Irritable bowel syndrome

What IBS is

Irritable bowel syndrome is one of the commonest reasons people see a gastroenterologist. It is now classed as a disorder of gut-brain interaction: the bowel is structurally normal, but the nerves, muscles and signalling between the gut and the brain are working differently, so that normal amounts of gas and movement are felt as pain, bloating and urgency, and the bowel moves too fast, too slowly or both.

It is diagnosed on the pattern of symptoms. The internationally used Rome IV criteria describe recurring abdominal pain, on average at least one day a week over the last three months, related to opening the bowels or to a change in how often or what the stools look like. IBS is further divided into constipation-predominant, diarrhoea-predominant and mixed types, because the treatment differs.

Triggers are often identifiable: a bout of gastroenteritis, stress, disrupted sleep, hormonal changes and certain foods.

It is common, and how common depends on which definition is used. healthdirect puts it at around one in five people, while a large international study across 33 countries found about 4 to 10 per cent, depending on which set of diagnostic criteria was used. It is more common in women, it often starts in the twenties or thirties, and it can begin at any age. Being common does not make it trivial. For most people the symptoms are mild to moderate, for a smaller number they are disabling, and for many they decide where you sit in a meeting and whether you take the trip.

What are the symptoms, and what are the three types

The core of IBS is abdominal pain that is tied to the bowels: it eases or worsens when you open them, or it arrives when the pattern changes. Around that sit bloating and visible distension, wind, urgency, straining, a feeling that the bowel has not emptied and mucus in the stool. Many people also have tiredness, nausea, reflux or upper abdominal fullness, and these overlap far more often than people are told.

The type matters because it decides the treatment. It is set by what the stools look like on the bad days, using the Bristol stool scale, which runs from hard pellets at one end to liquid at the other.

• IBS with constipation, where hard or lumpy stools dominate, often with straining and incomplete emptying
• IBS with diarrhoea, where loose or watery stools dominate, usually with urgency and sometimes with several bowel actions in the first hours of the day
• Mixed IBS, which swings between the two, sometimes within the same week

The type can change over the years, and treatment changes with it. It is worth saying plainly that symptoms which sound alarming to the person having them, such as severe pain or ten bowel actions in a morning, are not in themselves a sign of something more serious. What matters are the warning features set out below.

Why it happens

There is no single cause, and the honest answer is that several things combine differently in different people.

• A more sensitive gut. The nerves of the bowel report normal amounts of gas and stretch as painful. This is called visceral hypersensitivity and it is the best understood part of IBS.
• Altered movement. The bowel squeezes too hard or too weakly, which produces urgency at one end of the spectrum and constipation at the other.
• After an infection. A bout of gastroenteritis can leave the gut altered for months or longer.
• The gut bacteria. The mix of organisms in the bowel differs in IBS, although it is not yet clear how much of that is cause and how much is consequence.
• The gut and brain loop. The two are in constant two-way communication. Stress, poor sleep and anxiety do not create IBS out of nothing, but they turn the volume up, and months of unpredictable symptoms then feed the anxiety back.
• Family and early life. IBS runs in families to some degree, and early life events including severe gut infections appear to matter.

One finding is worth setting out, because it changes how the condition should be thought about. Anxiety and low mood occur more often in people with IBS, and the old explanations ran in one direction or the other: either the worry caused the gut symptoms, or years of gut symptoms caused the worry. Large genetic studies point somewhere else. Several of the same gene variants turn up in both IBS and anxiety disorders, which suggests a shared underlying susceptibility affecting the nerves of the gut and the brain rather than one causing the other. A 2023 review in Molecular Psychiatry sets out the evidence for this and for the wider brain, gut and microbiome model.

None of this is the same as the symptoms being imagined, and none of it means there is nothing to treat. It is the reason treatment works at several levels at once: the food going in, the nerves and muscles of the bowel, and the signalling between the gut and the brain.

