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Irritable bowel syndrome (IBS)

by ABC Health and Wellbeing

Symptoms of irritable bowel syndrome, or IBS, include constipation, diarrhoea (sometimes alternating), and abdominal pain.

Irritable bowel sydromeiStockphoto

Who amongst us will stand by our bowels when they misbehave?

They can ferment, rumble and explode, not only causing us irritation, but embarrassing us too.

Most of us can live with the occasional abdominal indiscretion. But between one in five and one in ten Australians suffer from more than just a bad bowel day. Their symptoms are severe enough to be given a name – Irritable Bowel Syndrome, or IBS.


People with IBS suffer constipation, diarrhoea (sometimes one alternating with the other), abdominal aches and pains (often relieved by passing a bowel motion), abdominal bloating, and flatulence.

The symptoms can last days or weeks, or may always be there and can seriously interrupt people's work and social lives. Approximately 30 per cent of IBS sufferers take leave from work due to their symptoms.

The causes of IBS aren't fully understood, but the condition is thought to be due to abnormal functioning in the large intestine. Some proposed factors involved in IBS include alterations in the types of bacteria present in the gut, changes in the sensitivity of the nerve endings around the large intestine and the messages they send to the brain, and alterations in the rate in which the muscles contract in the large intestine.

The large intestine (also known as the colon) is a long muscular tube. The muscles in the walls alternately contract and relax, propelling the contents of the bowel forward. Water is absorbed from food waste through the bowel lining, until, by the time they reach the rectum, the contents are firm and ready to be expelled through the anus as faeces. (Nutrients are extracted higher up, in the small intestine.)

In IBS, the movement of these muscles is thought to be uncoordinated. Instead of contracting and relaxing in waves, they contract irregularly and tend to spasm.

Why do the bowel muscles act in this way? Nobody knows for sure.

In the past it was thought to be due to our low-fibre diet, but the condition is just as common in eastern countries where diets are higher in fibre. Particular foods can trigger symptoms, but individuals vary in which foods they are sensitive to. Many studies have now shown convincing evidence of the effect of FODMAPs as triggers for symptoms of IBS. FODMAPs are a collection of short chain carbohydrates (including lactose, excess fructose, fructans, polyols and galacto-oligosaccharides) that can be fermented by the bacteria in the bowel, and can also cause water to enter the bowel. These effects can alter the rate in which the muscles contract.

There also seems to be a neurological component to IBS, and the condition seems to be aggravated by stress, though whether it plays a causative role is controversial.

The bowel is heavily supplied with nerve endings, and it's thought that IBS may be due to a hypersensitivity in those nerve endings – in other words, people with IBS experience more pain from the same level of stimulation than other people. The hypersensitivity may set up a vicious cycle between the bowel and the brain, resulting in bowel symptoms.

Inflammation resulting from infection may also have a role in up to 25 per cent of cases of IBS.

IBS affects twice as many women as men. Though it can occur at any age, it most commonly begins in the twenties or thirties – though again, no-one knows why.


The good news about IBS is that while the symptoms are painful and disruptive, they're not a sign of – nor do they lead to – serious underlying illness.

It's important to see your doctor to make sure it is IBS and not something else. The Gastroenterological Society of Australia advises seeing your doctor if:

  • you have blood in your bowel motions
  • you are over the age of 40 and your symptoms have come on recently
  • you've lost weight
  • you have a family history of bowel cancer.

Your GP will usually have no trouble diagnosing IBS after taking a history and a physical examination. Coeliac disease, inflammatory bowel disease and cancer are amongst the other conditions they will rule out before diagnosing IBS.

To investigate for these other conditions, sometimes the GP will want to do further tests including a blood test, taking a sample of faeces to test for blood, a gastroscopy and a colonoscopy or barium enema.

A colonoscopy is a test performed by a gastroenterologist in which a thin fibre-optic tube is inserted through the rectum and into the colon so that the lining of bowel can be visualised. A gastroscopy is where a thin fibre-optic tube is passed into the mouth, down the oesophagus, past the stomach and into the small intestine. A different tube is used for colonoscopies and gastroscopies. They are performed under light sedation as a day-only procedure in a hospital or private clinic.

If during the procedure there is no evidence of any underlying disease like inflammation of the bowel lining or a tumour, the diagnosis of IBS can be confirmed.


Studies looking into the use of fibre in people with IBS have concluded that increasing fibre intake can worsen symptoms including abdominal distension and flatulence. It is not clear, therefore, that fibre is a helpful treatment for IBS; in fact, there is no single fibre recommendation that is suitable for all people with IBS.

Some studies have shown that a diet low in FODMAPs can help relieve symptoms of IBS in the majority of people who try this diet. FODMAPs are a group of sugars found in many common foods such as dairy, wheat, and some fruits and vegetables. Some people are unable to break down and absorb these sugars; when the undigested sugars enter the large intestine, they are broken down by gut bacteria, which produce gas as a by-product, and also a delivery of water into the bowel.

It is important to commence a low FODMAP diet under guidance of an accredited practising dietitian to ensure that you are not restricting your diet unnecessarily. There are, for example, many fruits, vegetables and grain foods that are low in FODMAPs that you can continue to eat.

At least one well-designed scientific trial has suggested that Chinese herbal medicine can relieve the symptoms of IBS. Conducted by Australian researchers, the study showed that people receiving a mixture of Chinese herbs (either individualised or standardised) had significant improvement in bowel symptoms compared to those receiving a mixture of 'fake' herbs.

You may find that hypnotherapy relieves symptoms of IBS – although there is insufficient evidence that it is effective, it is also free of risk and side effects. Acupuncture may also work for some people, but again, there is no evidence that it is effective.

If the symptoms of IBS are distressing, they can also be relieved with pharmaceutical drugs. Constipation can be treated with laxatives, diarrhoea with an anti-diarrhoeal like loperamide (trade names Imodium, Gastro-Stop), and abdominal pain with anti-spasmodic medications. Certain anti-depressants have also been shown to reduce abdominal pain. Some are available over-the-counter at chemists, others require a doctor's prescription. These remedies relieve the symptoms but they don't correct the underlying condition. It's not a good idea to take them regularly.

This article was reviewed by Dr Sue Shepherd a dietitian and senior lecturer in the Department of Dietetics and Human Nutrition from La Trobe University.

Updated: 24/09/2013

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