Gas, also called flatus or flatulence, is air in the intestine that is passed through the rectum. Air that is passed from the digestive tract through the mouth is called belching.

Gas is formed in the intestines as food is being digested. Gas can make you feel bloated, which may cause crampy or colicky abdominal pain.

Gas can be caused by any of the following:

• Swallowing air while eating.
• Eating foods that are difficult to digest, such as fiber. If you recently introduced fiber into your diet, having gas may be temporary. Give it a little time. Your body may adjust and stop producing gas.
• Eating foods that you cannot tolerate -- for example, if you have lactose intolerance and eat dairy products.
• Irritable bowel syndrome -- a chronic form of stomach upset that gets worse from stress.
• Malabsorption (when your body cannot absorb or digest a particular nutrient properly, often accompanied by diarrhea).
• Antibiotics.

• Eat more slowly.
• Chew your food thoroughly.
• Avoid gum chewing.
• Relax while you eat.
• Avoid beans, cabbage, and carbonated beverages.
• Try Beano, a product sold over-the-counter at most drugstores, if you eat a lot of beans, fruits, vegetables, and other high-fiber foods.
• Walk for 10 to 15 minutes after eating.
• Drink peppermint or chamomile tea after a meal.

Call your doctor if:

• Your have other symptoms in addition to gas, like abdominal or rectal pain, heartburn, nausea, vomiting, diarrhea, constipation, or weight loss.
• You have oily, foul-smelling, or bloody stools.

Your doctor will perform a physical examination with special attention to your abdomen, and ask questions about your symptoms, such as:

• What is your diet like?
• Has it recently changed?
• What foods do you eat commonly?
• What foods have you eaten recently?
• Have you increased the fiber in your diet?
• How fast do you eat, chew, and swallow?
• Would you say that your gas is mild or severe?
• Does your gas seem to be related to eating milk products or other specific foods?
• What seems to make your gas better?
• What medications do you take?
• Do you have other symptoms like abdominal pain, diarrhea, early satiety (premature fullness after meals), bloating, or weight loss?

Diagnostic tests that may be performed include:

• Barium enema x-ray
• Barium swallow x-ray
• Blood studies such as CBC or blood differential
• Sigmoidoscopy
• Abdominal ultrasound  
• Abdominal CT scan
• Upper endoscopy (EGD)  

Birrer RB. Irritable bowel syndrome. Dis Mon. 2002; 48(2): 105-143.

Lovelace HY. Diagnosis, symptoms, and calcium intakes of individuals with self-reported lactose intolerance. J Am Coll Nutr. 2005; 24(1): 51-57.

Andrès E. Food-cobalamin malabsorption in the elderly. Am J Med. 2002; 113(4): 351-352.