What needs to be ruled out

The most important part of the first consultation is making sure nothing else is going on. Usually a small number of tests is enough:

• a full blood count and iron studies, to look for anaemia or iron deficiency
• a blood test for coeliac disease, which can look exactly like IBS
• a stool test called faecal calprotectin, which is raised in inflammatory bowel disease and normal in IBS
• stool tests for infection where diarrhoea is prominent

A colonoscopy is not needed for everyone with IBS. It is recommended where there are warning features: bleeding, weight loss, iron deficiency, a raised calprotectin, symptoms that wake you at night, or a family history of bowel cancer or inflammatory bowel disease. Persistent watery diarrhoea may also warrant biopsies to look for microscopic colitis, which causes similar symptoms and is treated differently.

Those features count at any age. Symptoms that begin after 45 add to the case for looking, and being younger does not take away from it. Bowel cancer under 50 is rising in Australia, so a young person with bleeding or iron deficiency needs the same explanation as an older one. There is more on bowel cancer under 50.

Conditions that look like IBS

Several conditions produce the same symptoms and are treated quite differently, which is why the first consultation is mostly listening and then testing selectively.

• Coeliac disease, which is why the blood test is done before anyone removes gluten. Cutting gluten first makes the test unreliable.
• Bile acid diarrhoea, where bile that should be reabsorbed reaches the colon. In a meta-analysis of six studies and 908 people with diarrhoea-predominant IBS, about 28 per cent had evidence of it. It responds to a specific medicine rather than to IBS treatment.
• Microscopic colitis, which causes watery diarrhoea and is found only on biopsies taken at colonoscopy.
• Inflammatory bowel disease, which is what the faecal calprotectin test is for.
• Persistent infection such as giardia, particularly after travel.
• Pelvic floor dysfunction, where the muscles do not relax to let stool out. This causes straining and incomplete emptying and is treated by a pelvic floor physiotherapist rather than with laxatives.
• Endometriosis, which commonly presents with bowel symptoms and is often diagnosed years late.
• Thyroid disease, and side effects of medicines, which are easy to check and easy to miss.

Which dietary changes help

Food does not cause IBS, but it often affects symptoms. The usual mistake is to start with the most restrictive diet available. Simpler changes are worth a few weeks first, and they are enough for a good number of people.

• Regular meals rather than long gaps and then a large meal.
• Enough fluid, and a realistic look at coffee, alcohol, fizzy drinks and very fatty or spicy food, all of which speed the bowel up or provoke cramping in some people.
• Fibre adjusted by type rather than simply increased. Soluble fibre such as psyllium and oats helps constipation, while a lot of insoluble fibre such as bran can make bloating worse. healthdirect suggests 25 to 30 grams of fibre a day for adults, built up slowly.
• Eating slowly, which sounds trivial but reduces swallowed air and post-meal distension.

The low FODMAP diet

The low FODMAP diet was developed at Monash University in Melbourne. It reduces a group of fermentable carbohydrates found in foods such as onion, garlic, wheat, some fruits and legumes, which draw water into the bowel and are fermented by gut bacteria. Monash reports that symptoms improve in three out of four people who follow it.

It is a three-stage process, not a way of eating for life.

1. Restriction, two to six weeks, long enough to know whether it is working.
2. Reintroduction, adding the groups back one at a time to find which ones actually matter to you, because most people react to some and not others.
3. Personalisation, a long-term diet that avoids only your own triggers and is as broad as it can be.

Stage one is the part people find online and the part they get stuck in. A strict diet followed indefinitely narrows what someone eats, affects the gut bacteria and makes eating out and family meals miserable, which is a real cost. This is why it works best with a dietitian experienced in IBS and why the reintroduction stage matters as much as the restriction.

What is not worth your money

Commercial food intolerance blood tests, usually sold as IgG testing, are not supported by evidence and lead people to cut out foods they do not need to. Long-term elimination of whole food groups without a reason has the same problem. If gluten seems to be a trigger, have the coeliac blood test before removing it, not after.

