Flatus & Bloating

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)

Diagnosis

• 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

Treatment

• 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)