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Flatulence (Gas) (cont.)

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.

Other causes of intestinal gas

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 develop.
  • Alterations in bowel habits can be a result of the following:
Medically Reviewed by a Doctor on 8/11/2015

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Read What Your Physician is Reading on Medscape

Malabsorption »

Malabsorption is a clinical term that encompasses defects occurring during the digestion and absorption of food nutrients by and infections of the gastrointestinal tract.

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