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)