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The low FODMAPs diet and Irritable Bowel Syndrome

Irritable Bowel Syndrome (IBS) is a functional disorder of the gastrointestinal tract. It affects around 11% of the global population and is more common in women than men. Estimates suggests the prevalence in the UK is around 10-19%. However, it differs greatly between regions and prevalence is 12% in Northern Europe compared to 21% in South America and 7% in South East Asia.

Its causes are poorly understood and therefore it can be difficult to manage. However, it is thought that it may be due to an overly sensitive intestine. Symptoms can be triggered by psychological and social factors, but diet can also worsen the effect.

IBS can reduce quality of life dramatically and patients report symptoms such as; bloating, wind, burping, stomach pain, diarrhoea and constipation (among others). There are 4 subtypes; constipation-dominant, diarrhoea dominant, mixed IBS or un-subtyped. A diet low in FODMAPs (Fermentable, Oligosaccharides, Disaccharides, Monosaccharides and Polyols) has been shown to decrease these symptoms in some patients, and has been shown to be more effective than traditional dietary advice for IBS patients.

FODMAPs are carbohydrates that are poorly absorbed in the small intestine. They can cause more water to enter the bowel than normal. The undigested food can also provide bacteria naturally found in the gut, a source of food which can then cause gas production. This may then cause the bowel to ‘stretch’ which causes the pain and other symptoms seen in IBS patients. A diet low in these can be used to support IBS suffers, with some studies showing 80% of patients seeing an improvement in their symptoms. 

What does the diet involve?

The diet involves restriction of foods containing moderate to high FODMAPs (some are shown in table 1) in the diet for a set period of time (from 6 to 8 weeks), and then re-introducing each one at varying amounts to test tolerance. Only one food should be re-introduced each week. You can be tested for lactose and fructose malabsorption using hydrogen/methane breath testing, as not all sufferers will be intolerant to these. Onions and garlic are major triggers of gastrointestinal symptoms in a many people who suffer with IBS. Therefore, those following the FODMAP diet should initially avoid these completely. Although it is impossible to completely avoid all FODMAPs, choosing foods low in FODMAPs is the most important aspect when following this diet. 


Example Ingredient

Example Food 


Fructans and galacto-oligosaccharides

Pasta, cous cous, bread (all wheat based products), barley and rye based products, onions and garlic



Dairy products: milk, yoghurt, cream, soft cheese



Fruit, fruit juice, honey, table sugar


Sorbitol, mannitol, xylitol, erythritol, lactitol, maltitol, isomalt, and hydrogenated starch hydrolysates

Food additives (commonly found in confectionery)

Table 1. Shows each FODMAP with an example food ingredient and an example of commonly consumed foods with that ingredient 9.

What does the evidence show?

The majority of studies demonstrate that avoiding FODMAPs can provide significant relief to the majority of IBS patients. However, different studies have shown varying degrees of improvement. With some studies demonstrating an improvement in over 70% of patients and others showing improvements in around 50%.

It is vital only remove potential triggers are removed from the diet. Sufficient information and advice from a health professional about a healthy, balanced diet before starting is vital. Identifying lactose or fructose malabsorption can reduce restrictiveness of the diet in the absence of this. Fructose malabsorption has been shown to be present in approximately 40% of IBS sufferers with a higher prevalence in those of Northern European ethnicity. Whilst lactose intolerance exists in 15-100% with a higher prevalence in Hispanic and Black populations.

It is important to recognise that diet is not the only trigger of symptoms in IBS. Stress and emotions also play a significant role in causing gastrointestinal dysfunction. People with this disorder tend to have higher levels of depression and anxiety. Therefore, psychotherapy may also play a role in the treatment. Medication is sometimes required for pain relief, this may include anti-spasmodics, laxatives (for those with constipation dominant IBS), tricyclic antidepressants or anti-diarrheal agents (for those with diarrhoea dominant).


Research suggests that the FODMAP diet is and effective in improving symptoms of IBS in some people. Adherence to the diet is generally good and can be measured using food diaries. It is important to determine if sufferers are fructose or lactose intolerant to reduce the restrictiveness of the diet for those who are not. Advice and guidance from a health professional is paramount to ensure you are eating a varied, balanced diet. 

Nutritionist Resource is not responsible for the articles published by members. The views expressed are those of the member who wrote the article.

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