Gas in the digestive tract occurs in all people. This gas is composed mainly of oxygen, carbon dioxide, nitrogen, hydrogen and, occasionally, methane. It is released through the mouth by burping (belching) or through the rectum (flatulence).

Bloating refers to an unpleasant sensation of fullness or swelling in the abdomen. It may result from many causes, including an accumulation of gas in the stomach and intestines. Abdominal pain often accompanies bloating.

Most gas in the stomach is swallowed (usually during a meal). Much of this gas is eliminated by burping, and very little enters the large intestine. However, gas within the large intestine is created when harmless bacteria consume undigested foods. The action of these bacteria causes the unpleasant odor in gas.

Most people who believe they produce (and pass) too much gas actually produce the same amount as others. The average person produces between one and four pints (about 0.5 to 1.9 liters) of gas per day, and passes the gas 14 to 23 times a day.

Patients whose gas and bloating is accompanied by recurrent, severe or prolonged abdominal pain should seek medical attention because this may indicate the presence of another underlying condition (e.g., irritable bowel syndrome) – especially if they also experience bleeding, nausea, vomiting, fever or weight loss. The physician will perform a physical examination and compile a thorough medical history. Screening tests (e.g., endoscopy) may also be conducted to help determine the cause of gas and bloating.

Most gas symptoms that are unrelated to a medical condition are usually brief. Because of this, gas is often treated conservatively by minimizing further symptoms with lifestyle changes or over-the-counter gas-reducing products.

Problems caused by gas can often be relieved by identifying and eliminating the factors that cause the gas. When using medications, it is generally considered best to experiment with only one gas-reducing product at a time. Exercise (e.g., walking, jogging) helps to stimulate the passage of gas through the digestive tract, easing symptoms.

Gas occurs throughout the gastrointestinal tract. This includes the esophagus, stomach, small intestine and large intestine. Bloating is an unpleasant sensation of fullness or swelling in the abdomen that is sometimes (but not always) due to the buildup of gas in the abdomen.

Most gas results from swallowing air (aerophagia). It is normal to swallow a small amount of air when eating or drinking. However, when people eat or drink too quickly, they tend to swallow more air. Much of the air ends up in the stomach in the form of gas. A small amount may also enter the small intestine.

Gas also develops in the large intestine due to the presence of harmless bacteria. The bacteria consume undigested food (e.g., carbohydrates) and gas is the byproduct.

Although the exact composition of intestinal gas varies among people, more than 99 percent of intestinal gas is composed of nitrogen, oxygen, carbon dioxide, hydrogen and sometimes methane. These gases are odorless. The unpleasant odor associated with intestinal gas is due to the bacteria, which release sulfur. Foods rich in sulfur include cauliflower, eggs and meat. These foods often cause flatus with offensive odor.

Most people produce between one and four pints (about 0.5 to 1.9 liters) of gas per day. Some gas in the digestive tract is absorbed into the blood through the gastrointestinal (GI) lining and excreted by the lungs. The remaining gas is released in one of two ways:

• Burping (belching or eructation). The expulsion of gas in the stomach through the mouth. It may be voluntary or involuntary. Belching often occurs when the stomach is full. It is normal to occasionally belch during or after meals. Some individuals may experience a tight feeling in their chest or stomach just before belching. This tightness generally goes away after the belch.
  
  
• Flatus (flatulence). The expulsion of gas in the intestines through the anus. It may be voluntary or involuntary and quiet or noisy. The expulsion causes the anal sphincter (the circular muscle that closes the anus) to vibrate. The amount of gas, force of expulsion and resistance from the sphincter determine the volume and pitch of the flatus. Sometimes, an individual may also pass a small amount of stool when passing gas.

The average person passes gas 14 to 23 times per day. Many patients who report gas-related symptoms, such as bloating, do not actually produce more gas than others, but are instead more sensitive to the normal amount of gas in their bodies.

Bloating due to excessive gas is actually rare. A number of conditions can make a person more sensitive to gas in their bodies. Some are related to the GI system, such as irritable bowel syndrome (IBS), whereas others may be psychological in origin. For instance, people with eating disorders often report bloating.

Abdominal pain often accompanies bloating. This pain may be mild and dull or intense and sharp. It may feel constant or may come and go. Jabbing pain, cramps, and/or a knotted feeling in the stomach may occur. This pain can occur anywhere in the abdomen and can change location quickly.

Abdominal pain most often occurs when gas becomes trapped in the colon. Gas is most likely to get caught in areas where the colon bends sharply (e.g., the upper right and left parts of the abdomen). When it occurs in the upper left side, this pain may be mistaken for a heart problem. When it occurs in the right side, it may be mistaken for gallstones or appendicitis. However, in most cases, the pain subsides with the flatus or a bowel movement.

