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Tricky ten minutes – ‘what diet should I follow for my IBS?’


Functional gut disorders – of which irritable bowel syndrome (IBS) is the best known – affect 10-20% of the population and are a common presentation in primary care. Diagnosis is usually made on the basis of the history – long-standing symptoms including change in bowel habit associated with abdominal pain, in the absence of alarm symptoms. The term IBS is often also used to describe other functional gut disorders, such as functional bloating, functional diarrhoea or functional abdominal pain, and while some argue that this use is incorrect, it is generally accepted within the medical community.

Reviewing the diagnosis

Patients with IBS often seek advice on diet and it’s important to give evidence-based advice. But it’s also an opportunity to review the diagnosis and wider management.

  • Is the original diagnosis of IBS correct? A brief consideration of who made the diagnosis, and how, is useful. It is important that other chronic gastrointestinal diagnoses such as inflammatory bowel disease or coeliac disease have been excluded. Coeliac serology – while the patient is eating gluten – should have been performed and blood tests to look for inflammation (such as FBC and CRP) should have been checked. Where available, faecal calprotectin assessment is a very useful marker of organic diarrhoea.
  • Is the diagnosis still IBS? Infections or the development of new conditions should always be considered. Ask about alarm symptoms such as weight loss and rectal bleeding.
  • Why has the patient presented now? With chronic conditions there is often a trigger for presentation (or re-presentation) and it is important to identify this to address the patient’s concerns. Any suggestion of new pathology should prompt referral to secondary care.

Tackling the question

Diagnosing functional gut disorders is often straightforward, but management can be challenging.

It is important to make a positive diagnosis and to explain this in a way that fits with the patient’s beliefs of what is wrong with them. This is often time consuming, but is worthwhile in terms of successful management and in minimising future visits. Sometimes reassurance is all that is required, but many patients need some form of intervention. A variety of treatments are available for functional gut disorders. Again, choosing one that fits in with the patient’s beliefs is a good predictor of success.

Diet is important in the management of functional gut disorders and given its safety, acceptability, tolerability and success it should be regarded as the first-line intervention in most patients with IBS. Indeed, most identify dietary triggers for their symptoms and will, quite sensibly, have tried cutting out or reducing specific foods – such as wheat and dairy.

NICE has produced a guideline for patients on dietary treatment for IBS, including easy-to-follow advice that is worth considering in all patients. Simple measures such as cutting down on meal size, and decreasing caffeine and alcohol intake can be very helpful. Similarly, avoiding lactose-containing foods can be highly effective in people with lactase deficiency. Go to to download this leaflet.

A recent dietary intervention, the low-FODMAP diet (fermentable oligo-, di, monosaccharides and polyols) is even more effective than NICE guidance in patients with IBS.1,2 This involves decreasing the intake of foods containing high levels of FODMAPs, for example, honey (fructose), wheat and artichokes (fructans) and stone fruit (sorbitol). Unlike many dietary interventions, it is supported by high-quality clinical trials, and response rates of up to 75% are consistently seen. Patients with bloating and diarrhoea respond particularly well to a low-FODMAP diet.

Although the low-FODMAP diet is relatively easy to follow, it is best administered by a dietician experienced in its use, because they will need to tailor it to the patient and develop a plan for reintroduction of excluded foods. This is time consuming, but evidence is emerging that group sessions can be used effectively to train patients in how to follow the diet. More than 100 dieticians in the UK are trained in administering the low-FODMAP diet.3

Patients often also request food allergy testing, but most dietary triggers in IBS are caused by intolerance rather than allergy.

If you suspect the patient has a true allergy, refer to an allergy specialist. Unfortunately, because of the confusion surrounding dietary triggers, a thriving market in over-the-counter testing for food allergies has developed. These tests vary in their validity, and even the best have limited scientific support for their methodology so their results are difficult to interpret.


Dr Peter Irving is a consultant gastroenterologist specialising in inflammatory bowel disease, functional gut disorders and endoscopy at Guy’s and St Thomas’ Hospital, London, and The London Clinic

Dr Peter Irving is involved in an active research programme investigating the low-FODMAP diet. Some of the research is funded by profits made from the low-FODMAP course and from sale of the dietary resources provided to patients by dieticians. 

This article was produced in collaboration with The London Clinic. For more information, go to



1 Staudacher HM, Whelan K, Irving PM and Lomer MC. Comparison of symptom response following advice for a diet low in fermentable carbohydrates (FODMAPs) versus standard dietary advice in patients with irritable bowel syndrome. J Hum Nutr Diet 2011;24:487-95

2 Gibson PR and Shepherd SJ. Evidence-based dietary management of functional gastrointestinal symptoms: The FODMAP approach. J Gastroenterol Hepatol 2010;25:252-8

3 Kings College London. Short courses. The low-FODMAP diet for functional gastrointestinal disorders 2012. Accessed 25 May 2012




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