How can the Low FODMAP diet help people with IBS?

The Low FODMAP diet is rapidly becoming a standard diet therapy for people with irritable bowel syndrome (IBS) and the success of the diet in reducing symptoms for the majority of people has improved the lives of many people living with IBS. IBS is a functional chronic condition; in other words a disorder of the way the bowel works or moves, producing symptoms of diarrhoea, constipation or alternating between both, plus abdominal pain and bloating.

The cause of IBS is unknown, but it is suspected to involve gut microbes, a hypersensitive bowel and nerve signalling between the bowel and brain - some people develop IBS after a bout of gastroenteritis, which can involve very low levels of bowel inflammation.

What are FODMAPs?

For many years people with IBS have reported symptoms with food and the development of the Low FODMAP diet in Australia in 2008 verified what patients have always known - eating certain foods increases symptoms of IBS. These foods are known as FODMAPs, non-digestible sugars that draw fluid into the bowel before being fermented by large bowel microbes.

The acronym FODMAP stands for Fermentable Oligosaccharides (fructans, fructo-oligosaccharides and galacto-oligosaccharides), Disaccharides (lactose), Monosaccharides (fructose) and P olyols (sorbitol, mannitol and xylitol). The process of drawing fluid into the bowel and the fermentation of FODMAPs by bacteria produce wind, which increases pain and bloating in an IBS sensitive bowel. Symptom improvement follows reduction of high FODMAP foods, including improvement in bowel habit, especially diarrhoea. These sugars are found in a wide variety of foods in the diet and not everyone with IBS will have symptoms with all of them.

How does the FODMAP diet work?

The diet involves reducing high FODMAP foods for eight weeks and then re-introducing them, using a specific protocol, to identify which ones are problematic for the individual person. Patients then follow a FODMAP modified diet, individual to their own circumstances. Re-introduction of high FODMAP foods to identify symptom triggers is very important, because we do know that a FODMAP diet results in changes in numbers of good bacteria found in the bowel. This is because some FODMAPs are also prebiotic, food for gut bacteria. Having varied good bacteria populations in our large bowel is important for long-term bowel health. We do not know the long-term effects of a complete FODMAP restricted diet, so increasing consumption of prebiotic-containing foods that are tolerated well, is necessary.

Don't go it alone - or self-diagnose

The diet should be completed with the help of a FODMAP knowledgeable dietitian, to ensure that the nutritional content of the diet is not compromised; advice is provided that is up-to-date and the person is fully informed about suitable foods to eat, to facilitate ease of dietary change. With advice in mind, note that most FODMAP food lists available online are out of date or incorrect. It is also important not to self-diagnose - see your GP if you are experiencing digestive symptoms suggestive of IBS. A GP or gastroenterologist can refer patients with IBS to a dietitian to follow the FODMAP diet when simple lifestyle changes have been attempted and symptoms persist.

Julie Thompson is a Health and Care Professions Council registered Clinical Lead Dietitian working in the NHS and private practice. She is an executive on the board of The IBS Network and regularly writes posts for the blog


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