Symptoms of irritable bowel syndrome (IBS) will be experienced by one in five Australians during their lifetime, affecting women more often than men. It is important to note IBS does not cause lasting damage to the bowel or contribute to the development of more serious conditions, such as bowel cancer or colitis. The symptoms of IBS, however, are unpleasant and affect the sufferer’s quality of life.

The onset of IBS often occurs in early adulthood; it is unusual for symptoms to first appear after 40 years of age. Symptoms of IBS include abdominal pain or cramping (which are often relieved by passing wind or faeces), abdominal bloating or distension, nausea, mucus in stools, altered stools (e.g. lumpy, hard, pellet-like, unformed), alternating diarrhoea and constipation, altered stool passage (e.g. straining or urgency), changes to frequency of defecation (more than three motions per day or less than three motions per week) and a sensation that bowels are not fully emptied after passing a motion.

There are three main categories of IBS: constipation predominant, diarrhoea predominant, and alternating between constipation and diarrhoea.

Causes of IBS

The causes of IBS are poorly understood, although it is thought intestinal dysmotility (abnormal contractions in the small and large bowel), visceral hypersensitivity, and psychosocial factors may contribute to symptoms through pathways mediated by serotonin and other enteric nervous system transmitters. Visceral hypersensitivity occurs when gastrointestinal processes (which are not normally perceived by individuals) are consciously experienced, and may be perceived as painful. A post-infective form of IBS exists where there is persistent inflammation of the colonic mucosa. This accounts for approximately 25% of diagnosed IBS cases. Strong emotions such as anxiety or depression can also affect the nerves of the bowel in susceptible people, causing IBS symptoms.

Food intolerances can trigger IBS and are usually the result of the impaired absorption of sugars found in foods. FODMAP is an acronym for fermentable oligosaccharides, disaccharides, monosaccharides and polyols; which are a group of sugars that are poorly absorbed by some people. When sugar molecules are poorly absorbed in the small intestine, they continue along the digestive tract, where they become a food source for the bacteria that colonise the large intestine.

The bacteria digest and ferment these sugars which can cause IBS symptoms. Examples of these sugars are fructans and galactans (oligosaccharides), lactose (disaccharide), fructose (monosaccharide), sorbitol, mannitol, maltitol, xylitol and isomalt (polyols). Other dietary triggers may include fat, fibre, alcohol and caffeine.

Medications may also cause symptoms similar to IBS, such as constipation or diarrhoea as a side-effect. These symptoms are generally resolved if the offending medication is ceased or changed to another agent without the same side-effect profile.

Diagnosis of IBS

Diagnosing IBS is difficult as the symptoms experienced are not exclusive to IBS. Other illnesses such as diverticulitis, inflammatory bowel disease, coeliac disease, and polyps should be excluded. This may involve blood tests, stool tests and investigation of the bowel lining (by sigmoidoscopy, colonoscopy or barium enema).

For a diagnosis of IBS to be made the patient must have the presence of unexplained abdominal discomfort or pain for at least 12 weeks in the last 12 months (not necessarily consecutive), with at least two of the following three features:

  • Pain is relieved by defecation
  • Onset of pain is associated with a change in bowel frequency (either diarrhoea or constipation), or
  • Onset of pain is associated with a change in the form of the stool (loose, watery
    or pellet-like).

Due to malabsorption of sugars, some food intolerances can be identified by breath hydrogen methane testing (more information can be found here); this can be useful if food intolerance is the suspected cause of symptoms.

Treatment of IBS

There is no cure for IBS, and treatment involves identifying and avoiding triggers. This can include stress management, dietary, and lifestyle modification. Some people with IBS have associated depression or anxiety, the recognition and treatment of which may lead to the resolution of abdominal symptoms. Medications are helpful only for the minority of patients and are used to manage symptoms.

Identifying dietary triggers of IBS can be difficult, as the time taken for symptoms to appear after an offending food has been ingested varies, and is not always immediate. Symptoms may also last for some days. The process of identifying causative foods is best done under the supervision of a dietician. This usually involves keeping a food and symptom diary, and a systematic process of eliminating and reintroducing foods one at a time to see how symptoms respond.