According to the American College of Gastroenterology (ACG), up to 7 percent of the general population complain of excessive or bothersome belching and about 11 percent report frequent bloating. However, some populations do frequently produce more gas than others. These individuals include:

• Smokers
  
  
• Vegetarians
  
  
• People who regularly drink carbonated beverages or beverages with high levels of sulfates (e.g., beer, wine)
  
  
• People who regularly chew gum
  
  
• People who regularly eat a lot of gas-producing foods, such as cabbage, brussel sprouts and other foods containing a carbohydrate called raffinose
  
  
• People with certain chronic intestinal conditions or food intolerances (e.g., irritable bowel syndrome)

Gas is a normal byproduct of digestion. It also occurs due to the swallowing of air (aerophagia). Symptoms of gas may be made more frequent or worsened by numerous factors, ranging from diet to everyday habits.

Swallowed air is a frequent cause of gas and comprises most of the gas in the stomach. It may also be passed into the intestines. Some air is swallowed whenever a person eats or drinks. Gulping food quickly will cause more air to be swallowed. Other ways air is swallowed include:

• Drinking from straws, small-mouthed bottles or water fountains
  
  
• Activities that stimulate the production of saliva (e.g., chewing gum, sucking on hard candies)
  
  
• Loose-fitting dentures
  
  
• Cigarette smoking

Many people swallow air when they are nervous (nervous aerophagia). Stress may also increase a person’s sensitivity to normal levels of gas. This combination often results in more frequent or worse symptoms following periods of stress or anxiety.

Some patients induce belching (burping) by swallowing air and releasing it rapidly. Many people may believe that this will relieve the discomfort of gas symptoms. However, it actually introduces more gas into the stomach and usually makes symptoms worse. This activity often develops into a habit. The patients may not realize what they are doing. Such habitual swallowing of air frequently results in episodes of repeated belching.

Gas is also produced in the intestines. The amount and composition of gas produced during digestion depends largely on a person's diet. However, foods that produce gas in one person may not do so in another. Foods that are not fully digested in the small intestine are passed into the colon. Here, normal intestinal bacteria break down the undigested food in a process called fermentation. Gas is released by the bacteria as a byproduct of fermentation. Foods containing Fiber and carbohydrates are frequently responsible for gas.

There are two different kinds of fiber. Soluble fiber dissolves in water. It is not broken down until it reaches the colon, where it produces gas. Many foods, including beans, oat bran, peas and most fruits contain soluble fiber. Insoluble fiber passes through the digestive tract nearly intact. It is not broken down, so it produces little gas. Wheat bran and some vegetables contain insoluble fiber. Fiber supplements may also cause gas.

Rice is the only starch (carbohydrate) that does not cause gas. It is broken down entirely in the small intestine. Other carbohydrates contain materials that may be difficult to digest, including:

• Raffinose. A common sugar in many vegetables. Beans contain large amounts of this sugar. It is found in smaller amounts in many other vegetables, including cabbage, brussel sprouts, broccoli and asparagus. It is also present in whole grains. Humans lack the enzyme necessary to properly digest raffinose.
  
  
• Lactose. A sugar present in milk and other dairy products (e.g., cheese, ice cream). It is also found in some processed breads, cereals and salad dressings. The ability to efficiently process lactose decreases with age in many individuals.  These people have less lactase (enzyme that breaks down the milk sugar lactose) production after adolescence. Some ethnic groups (Asians, African-Americans, Native Americans) tend to have less lactase production than the general population. Some people are lactose intolerant because of minimal or no lactase production. Breath-testing can formally diagnose lactase-deficiency.
  
  
• Fructose. A sugar found in onions, artichokes, wheat and most fruits. It is also used as an artificial sweetener in some soft drinks, fruit drinks and processed foods. Fructose may cause considerable gas in some people and little in others.
  
  
• Sorbitol. A sugar present in many fruits (e.g., apples, pears, peaches, prunes). It is also used as an artificial sweetener in some sugar-free foods, candies and chewing gums. These foods are often used for people with diabetes. Most people have little problem digesting sorbitol. However, it results in large amounts of gas in others.

Many foods cause gas or gas symptoms even though they are not difficult to digest. Carbonated beverages are responsible for some gas. These beverages contain carbon dioxide gas, which is released into the digestive tract. Fatty foods do not necessarily cause excessive gas, but they can delay stomach emptying. This often results in bloating and discomfort. Some foods (e.g., peppermint, chocolate, fats) relax the muscle between the esophagus and stomach (lower esophageal sphincter). This may result in increased belching, heartburn and acid reflux.

