MD, MMM

Medical Editor:

John P. Cunha, DO, FACOEP

John P. Cunha, DO, FACOEP

John P. Cunha, DO, is a U.S. board-certified Emergency Medicine Physician. Dr. Cunha's educational background includes a BS in Biology from Rutgers, the State University of New Jersey, and a DO from the Kansas City University of Medicine and Biosciences in Kansas City, MO. He completed residency training in Emergency Medicine at Newark Beth Israel Medical Center in Newark, New Jersey.

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Excess gas in the digestive tract (esophagus, stomach, small intestine, and colon/large intestine) can come from two sources: 1) increased intake of gas, for example, from air swallowed; or 2) increased production of gas as certain undigested foods are broken down by harmless bacteria normally found in the colon.

Swallowed air (aerophagia): This can occur with improper swallowing while eating or even unconscious swallowing of air out of habit.

• Activities that cause a person to swallow air include rapid drinking, chewing gum, use of tobacco products, sucking on hard candy, drinking carbonated beverages, loose dentures, and hyperventilation.
• Most people burp or belch to expel this excess swallowed air. The remaining gas moves into the small intestine. The air moves along to the large intestine for release through the rectum.
• Analysis of the gas can help determine if it originated from aerophagia (mostly nitrogen, also oxygen, and carbon dioxide) or GI production (mainly carbon monoxide, hydrogen, and methane).

Breakdown of undigested foods: If the body does not digest and absorb some carbohydrates (for example, the sugar, starches, and fiber found in many foods) in the small intestine because of a shortage or absence of certain enzymes there, this undigested food then passes from the small intestine into the large intestine, where normal, harmless bacteria break down the food, producing hydrogen, carbon dioxide, and, in about a third of all people, methane. Eventually these gases exit through the rectum.

• Foods that produce gas in one person may not cause gas in another. Some common bacteria in the large intestine can destroy the hydrogen that other bacteria produce. The balance of the two types of bacteria may explain why some people have more gas than others.
• Most foods that contain carbohydrates can cause gas. By contrast, fats and proteins cause little gas. These common foods and their natural components may create gas:
  • Beans: Beans contain large amounts of the complex sugar known as raffinose. Smaller amounts are found in cabbage, Brussels sprouts, broccoli, asparagus, and in other vegetables and whole grains.
  • Starches: Most starches (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.
  • Onions: The sugar known as fructose occurs naturally in onions, artichokes, pears, and wheat. It is also used as a sweetener in some soft drinks and fruit drinks.
  • Dark beer and red wine
  • Sorbitol: This sugar is found naturally in fruits including apples, pears, peaches, and prunes. It's also used as an artificial sweetener in sugar-free gum, candy, and other diet products.
  • Fiber: 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, 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 and some vegetables contain this kind of fiber.

Lactase deficiency: Another major source of flatulence is lactase deficiency, which results in a decreased ability to digest lactose, a natural sugar found in milk and other dairy products such as cheese and ice cream and in certain processed food such as bread, cereal, and salad dressing. This flatulence is often associated with diarrhea and cramping but can appear as only gas. Many people  normally have low levels of the enzyme lactase needed to digest lactose after childhood. 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.

Other problems: Certain conditions can result in other foods being poorly absorbed in the GI tract, allowing for increased bacterial activity.

• Malabsorption syndromes can be the result of decreased production of enzymes by the pancreas or problems with the gallbladder or lining of the intestines.
• If transit through the colon is slowed down for any reason, bacteria have increased opportunity to ferment remaining material. If a person is constipated or has decreased bowel function for any reason, flatulence can follow.
• Alterations in bowel habits can be a result of the following:
  • Poor dietary fiber
  • Parasites
  • Inflammatory bowel disease
  • Intestinal obstruction (including cancer)
  • Diverticulosis or diverticulitis
  • Poor thyroid function
  • Narcotic and other drug use

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