Abdominal Distension or Gas in the Stomach (bloating)

Air swallowed with food or gases produced during the digestive process may cause abdominal distension or gas in the stomach. When this gas is brought out through the mouth, it is called belching. When it passes out via anus, it is known as flatus or more commonly, fart.

The main symptoms of gas are:

  • Distension of the abdomen
  • Eructation or belching
  • flatus or farting

Small amounts of air get swallowed with every mouthful of food, especially if a person is eating in a hurry. This causes distension of the stomach. When the stomach gets filled up with food, the air accumulated in there is usually brought up through the mouth. This is the usual reason for belching soon after a meal.

Some people may belch following a stressful situation. Hyperventilation during stress causes some air to be swallowed and this air gets expelled as belching. Tightness in the abdomen or chest, or discomfort, due to the accumulation of gas, is often relieved by belching.

Newborn babies and infants ingest large amounts of gas when they feed on milk, whether it is bottle feeding or breast feeding. Soon after feeding, they have to be winded by holding them in a position which makes it easy for the air to be expelled. Colic, which is very common in infants, is no longer considered to be due to gas accumulation in the stomach, as tests have not shown the presence of excess amounts of gas during episodes of colic. However, no alternative explanation is given for colic, either.

The gas expelled by flatus or farting is usually produced in the intestines during the digestive process. Almost all people have flatus, but the frequency as well as the amount of gas expelled during each flatus may vary from person to person. Typically, fifteen to twenty farts a day is normal. The gas expelled through the anus may be malodorous or not, depending on the composition of the gas.

The flatus usually contains hydrogen gas and methane, both of which are flammable but flatus is not known to pose any additional risk to fire safety even while working near or handling flames. But there were occasional reports of explosions caused, when electrical cauterization was done during colonoscopy, when the intestines have not been emptied properly prior to the procedure. The foul smell associated with flatus is due to the presence of methane gas and it is worsened when sulfur compounds are also present. Hydrogen and carbon dioxide are the odorless constituents of the flatus. The substances present in the food and the types of bacteria acting on them are responsible for the chemical composition of the flatus.


The causes of the different symptoms of gas are also different.

Belching is usually caused by external reasons such as:

  • Air swallowed along with food or while chewing gum
  • Carbonated drinks releasing the gas inside the stomach
  • Aerophagia or ingestion of large amounts of air

Air gets swallowed in small quantities whenever food or drink is swallowed. It accumulates in the stomach till it gets completely or almost completely filled with food. The air, being lighter, stays at the upper part of the stomach causing distension which is usually felt as a discomfort in the chest or upper part of the abdomen. When the air is expelled through the mouth by belching, it relieves the discomfort.

On reaching the stomach, the carbonated drinks release the carbon dioxide gas they contain, and it comes out forcefully through the mouth soon afterwards. Some people like this sensation, and others, who do not, can avoid taking carbonated beverages.

Swallowing large amounts of air is termed aerophagia and some people unconsciously do this especially in stressful situations. Hyperventilation or increased rate of breathing during stress is very common and some of the air inhaled gets swallowed and reaches the stomach. During smoking too, a lot of air is ingested when long draughts are taken. Excess salivation associated with nausea, gastropharyngeal reflux, wearing dentures especially if they are ill-fitting, or usage of certain drugs, also result in aerophagia due to the frequent swallowing of spit.

Some people develop a peculiar habit of taking in a bit of air only to bring it out as a belch in a futile attempt to bring up gas from their stomach, to get relief from an abdominal or chest discomfort. But since the ingested air only goes down into the esophagus before coming up again, it doesn’t help in relieving the discomfort.

Almost all of the air swallowed is expelled through belching, but a small quantity may reach the small intestine mixed with the food, and it gets absorbed into the blood and later passes out along with exhaled air. Swallowed air is not responsible for flatus.

