For many patients with irritable bowel syndrome (IBS) and functional gut disorders, one of the most bothersome symptoms is bloating (1,2), a sensation of increased abdominal pressure.
Around 50% of patients with bloating also experience distension, an increase in abdominal girth of up to 10cm. Distension can be particularly intrusive, causing many sufferers to avoid wearing certain clothes and not attend social events due to their appearance (3).
What are the causes of bloating?
The causes of bloating and distension are often multifactorial, individuals may have one or more underlying cause for their symptoms. Although overlapping, research has shown the bloating and distension to have differences in their pathophysiology. Hypersensitivity in the abdomen plays a major role in bloating, and has a great association with diarrhoea-predominant IBS subtype (IBS-D). Distension is more commonly associated with constipation-predominant IBS (IBS-C), often caused by slow intestinal transit (4).
The handling of gas in patients with IBS has been shown to be impaired compared to healthy individuals. In a study looking at gas handling it was shown that IBS patients retained far more gas in the abdomen than healthy volunteers and symptoms of bloating and distension were associated with gas retention (5). Individuals who have problems defecating also exhibit greater bloating and distension, likely due to impaired evacuation of gas and stool (6).
When the volume in the intestines changes, due to gas or food, the abdominal cavity adjusts, this is called the accommodation reflex. One study showed when abdominal volume was increased by gas infusion in healthy volunteers, the abdominal cavity accommodated for this by contracting internal oblique muscles and relaxing of a diaphragm (7). However, the mechanism for accommodation in patients complaining of bloating and distension appears to be paradoxical to the normal response. In this group of patients, contraction of diaphragm and relaxation of the internal oblique muscles was seen, associated with significantly more abdominal distension than healthy volunteers (8).
Bloating is also seen in patients suffering from small intestinal bacterial overgrowth (SIBO). In healthy individuals, there is a much smaller concentration of bacteria in the small bowel compared to the colon. When gut bacteria over-proliferate the small bowel they can begin to ferment ingested nutrients before our body absorbs them, referred to as SIBO. The by-products of this fermentation (gases, water and short chain fatty acids) can then lead to symptoms of bloating, diarrhoea and abdominal pain (9).
Carbohydrate malabsorption can also cause bloating, the most commonly described being lactose malabsorption (Hypolactasia). Lactose is the sugar found in dairy products, it is a disaccharide meaning it is made up of two simple sugars (monosaccharides), glucose and galactose. Hypolactasia is a condition where the enzyme lactase becomes depleted in the small bowel. Lactase is required to break down lactose into the two simple sugars before they can be absorbed. If lactase is depleted this process will be impaired leading to fermentation of lactose in the colon, causing bloating amongst other abdominal symptoms. Hypolactasia has a higher prevalence Eastern, African, South American populations compared to European populations (10).
Even in healthy individuals it is normal for some carbohydrate to enter the colon where they are fermented. These sugars are known as Fermentable Oligosaccharides, Disaccharides, Monosaccharides, and Polyols (FODMAPs). Where an imbalance of colonic bacteria occurs (dysbiosis), as seen in patients with an irritable bowel (11), there may be altered fermentation of these carbohydrates in the proximal colon. The production of increased short chain fatty acids as a by-product of colonic fermentation may cause changes to the pH of the gut and altered gut motility (12). These changes to the environment and motility of the gut in addition to the gases produced as by-product of fermentation may ultimately contribute to bloating and distension.
How can bloating and distension be treated?
Understandably, these symptoms can significantly affect quality of life, so an effective treatment could make a big difference to many IBS patients. Due to the diversity of causes of bloating and distension, treatment will be specific to the underlying causes of bloating. However, a range of methods have been shown to alleviate symptoms for some patients, including dietary modification, medications and physical therapies.
How can Small Intestinal Bacterial Overgrowth (SIBO) be detected and treated?
A simple breath test may detect if SIBO is responsible for bloating. If positive, specific antibiotic regimes can decrease the bacterial count in the small bowel. By reducing levels of small intestinal bacteria, premature fermentation of ingested foods is reduced, thus alleviating symptoms of bloating.
Can probiotics help to reduce bloating and distension?
