Health Check: what causes bloating?

“Bloating”, the feeling of a full and swollen belly, is one of the most common complaints we hear about in medical practice from patients, with 10 to 30% of people experiencing it.

The term is used by patients to describe a wide variety of abdominal sensations, usually associated with abdominal discomfort (feel like one’s going to burst) or tummy cramp. People suffering from bloating may also experience burping, diarrhoea, constipation, abdominal swelling and excessive passing of gas (flatulence).

If we are to understand bloating we need to look at some basic anatomy. The intestinal tract is made up of a hollow tube with a muscular wall. This tube serves different functions in different parts.

The stomach is like a bag that holds food while it mixes with acid to help break it down. The small intestine is long and thin allowing for digestion of food as it mixes with the body’s digestive juices. And the large intestine serves as a reservoir to allow for the final processing of stool.

What causes bloating?

These intestinal organs have nerves in their muscular wall and these nerves are able to sense when the organ is stretched or distended. It is this sensation of over stretching that the body may interpret as bloating. The intestinal organs are enclosed in a cavity that is lined by a membrane (the peritoneum) and this membrane is also able to sense stretching and thus any increase in the overall contents of the abdominal cavity will also be sensed as bloating.

Studies looking at the time taken for intestinal contents to flow through the gut have shown there may be pooling of liquid, gas or solid contents in parts of the gut sensed as bloating. This may be aggravated by the way certain people’s guts sense contents as they may be more prone to the sensation of distension, as may occur in irritable bowel syndrome (IBS).

Although people suffering from bloating often complain of symptoms that may be related to excess gas, it does not seem excess gas on its own is the problem.

Other factors that may be associated with swelling (especially in those who are constipated) includes slow movement of contents in the intestine and weak muscles in the abdominal wall, especially if someone recently gained weight, and a diaphragm muscle that contracts when it should relax.

What can make it worse?

Factors in the diet may well be involved in increasing the risk of bloating, with a small study linking bloating to the consumption of poorly digested sugars. This mechanism may underlie the bloating associated with lactose intolerance and the less commonly diagnosed fructose, fructan (similar to fructose) and sorbitol (corn syrup) intolerance.

The role of the bacteria in the gut (microbiome) in the development of bloating is poorly understood. There are some studies that say there are changes in the bacteria in the gut, especially in IBS. The type of gas the bacteria in the large intestine produce may be linked to bloating.

The gut is under the influence of many hormones, and certain hormones can make a person feel bloated, as is experienced by some women before their menstruation.

Irritable bowel syndrome

Bloating is experienced as part of many conditions, but probably the most common condition associated with bloating is IBS.

IBS is a condition in the family of functional gut disorders (as opposed to those that have a visible structural problem in the intestinal tract). There are two different types, those associated with constipation and associated with diarrohea.

The classic description is that IBS starts early in life and persists over time. Sufferers complain of bloating either after meals or progressively throughout the day. It’s often associated with tummy discomfort that improves with passing stool.

Recent studies in IBS have shown some benefit from a diet that avoids fermentable oligosaccharides, disaccharides, and monosaccharides and polyols (FODMAPs). FODMAPs are types of carbohydrates (sugars) fermented in the intestine by bacteria and increase the fluid content and distension of the gut.

What can you do?

Foods to avoid include those containing onion and garlic and wheat or rye, lactose products such as cow’s milk and stone fruit.

People suffering from other conditions associated with bloating such as lactose intolerance and gluten sensitivity or coeliac disease will need more specific elimination diets.

Since there may be changes in gut flora in IBS, the use of probiotics containing Lactobacillus and Bifidobacteriummay help patients with bloating symptoms by reducing gas production in the gut. This may be particularly useful in children. The use of probiotics has also been found to be effective in those with bloating associated mainly with constipation.

People suffering from bloating should also eat small meals and exercise regularly to improve abdominal wall muscle tone and enhance gas clearance. Being at a healthy weight helps, and in some cases there may be the option of laxatives for those with associated constipation. Abdominal “binders” such as those commercially available to reduce the distended tummy may help. “Anti-gas” remedies seldom have lasting effect but peppermint oil capsules may be helpful.

Certain medications such as antacids, narcotic pain killers, anti-diarrhoeal agents, iron tablets, fibre supplements and stool bulking agents may cause bloating and should be considered the cause if the bloating started soon after their commencement.

Sergio Diez Alvarez does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond the academic appointment above.