Many medications can interrupt the normal process of digestion. Antibiotics often disrupt the balance of normal intestinal flora. Some bacteria may be killed, allowing other bacteria to overgrow. The overgrown bacteria may produce more odorous or increased amounts of gas. Some medications may also inhibit digestive enzymes or contain indigestible sugars. Excessive use of laxatives or constipation drugs may also contribute to gas.

Gas is not usually a sign of a medical problem. However, in some cases it can signal the presence of an underlying  condition, the most common of which involve food intolerances. Food intolerances occur when the body is unable to properly digest a component of food. This component passes into the colon, where fermentation takes place and gas is created.

For instance, Celiac disease, or gluten intolerance, occurs in patients who have a small intestinal inflammatory reaction to gluten. The small intestinal inflammation causes malabsorption of nutrients leading to excessive gas. Gluten is a protein found in wheat and some other grains.

Other medical conditions that may cause or aggravate gas and bloating symptoms include:

• Constipation. Food particles that remain in the colon longer have more time to ferment. The longer they ferment, the more gas is produced.
  
  
• Premenstrual syndrome (PMS). Many women experiencing PMS also experience symptoms of gas.
  
  
• Gastroesophageal reflux disease (GERD). When acid refluxes into the esophagus, patients may swallow repeatedly to clear it. This results in swallowing more air.
  

  

• Irritable bowel syndrome. Characterized by increased bowel sensitivity. This includes increased sensitivity to normal amounts of gas.
  
  
• Bowel obstruction. Intestinal blockage may trap gas, often resulting in bloating and abdominal pain.
  
  
• Diabetes and scleroderma. Patients with these conditions may develop sluggish small intestinal movements (peristalsis). This may cause bacterial overgrowth in the bowel, resulting in poor digestion and excess gas.
  
  
• Inflammatory bowel disease. Diseases that cause inflammation of the intestines, including Crohn’s disease and ulcerative colitis. These conditions may increase bowel sensitivity and aggravate gas symptoms.
  
  
• Pancreatitic insufficiency. Patients with chronic pancreatitis, cystic fibrosis or other conditions associated with diminished pancreatic enzyme production may have excess bloating and flatulence due to diminished fat digestion. Pancreatic enzymes may be taken orally to help fat digestion and lessen symptoms.
  
  
• Diverticulitis. Infected pockets in the wall of the colon. The presence of these may aggravate gas symptoms.
  
  
• Short bowel syndrome. A condition that occurs following the removal of part of the small intestine. Because the small intestine is not long enough to digest food particles, they are passed into the large intestine before being completely digested. Once in the large intestine, fermentation takes place.
  
  
• Gastroparesis. Causes food to pass too slowly from the stomach into the small intestine. Because food remains in the stomach longer, gas symptoms may occur.
  
  
• Abdominal surgeries. People who have had certain abdominal operations or numerous abdominal operations may have more gas problems.  Fundoplication is a surgery that may be used to treat GERD. It often makes it impossible to properly belch, resulting in a condition called gas-bloat syndrome. According to the National Institutes of Health, this occurs in about 10 percent of fundoplication patients. It may improve over time.
  
  
• Meganblase syndrome. A rare syndrome that causes chronic burping. Meganblase syndrome is characterized by swallowing excessive amounts of air and the formation of an enlarged gas bubble in the stomach after consuming a heavy meal.

It is generally recommended that patients seek medical attention for gas symptoms in a number of instances, including:

• Change in the location of abdominal pain
  
  
• Significant increase in frequency or severity of symptoms
  
  
• Onset of new symptoms in patients over 40 years of age
  
  
• Presence of certain accompanying symptoms, including:
  
  
• • Fever
    
    
  • Diarrhea or constipation
    
    
  • Nausea and vomiting
    
    
  • Persistent heartburn
    
    
  • Gastrointestinal bleeding
    
    
  • Unexplained weight loss
    
    
  • Blood in the stool (hematochezia)

Patients whose gas and bloating is accompanied by recurrent, severe or prolonged abdominal pain should notify their physician because this may indicate the presence of another underlying condition – especially if the patient also experiences bleeding, nausea, vomiting, fever or weight loss. The physician will perform a physical examination and compile a thorough medical history. Screening tests, such as an endoscopy, sigmoidoscopy or colonoscopy, may also be conducted to help determine the cause of gas and bloating.

Most gas symptoms that are unrelated to a medical condition are brief in duration. Because of this, gas is often treated by minimizing further symptoms. Problematic gas can often be relieved by identifying and eliminating the factors that cause the gas.