If causative foods are identified, sufferers can reduce or eliminate their intake of these to reduce symptoms. Other dietary measures include reducing dietary intake of known gas producing food such as beans, lentils, brussel sprouts, onion, cauliflower and cabbage.

A minority of patients with IBS respond to medication. For exacerbation of diarrhoea the Therapeutic Guidelines: Gastrointestinal recommends trialling loperamide or cholestyramine. Other references also recommend trialling Lomotil® (diphenoxylate and atropine).

The Therapeutic Guidelines: Gastrointestinal recommends symptoms of constipation be treated in the same way as constipation in general. Initial measures are increasing dietary fibre, fluid intake and exercise. Laxatives which increase the bulk of the stools, stimulating the bowels to open, may be trialled if initial measures prove ineffective. These include Agiofibe®, Fybogel®, Metamucil®, and Normafibe®. It is important the patient also has an adequate fluid intake to avoid stools becoming hard.

Bulk-forming agents are not always effective, even for mild constipation, and may increase flatulence and bloating for some patients. Osmotic laxatives (e.g. sorbitol [check for malabsorption of polyols], lactulose, or macrogol) work by drawing water into the stools, which expand and soften them. These are a good choice, particularly where frequent use appears necessary.

Stimulant laxatives can be effective either alone (e.g. bisacodyl, or senna) or in combination with a softener (e.g. Coloxyl® with senna). These work by stimulating intestinal motility, but can cause or exacerbate abdominal cramps. Stool softeners as monotherapy have no proven effectiveness. Suppositories and enemas are usually reserved for faecal impaction. The prolonged use of any laxative should be avoided where possible.

Antispasmodic drugs may help to control abdominal pain and occasionally diarrhoea. The Therapeutic Guidelines: Gastrointestinal recommend:

  • Hyoscine butylbromide 20mg orally four times a day when required
  • Mebeverine 135mg orally three times a day when required, or
  • Peppermint oil (0.2mL/capsule) one to two orally, three times a day when required
    (30 minutes before food).

There is some evidence to support the use of tricyclic antidepressants and selective serotonin reuptake inhibitors in decreasing IBS pain. Tricyclic antidepressants may also cause constipation, drowsiness and anticholinergic side-effects, which may limit their use.

The Therapeutic Guidelines recommend:

  • Amitriptyline 10-25mg (orally) daily at night
  • Nortriptyline 10-25mg (orally) daily at night
  • Citalopram 20mg daily, or
  • Fluoxetine 20mg daily.


Irritable bowel syndrome involves a range of unpleasant gastrointestinal symptoms. There are many triggers, and much regarding the pathophysiology of IBS remains unknown. Diagnosis is made by a medical practitioner, after assessing the patient using defined criteria and ruling out other causes of symptoms.

Treatment involves the identification and removal of triggers. Some food intolerances can be tested for and managed by a dietician. Medications may have a role in symptom relief for some sufferers.

Further reading:

  1. Gibson PR, Shepherd SJ. Evidence-based dietary management of functional gastrointestinal symptoms: The FODMAP approach. J Gastroenterol Hepatol. 2010; 25(2):252-8.
  2. Shepherd SJ, Parker FC, Muir JG, Gibson PR. Dietary triggers of abdominal symptoms in patients with irritable bowel syndrome: randomized placebo-controlled evidence. Clin Gastroenterol Hepatol. 2008; 6(7):765-71.


  1. Digestive Health Foundation. Irritable Bowel Syndrome. 2nd ed. Sydney: Gastroenterological Society of Australia; 2003.
  2. Gastrointestinal Expert Group. Therapeutic Guidelines: Gastrointestinal. Version 5. Melbourne: Therapeutic Guidelines Limited; 2011.
  3. Irritable Bowel Information & Support Association of Australia Inc. IBIS Irritable Bowel Information. Forest Lake, Australia. Available from Accessed 13 Mar 2014.
  4. Shepherd Works. Hydrogen Breath Testing. Box Hill: Shepherd Works; 2014. Available from: Accessed 13 Mar 2014.
  5. Shepherd Works. Low FODMAP Diet. Box Hill: Shepherd Works; 2014. Available from Accessed 13 Mar 2014.

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