What Causes Bloating and Gas?

People with Inflammatory Bowel Disease (IBD), which includes Crohn’s Disease and Ulcerative Colitis (UC), often report feeling bloated. Many also worry about excess gas and its effects, such as tummy gurgles and flatulence (breaking wind).

What causes bloating and wind?

There are several possible explanations for bloating and wind. A major cause of bloating is gas. Gas can be trapped in the body to cause bloating, or can be expelled as wind (flatulence) (see below). 

Bloating is also a common symptom of Irritable Bowel Syndrome (IBS). This is a separate condition from IBD, but both UC and Crohn’s make it more likely that you may also have IBS. For example, an attack of UC may be followed by irritable bowel symptoms, including bloating, which may last for several months.


It has been suggested that bloating is more likely to occur if you have constipation. Eating a lot of fatty food can delay stomach emptying, and this too may cause bloating and discomfort. You may also experience bloating if you have adhesions (scar tissue) as a result of previous surgery.

What causes gas? 
It is normal to have gas in your intestine whether or not you have IBD. We all produce several litres of gas a day through the normal processes of digestion. Some of this is reabsorbed into the bloodstream and eventually breathed out. The remainder has to be expelled as wind. Most of us probably break wind some 15 – 40 times a day, even if we are unaware of it.


One possible cause of excess gas may be swallowing too much air when eating, drinking or talking (aerophagia). Certain foods and fizzy drinks can also contribute to this. Smoking can also make you swallow more air. Some people swallow air as a nervous reaction.

Excess gas can also be caused by bacteria in the colon producing too much gas when they break down food. Foods containing complex carbohydrates, for example vegetables such as beans, cabbages and Brussel sprouts, are difficult for the human body to digest. They are broken down by the gas-producing bacteria instead. Foods that contain sorbitol, an artificial sweetener, can lead to similar problems. Poor digestion and absorption of food in the small intestine (often a feature of Crohn’s Disease) can also mean that more undigested food reaches the colon, and can cause even more gas.


Lactose intolerance (difficulties with digesting lactose - a sugar found in milk) can also cause gas. You may become lactose intolerant if you lack the enzyme lactase, meaning that you cannot break down the lactose. Instead, it is fermented by the gas-producing bacteria in the colon. Research has shown that people with Crohn’s in their small intestine are more likely to be lactose intolerant. People with UC have the same chance of being lactose intolerant as the general population.

It has also been suggested that some people may simply have more bacteria than others, or bacteria that produce more gas.