Flatus is the result of internal processes associated with the digestion of food. The digestive system, especially the large intestine is host to a large number of microorganisms which help in the breakdown of many complex molecules in the food. Various gases such as carbon dioxide, methane and hydrogen are produced during this process and these byproducts are mopped up by some other bacteria. Some kind of balance often exists between these two processes. But sometimes more gas is formed, which upsets the delicate equilibrium, due to certain disorders or temporary situations such as:

  • Consumption of food items which are not easily digestible
  • Motility disorders which affect the muscles of the digestive tract
  • Change in the quantity and composition of intestinal flora
  • malabsortion or the inability of the intestines to absorb certain substances

Certain complex carbohydrates rich in dietary fiber such as those found in cabbage and beans are not easily digestible. While fiber adds bulk to the food and helps in relieving constipation; they also cause excess production of gas. Excess amounts of fat in the food, sugar alcohols like sorbitol used in special foods for dieters, as well as fructose sugar, cause gas formation. Flatulence is very common in people who consume plenty of fruits and vegetables.

Some people lack an enzyme called lactase which is essential for the breakdown of lactose sugar present in milk and other dairy products. When such people consume lactose rich foods, they cannot be digested and excess gas is produced. People with gluten sensitive enteropathy, celiac disease or wheat allergy also develop bloating when foods containing gluten are consumed. Consumption of substances a person is specifically allergic to, also results in bloating. Tropical sprue and pancreatic insufficiency are some of the malabsorption disorders which result in flatus.

The gas formation and resultant flatulence in some people may be due to motility disorder of the intestines. If the food passes through the stomach and intestines too fast, digestion of food and absorption of nutrients may not be complete. Undigested food in the large intestine leads to formation of gas.

Several types of bacteria inhabit the intestines, majority of them in the large intestine, and they operate in complex ways to further break down the undigested or partially digested substances. Different gases are produced during these processes and most of these gases are absorbed by other bacteria present. The action and composition of this intestinal flora keep changing, for example; during illnesses and antibiotic treatments. The type and amount of intestinal flora present in a person’s gut also may be responsible for variations in flatus.

Bloating is the condition characterized by the swelling or distension of abdomen, often accompanied by some amount of discomfort and less often pain. Bloating can result from gastroparesis due to abnormalities of the muscles and nerves of the intestines leading to incomplete emptying of the bowels, or from obstructive conditions like fecal impaction. People with cancer of the colon or ovary also may have distention of abdomen. A feeling of bloating and the need to belch may be felt by some people when they have a heart attack.

Bloating may result from excess gas accumulation in the stomach due to swallowing of excess air or from the consumption of aerated drinks. But a bloated feeling may be present even in the absence of gas accumulation. It is found that even small amounts of gas, usually considered normal, may give a feeling of bloating to some people, especially those with irritable bowel syndrome. People who have certain disorders such as bulimia or anorexia may have a faulty perception of bloating which may add to their stress. Hence, bloating may be real or perceived; and it may be due to gas or some other reason or maybe even unrelated to the digestive system; but due to its normal association with gas and acidity, over the counter antacids are liberally used when people have the feeling of bloating.


Symptoms such as bloating, belching and flatulence related to gas are very common, and often temporary, and may not require medical intervention. But when certain other symptoms appear along with symptoms of gas, it may be a cause for concern. The following warning signs may help people evaluate their condition and decide how urgently they need to seek medical attention.

Warning signs: When the following symptoms are present concurrently with the symptoms of gas, it may be an indication of some other underlying disorder.

  • Pain in the chest
  • Traces of blood present in stool
  • Recent loss of weight without any apparent reason

When to see a doctor:  When chest pain is present along with a sensation of bloating, it may indicate heart disease, and the patient should get immediate medical help, as it may be the only sign of a heart attack in some people. Those who have weight loss, or diarrhea with blood in the stool, also need to visit a doctor without delay. If the bloating causes too much discomfort, and frequent belching and flatus is disconcerting, people may consult a doctor.