What medication and gut-brain therapies do

Medication is chosen by the main symptom rather than the diagnosis:

• Constipation: soluble fibre, osmotic laxatives and newer prescription medicines when those are not enough.
• Diarrhoea and urgency: anti-diarrhoeal medicines and in some cases medicines that bind bile acids.
• Pain and cramping: antispasmodics such as peppermint oil, and low doses of certain antidepressants, which are used here for their effect on gut nerves rather than on mood, and work at doses well below those used for depression.

Gut-directed psychological therapies, including gut-directed hypnotherapy and cognitive behavioural therapy, have good evidence in IBS and change how the gut and brain communicate. They are offered because they work, not because the symptoms are thought to be in anyone's head.

Gut-directed hypnotherapy can also be done at home. Nerva is a self-guided app that delivers a gut-directed hypnotherapy program, developed with Dr Simone Peters at Monash University. In a randomised trial of 244 people with IBS in the US and Australia, more people using the app had a meaningful reduction in abdominal pain than those in the comparison group. It suits people who cannot get to a therapist or who would rather start on their own. It is one option among several, and it has not been evaluated by the TGA.

Most people improve substantially with a combination of approaches. The aim is control that lets normal life carry on, which is realistic for most.

What living with IBS is actually like

IBS runs in spells. A flare can last a few days or a few weeks, and it usually follows something identifiable once you look back: a stretch of poor sleep, a period of stress, a run of meals out, a course of antibiotics, a gut infection or, for many women, a particular week of the cycle.

What helps during a flare is dull and effective. Go back to the simpler version of your diet rather than cutting out more and more. Keep eating regularly. Use the medicine that suits your main symptom. Protect sleep, because short nights lower the pain threshold. Keep moving, since regular exercise helps both bowel habit and the pain itself. Then give it time, because flares settle.

A few practical things make a real difference and rarely get mentioned. Know where the toilets are on the route you are taking, because the anxiety of not knowing is itself a trigger. Plan travel and long meetings around the first hours of the day, which are the worst for many people with the diarrhoea-predominant type. Tell your employer only what you want to, but do not suffer a job that gives you no bathroom access.

Come back and be reviewed if the pattern changes or worsens, if you lose weight without trying, if you see blood, if you start waking at night with symptoms, or if what worked stops working. Those are the things that prompt another look rather than another diet.

IBS in women

IBS is more common in women, by about one and a half times in the pooled community data, and women are also more likely to seek help for it. The gap is smaller than is often assumed and is not seen consistently in every part of the world. The reasons are not fully settled and probably include sex differences in pain signalling and in the effect of hormones on the gut.

Many women notice a clear cycle. Symptoms are often worse in the days before and at the start of a period, when hormonal changes affect both gut movement and pain sensitivity. Recognising the pattern is useful in itself, because it makes the bad days predictable rather than random.

Two conditions are worth naming because they are missed for years. Endometriosis frequently causes bowel symptoms and is often labelled IBS first, and pelvic floor dysfunction causes straining and a feeling of incomplete emptying that no laxative fixes. Pain that is strongly tied to periods, pain with sex, or difficulty emptying the bowel despite soft stools should be investigated rather than absorbed into an IBS diagnosis.

In pregnancy, symptoms change in both directions and some of the usual medicines are not suitable, so treatment is planned individually.

Where irritable bowel syndrome is assessed in Sydney

A/Prof Viraj Kariyawasam is a consultant gastroenterologist and hepatologist. Irritable bowel syndrome, and the conditions that have to be separated from it, are assessed at consultation in Norwest, Rouse Hill, Pennant Hills and Macquarie Park.

Where a colonoscopy is needed, it is performed at Norwest Private Hospital, Macquarie University Hospital and Pennant Hills Day Surgery. A referral from your GP is needed for a consultation.