A food diary can be helpful in identifying these factors. A food diary is a journal in which patients carefully track the amounts, the times and the kinds of food consumed and any subsequent gas symptoms. These diaries should be as detailed as possible. Patients are generally recommended to specify the time and conditions under which they eat (e.g., rushed breakfast at 6 A.M., casual lunch at noon). Times, types and severity of gas symptoms also need to be recorded.

Because a large amount of gas is caused by swallowing air (aerophagia), taking steps to avoid swallowing excess air may help reduce gas. Methods to avoid swallowing air include:

• Do not suck on hard candy or chew gum
• Do not gulp beverages
• Do not drink through a straw, out of small-mouthed bottles or from water fountains
• Do not drink during meals
• Do not eat when particularly anxious, upset or in a hurry
• Do not attempt to induce belching
• Eat and drink slowly, with mouth closed
• Make sure dentures fit properly
• Cut down on or quit smoking

Gas and gas symptoms can also be relieved by dietary changes.  Foods that are particularly troublesome for many people include those that contain raffinose. These include many vegetables, especially beans. However, recent research indicates that fermenting beans prior to cooking them eliminates most of their soluble fiber content, thereby reducing their gaseous effects. Milk products and fruits also contain sugars that may be difficult to digest in some people (e.g., lactose, fructose, sorbitol). Patients should discuss any dietary changes with their physician.

It is often recommended that patients cut out or reduce their intake of gas-producing foods. These are different for everyone. For example, a patient may experience gas after eating pears, but not apples. Patients are encouraged to determine precisely which foods are bothersome for them. Cutting back on fat may also help relieve symptoms of gas. This is because a diet high in fat slows the passage of food in the digestive tract, allowing fermentation to take place for a longer time.

Fiber is an important dietary nutrient, but it frequently causes gas symptoms. It is often useful to temporarily cut back on high-fiber foods and then slowly reintroduce them into the diet. This provides the bowels with sufficient time to adjust to the fiber intake. It is also important to drink plenty of liquids with increased fiber intake. In some cases, fiber may actually help ease gas.

Patients are generally encouraged to eat smaller, more frequent meals. This allows the stomach to empty faster and makes digestion easier.

It is often recommended that patients with problematic gas symptoms avoid carbonated beverages. These beverages release carbon dioxide gas. If patients refuse to eliminate these, it may help to pour them in a glass to let some of the “fizz” out.

Some medications and products that may help reduce gas include:

• Digestive enzymes. Help people lacking enzymes to process nutrients that are difficult to digest. Lactase is commonly used to help people with lactose intolerant digest dairy products. Products containing alpha-galactosidase are available to help digest raffinose.
  
  
• Some antacids. Antacids that contain the foaming agent simethicone pool gas bubbles together. Although this has no effect on intestinal gas, it may help with stomach gas. However, antacids that contain bicarbonate or carbonate may worsen gas.
  
  
• Activated charcoal and chlorophyll. Ingredients in many over-the-counter products. The effectiveness of activated charcoal is controversial, but it may help ease symptoms in some people. Both activated charcoal and chlorophyll may help reduce the offensive odor of some gas. However, chlorophyll may turn stools green. Bismuth subsalicylate (a type of antacid) may help to significantly reduce gas odor due to hydrogen sulfide. However, it cannot be taken for more than a few days.

Research also indicates that some medications used to treat diarrhea and constipation may be effective in relieving gas and bloating in some individuals.

It is generally considered best to experiment with only one gas-reducing product at a time. Patients are urged to follow dosing directions carefully and to ask a physician or pharmacist about proper use of prescription and over-the-counter medications.

Preparing questions in advance can help patients to have more meaningful discussions with their physicians regarding their conditions. Patients may wish to ask their doctor the following questions about gas and bloating:

1. I seem to have excessive gas. Is it possible that I am overly sensitive to normal amounts of gas?
   
   
2. What dietary changes may be beneficial for me?
   
   
3. Should I keep a food diary to determine what may be causing my gas symptoms? What if I forget to keep track of everything I eat throughout the day?
   
   
4. How may gas affect my other medical conditions?
   
   
5. Am I lactose deficient or intolerant?
   
   
6. How may my other medications affect my gas symptoms?
   
   
7. Might any of my past surgeries be responsible for some of my gas problems?
   
   
8. Will any of the surgeries I am thinking of having make my gas symptoms worse?
   
   
9. Which gas-reducing products seem best for me? How long should I experiment with these products?
   
   
10. Is there anything I can do to help with the embarrassment of gas symptoms?
    
    
11. Might the combination of my gas symptoms and other symptoms indicate a serious condition?