Abdominal Bloating - Is it just gas?

Key Points

  • Bloating is a common presenting symptom of functional gastrointestinal (GI) disorders, occurring either in isolation (functional bloating) or as part of a disorder such as irritable bowel syndrome (IBS.)
  • Patients often use the term loosely to describe associated symptoms such as belching, borborygmi and excessive flatus, as well as subjective abdominal distension.
  • The underlying pathophysiological mechanisms for bloating are difficult to define but may involve a combination of retained intraluminal gas, altered GI motility and visceral hypersensitivity.
  • Functional bloating and bloating as a manifestation of IBS can usually be diagnosed clinically, but judicious use of investigations to exclude organic pathology should be considered, especially patients who present with ‘red flag’ symptoms.
  • Management of functional bloating is often challenging; an initial trial of lifestyle and dietary modification is generally recommended. A diet low in FODMAPs (Fermentable Oligosaccharides, Disaccharides, Monosaccharides, and Polyols,) has good evidence in efficacy in the management of IBS.

Abdominal bloating is a common problem seen in general practice. It is a term used to describe the subjective sensation of abdominal fullness with or without actual increase in abdominal girth.

The cause of abdominal bloating is usually functional in nature, but investigations to exclude important organic causes may be needed, depending on age of symptom onset and other associated symptoms and signs.

Patients commonly use this term loosely to describe abdominal symptoms such as belching, borborygmi and excessive flatus, as well as subjective abdominal distension. Abdominal bloating is common, with some data suggesting that almost 20% of the general population experiences abdominal bloating at some stage.

Abdominal bloating is a frequent complaint in patients with Functional Gastrointestinal (GI) Disorders, occurring either in isolation –Functional Abdominal bloating/distension – or as part of another functional bowel disorder, such as Irritable bowel syndrome (IBS.)

Functional GI disorders are now described as Disorders of the Gut- Brain Axis, which puts more emphasis on a patient’s reporting of an illness experience rather than it being purely a problem of the GI tract. Patients often attribute abdominal bloating solely to the accumulation of intestinal gas, but other factors such as psychological factors, changes in intra-abdominal sensations and visceral reflexes play an important role.

Mechanisms of bloating

Intestinal production of gas:

The gut microbiome is vital for maintenance of GI function and integrity. Gut bacteria produce gas by fermenting complex carbohydrates and nonabsorbable fibre. Although carbon dioxide is rapidly absorbed in the upper GI tract, it may contribute to bloating in patients with visceral hypersensitivity. Hydrogen and methane are produced mainly in the colon by fermentation of food residue by the gut bacteria.

Altered gastrointestinal transit:

Slowed transit of food matter may cause bloating by several mechanisms. Firstly, it can lead to stasis and a physical increase in the intraluminal content. Secondly, slowed transit may lead to small bowel bacterial overgrowth (SIBO,) which can cause an imbalance in the quantity and distribution of bacteria.

Visceral hypersensitivity:

Visceral hypersensitivity refers to how the central nervous system (CNS) interpret changes in total abdominal content and girth. Signals from the abdomen, such as changes in abdominal wall muscle tone, are important in the perception of bloating.

Gut–Brain Axis:

These interactions are complex. It is believed that abdominal symptoms can influence anxiety and depression, and vice versa.

Investigation of bloating

A thorough clinical history and physical examination are needed to clarify what the patient means by bloating and to ensure that organic disease is excluded before bloating can be considered to be functional. How to investigate a patient with bloating is large dependent on the patient’s age and rapidity of symptom onset.

Coeliac disease:

 IgA antibodies to tissue transglutaminase (TTG) and deamidated gliadin peptide have good sensitivity and specificity for the diagnosis of coeliac disease. Total IgA should also be measured, as 1-2% of patients with coeliac disease also have selective IgA deficiency.

Abdominal imaging:

Ultrasound is useful for the assessment of biliary, ovarian pathology and ascites. CT scans are also useful for the diagnosis of solid organ malignancies.

Stool microscopy and culture:

Stool microscopy and culture are important for patients with an acute diarrhoea that has lasted more than a few days. Salmonella, campylobacter and giardia can cause bloating before the onset of diarrhoea.

Faecal calprotectin:

Calprotectin is a protein released from neutrophils in response to inflammation or infection of the GI tract. Measurement of faecal calprotectin is useful for differentiating inflammatory bowel disease from IBS as a simple non-invasive test.


Peptic ulcer disease, gastric outlet obstruction and sinister upper GI causes should be ruled out with endoscopy.  Patients are encouraged to have small amounts of gluten in their diet just prior to their gastroscopy to increase the diagnostic yield of duodenal biopsies for coeliac disease. Colonoscopic evaluation should be considered to exclude inflammatory bowel disease, microscopic colitis and colorectal malignancies.

Management of bloating

Patients with bloating symptoms attributed to IBS usually involves control of associated symptoms such as pain, abdominal cramps, constipation and diarrhoea. Whilst the overall evidence base for most pharmacological treatments including prokinetics and surfactants such as simethicone is generally weak, a short trial of various interventions is useful, nonetheless.

Lifestyle modification:

Bloating can be associated with eating habits, such as eating too quickly, while ‘on the go’ or watching television. Patients should be encouraged to identify the particular trigger themselves, whether it be the type of food, the style of eating or stress. This allows patients to adapt to behavioural changes and avoidance of specific dietary triggers.

Dietary modification:

FODMAPS: FODMAPs are poorly absorbed short- chain carbohydrates that are thought to give rise to abdominal symptoms through osmotic effects and gas production via bacterial fermentation. A low FODMAP diet is actually a 2-phase intervention: strict removal of all FODMAPs and then slow reintroduction of specific FODMAP groups depending on patient tolerability. Engagement of an experienced dietician is important. A diet that is low in FODMAPs appears to be a reasonable first-line management in patients with bloating pending a further review in a few weeks’ time.

Pharmacological therapy:

Antispasmodics: Antispasmodics have been shown to be of some benefit in the treatment of abdominal bloating and IBS type symptoms However, they should only be used for short-term relief of symptoms. Examples include hyoscine (Buscopan) and mebeverine (Colese.)

Prokinetics: Newer agents such as prucalopride (Resotrans,) which is a selective serotonin (5HT4) agonist, have been shown to be effective in idiopathic chronic constipation.

Complementary medicine: Variable benefit is seen with the use of peppermint oil, Iberogast (STW5, a proprietary herb mixture) and selected probiotics in functional GI disorders.

Despite being a common complaint, abdominal bloating is probably one of the most poorly understood GI symptoms. Treatment of bloating needs to be individualised for each patient and generally involves a combination of lifestyle and dietary modifications, followed by a short-term trial of various pharmacological therapies.


Dr James Pang is a Gastroenterologist providing care in Chatswood, Sydney’s Lower North Shore & the surrounding areas. 

Dr Pang obtained his medical degree from the University of NSW before completing his gastroenterology training at St George and Campbelltown Hospital. He became a Fellow of the Royal Australian College of Physicians (FRACP), before obtaining his Masters in Medicine through the University of Sydney. Dr Pang then spent two years working abroad in Hong Kong as a clinical research fellow, focusing on viral hepatitis (Hepatitis B and C) and non-alcohol fatty liver disease. He is a Conjoint Committee accredited endoscopist (gastroscopy and colonoscopy) and a member of the Gastroenterological Society of Australia (GESA).  

Dr Pang is passionate about education and training of future generation of doctors. He is actively involved in medical education and is a College supervisor of gastroenterology advanced trainees at Gosford Hospital. He is a conjoint lecturer at the University of Newcastle.