When people approach a doctor with gas-related complaints, a physical examination is done to check distention of the abdomen and other signs which may indicate the presence of some stomach disorder. The medical history of the patient and detailed description of the symptoms, including the frequency, and any obvious association with foods taken, may help the doctor with diagnosis.

When the main complaint is frequent belching, doctor may look for reasons in the pattern of chewing and swallowing of food, which may cause excessive swallowing of air. Other habits such as gum chewing, smoking, frequent consumption of carbonated beverages are also taken note of. Doctor may check for possible reasons for hyper salivation.

If the patient has a complaint of frequent passing of gas, especially malodorous flatulence, doctor may ask details of dietary habits to find out the reason for the gas formation as well as to detect any possible food allergies. The color, texture and smell of feces are important details necessary for diagnosis of underlying disorders which may be causing the gas. Doctor may prescribe further testing, if malabsorption syndromes are suspected.

Recent changes in the diet such as inclusion of extra fiber, dairy or gluten rich foods (made of wheat, barley and rye), and any change in medications, including antibiotic therapy and regular intake of NSAIDs such as aspirin are taken into account. If warning signs such as weight loss and bloody diarrhea are present, rectal examination and pelvic examination for women may be conducted to detect the presence of obstructions or cancerous tumors

Testing: Tests may be necessary to determine the exact cause when doctor suspects disorders such as malabsorption, when the stool is loose or smelly or when fat globules are present. Blood tests for specific markers, indicative of lactase insufficiency and gluten intolerance, are done to detect such conditions. When recently developed symptoms of gas, especially distension of abdomen are present in older people, image testing and or colonoscopy is done to detect cancers of the colon or ovary.


When belching, bloating and flatulence are not associated with any other serious disorders, treatment is unnecessary and often ineffective. Doctors may help the patients understand that it is not abnormal or harmful to have belching after meals or flatulence fifteen to twenty times a day except for the risk to social acceptance.

If people could control the amount of air swallowed by altering their eating patterns, it may help reduce belching. But usually, the swallowing of air is an unconscious habit and people hardly notice it, and even when made aware, find it difficult to change. Avoiding hurried eating and slow chewing may reduce the amount of air swallowed. Gum chewing and consumption of aerated drinks as well as smoking are modifiable habits which may help in reducing belching. Developing a habit of breathing from the diaphragm has been found to be effective in reducing the swallowing of air.

If excessive flatulence is found to be associated with any specific food item, avoiding the same will help reduce the frequency. The offending food item can be identified by an elimination process starting from the usual known culprits such as cabbage, beans, fresh fruits, raw vegetables etc. some people find the inclusion of fiber rich bran or psyllium husk beneficial, while others find it worsening their symptoms.

Drug treatment: Anticholinergic drugs like simethicone or bethanechol may be prescribed, but their effectiveness is not proven. Malodorous flatulence can be modified by the use of tablets of activated charcoal, though it has the side effect of staining the mouth. Underwear lined with activated charcoal may help control the foul smell associated with some farts.

Use of probiotics, which contain beneficial bacteria and create an environment conducive to the proliferation of useful bacteria, may help reduce symptoms of gas such as bloating and flatulence. People who have disorders of the upper abdominal area such as dyspepsia or gastroesophageal reflux may get relief from bloating with the use of antacids. Those with frequent anxiety attacks may find the prescription of mild antidepressants helpful.

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Yasser Elnahas

MD, PHD, Professor Of CardioVascular Surgery
Dr. Yasser Elnahas, Is an associate Professor of Cardiovascular Surgery. Dr. Elnahas was trained as a fellow At Texas Heart Institute And Mayo Clinic Foundation.Dr. Elnahas is dedicated to educating the general public about different disease conditions and simplifying the medical knowledge in an easy to understand terminology.

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One Response to Abdominal Distension or Gas in the Stomach (bloating)

  1. Wm Chhum says:

    Pains that are due to bloating will feel sharp and cause the stomach to cramp. These pains may occur anywhere in the body and can change locations quickly.

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