If SIBO is not the cause of symptoms other therapies may be considered. As gut microbiota may differ in irritable bowel syndrome to those in healthy individuals, alteration of the microbiota with probiotics is a potential target for alleviation of bloating and distension. One study demonstrated that the daily intake of a probiotic yoghurt (Bifidobacterium lactis) alleviated distension in patients with IBS-C through acceleration of intestinal transit (13). In another study, a combination probiotic (VSL#3) was shown to reduce the symptom of bloating in a proportion patients and slow colonic transit (14). Despite positive results from several studies, further research into different types of probiotics (species, mixtures, strains), optimum dosage and treatment length are required to better understand the role of probiotics and their effect on bloating and distension. When trialling probiotics, individuals should only use one probiotic at a time allowing them to evaluate the effect of the probiotic on their symptoms more accurately. Individuals should follow manufacturers/healthcare professionals’ dosage instructions and consume for at least 4 weeks (15).
Can a change in diet help to reduce bloating?
Introduction of a low FODMAP diet may help relieve symptoms by removing these highly fermentable sugars from the diet, thus reducing fermentation. These troublesome sugars are found in foods such as onions, garlic, dairy and some fruits. A low FODMAP diet can be quite restrictive and therefore should be undertaken with the guidance of a dietician. The dietician will be able to guide patients on which foods they need to initially restrict, as well as manage the reintroduction of foods to make sure there are no shortfalls in the patients’ nutritional intake.
Breath tests can also be carried out to assess whether individuals are mal-absorbing specific sugars such as lactose and fructose. By finding out if certain sugars are being mal-absorbed it is possible to tailor diets to reduce bloating caused by fermentation of these specific sugars. A wireless motility capsule (Smartpill) can also be utilised to assess the motility and pH gastrointestinal tract to look signs of fermentation and potential causes of bloating.
What is Faecal Microbiota Transplantation (FMT)?
There is increasing public and media interest around the topic of FMT and its potential uses. FMT is the process of collecting faeces from a healthy donor, separating the gut bacteria (microbiota) from other faecal matter and transplanting the microbiota into another individual with a disease or disorder relating to the microbiota. The aim of this process is to repopulate the gut of the diseased individual with the microbiota of the healthy individual and thus treating the underlying cause of the disease. FMT is most effective treatment for recurrent Clostridium Difficile (16) and research is showing promise in other conditions such as ulcerative colitis (17). A great deal more research is needed to establish the effectiveness and safety of FMT in other conditions including IBS and this will certainly be a hot topic in coming years.
Are there any medications which can help alleviate bloating and distension?
Antidepressants at a relatively low dose can be used to target bloating; studies have shown that Citalopram can significantly reduce symptoms of bloating through its effect on improving bowel motility and regularity (18). Other antidepressants such as amitriptyline are also known to improve stool consistency and reduce hypersensitivity of the gut (19), thus reducing the sensation of bloating.
Other medications have a more specific effect on the bowel; the drug Linaclotide increases transit time and reduces visceral hypersensitivity via activation of the enzyme guanylate cyclase C and has been shown to reduce the symptom of bloating and in patients with IBS-C (20).
The medication Ebastine, an antihistamine has been shown to relieve bloating and distension among other IBS symptoms in a recent clinical trial. It works by desensitising the TRPV1 pain receptor, where typically histamine and its metabolites bind, contributing to visceral hypersensitivity (21).
Are there any physical therapies that can be used to reduce distension?
Biofeedback is a clinical tool used by clinicians and physiotherapists to reduce distension. One study demonstrated the effectiveness of biofeedback by comparing participants with distension to healthy volunteers (22). Through electrodes attached to the skin, respiratory targeted biofeedback helped to reduce the activity of the diaphragm (by 18% ± 4%) and intercostal muscles (by 19% ± 2%) and increased the activation of the internal oblique muscles (by 52% ± 13%). An average reduction in abdominal girth of 25mm was seen in these patients following this biofeedback technique.
Biofeedback can be utilised in patients with defecatory disorders to improve evacuation technique, thus reducing bloating and distension. In order to pass stool, it is important to relax the muscles in the back passage. Some individuals inadvertently contract the muscles in back passage, which acts as a barrier to the passage of stool, known as dyssynergic defecation. Pelvic floor targeted biofeedback conducted by a trained physiologist or physiotherapist can help individuals to visualise their bad toileting technique and correct it.
Although there is a large range of treatment options targeting the various causes of bloating and distention in IBS patients, they will not all work for everyone. It is important to identify the underlying mechanisms and contributing factors behind the symptoms on a case by case basis to select the most effective treatment for each patient.
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