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Bloating and Distension: Definitions and Causes

Written by Brian Lacy, MD   

Brian Lacy, MD
Brian Lacy, MD

Symptoms of gas, bloating and distension are quite common. This blog (Part 1 of 2) focuses on the scope of the problem and reviews common reasons for bloating and distension to occur. 

Definition and Common Symptoms

Bloating is a sensation of gassiness (“I feel gassy”), trapped gas, or a feeling feeling of your abdomen being distended or swollen although there may be no obvious visible distension or swelling of the abdomen. Some patients also describe a sense of fullness or pressure in the upper abdomen.  

Abdominal distension describes an observable change in the size of the abdomen with or without the sensation of bloating. Patients commonly say they look “like a balloon” or “like I’m pregnant.” Abdominal bloating and distension are distinct processes although they frequently occur together. Of note, belching and burping are different conditions and develop for completely different reasons.

How Common is this Problem?

Bloating is a common problem. It can affect people of all ages, races, cultures, ethnicities, and nationalities. One survey of U.S. households found that 31% of adults – nearly one in three – had symptoms of gas and bloating.  

Bloating is even more common in disorders such as irritable bowel syndrome (IBS) where up to 60-90% of patients are affected. Bloating and distension are also more common in patients who suffer from chronic constipation, gastroparesis (slow stomach emptying), celiac disease and dyspepsia.

What is Normal?

Everybody makes gas in the intestinal tract, as much as 750-1000 ml of gas each day (the size of a one-liter bottle). In addition, the average person passes gas from the rectum 15-18 times per day. Some people produce gas more frequently than that, often as a result of what they eat.  Bloating and distension may be associated with increased gas but there may also be a normal amount of gas. 

Most gas in the gastrointestinal tract is produced in the large intestine. The large intestine contains a large number of bacteria that help finish food digestion. This can result in gas production, either hydrogen or methane, meaning in some people gas in the intestine may lead to bloating and distension.

What is Abnormal?

There are no agreed upon standards for what is considered abnormal. Certain types of diets create more gas than others. For example, people who take in more protein but only small amounts of fruits and vegetables usually produce less gas than people who eat less protein and  greater quantities of fruits and vegetables.  Also, certain types of foods such as cruciferous vegetables and legumes create more gas than other types of foods. 

In addition, the amount of gas produced reflects the different mixture of bacteria in the colon, and this varies from person to person. In general, health care providers do not focus on the amount of gas produced, but rather the symptoms that are bothersome to the patient. Many people with large amounts of gas do not feel bloated and many with bloating symptoms do not have increased gas.


There are five major causes of bloating and abdominal distension:


Some foods produce more gas and bloating. These include: 

  • Dairy products – milk, ice cream, cottage cheese, cheese 
  • Lactose or milk sugar – for those who are intolerant 
  • High fructose – found in fruits, sodas and energy and sport drinks
  • Cruciferous vegetables – broccoli, cauliflower, cabbage, brussel sprouts  
  • Legumes – red beans, black beans, baked beans, lentils, garbanzo beans, hummus 
  • Onions, garlic and peppers 
  • High fiber foods – fruits, vegetables and whole grains 

While all these items are part of a healthy diet, some patients can produce more gas and bloating than other types of foods or consume larger quantities than usual.

Disorders of Intestinal Transit 

Disorders that affect how materials move through the gastrointestinal (GI) tract, including irritable bowel syndrome with constipation (IBS-C) or chronic or functional constipation, commonly may lead to bloating and distension. Many patients with these symptoms also have difficulty evacuating gas and this can lead to symptoms of gas and bloating as well.

Small Intestinal Bacterial Overgrowth (SIBO)

Normally, very few bacteria live in the small intestine. Patients who have SIBO have a problem with too many bacteria living in the small intestine. These bacteria process food sooner than usual and this can cause symptoms of gas and bloating.

Abnormal Bowel Sensitivity (Visceral Hypersensitivity)

Sometimes it is not how much gas there is but how sensitive the bowel is to the gas that is stretching the intestines. Simply stated, some people sense very low levels of pain or gas sensation related to the presence of gas that others don’t feel.

Gut-Brain Dysregulation (Abdominophrenic Dyssynergia)

This is a disorder related to how the brain coordinates the muscles of the abdominal wall with the intestinal tract.  Normally, when gas in the intestinal tract stretches the stomach, small intestine or large intestine (often after eating a meal), it signals the brain to cause the muscles of the abdominal wall to automatically contract so that the abdomen does not bulge out. 

Contraction of the abdominal wall muscles will minimize symptoms of distension. However, in some patients this automatic contraction does not occur, and in fact, the brain inappropriately sends down nerve signals to relax rather than contract the abdominal wall and to also push down the diaphragm. As a result, your abdomen may become more distended. Why this occurs in some patients but not others is unknown.

In Part 2 of this blog, I’ll cover the diagnosis process as well as treatment options for bloating and distension. In the meantime, you can refer to my online discussion with Dr. Drossman and Johannah Ruddy M. Ed. for more information.

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