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For further information, see CMDT Part 15-05: Gastrointestinal Gas

Key Features

  • The rate and volume of expulsion of flatus is highly variable

  • Healthy adults pass flatus up to 20 times daily and excrete up to 750 mL

  • Flatus is derived from two sources

    • Swallowed air (primarily nitrogen)

    • Bacterial fermentation of undigested carbohydrate

  • A number of short-chain carbohydrates ("FODMAPS") are incompletely absorbed in the small intestine and pass into the colon

    • Lactose (dairy products)

    • Fructose (fruits, corn syrups, and some sweeteners)

    • Polyols (stone-fruits, mushrooms, and some sweeteners)

    • Oligosaccharides (legumes, lentils, cruciferous vegetables, garlic, onion, pasta, and whole grains)

  • Abnormal gas production may be caused by increased ingestion of these carbohydrates or, less commonly, by malabsorption disorders

Clinical Findings

  • Chronic abdominal distention or bloating

  • Many patients have an underlying functional gastrointestinal disorder such as irritable bowel syndrome or functional dyspepsia

  • Constipation should be treated, and exercise (which accelerates gas propulsion) is recommended

  • Organic causes of acute bloating with distention, vomiting, and pain include

    • Ascites

    • Gastrointestinal obstruction (gastric fundoplication, gastric outlet obstruction, small intestine or colon obstruction, and constipation)


  • Determining abnormal from normal amounts of flatus is difficult

  • Lactose intolerance may be assessed by a 2-week trial of a lactose-free diet or by a hydrogen breath test


  • Conservative management for patients with a longstanding history of flatulence and no other symptoms or signs of malabsorption

  • The nonprescription agent Beano (α-d-galactosidase enzyme) reduces gas caused by foods containing galacto-oligosaccharides (legumes, chickpeas, lentils) but not other FODMAPS

  • Activated charcoal may afford relief

  • Simethicone is of no benefit

  • Probiotics may reduce flatus (anecdotal evidence)

  • Medications that inhibit gastrointestinal motility should be avoided (opioids and calcium channel blockers)

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