Very little evidence for cutting out certain carbs to ease irritable bowel

There is very little evidence to recommend avoiding certain types of dietary carbohydrate, known as the FODMAP diet, to ease the symptoms of irritable bowel syndrome, or IBS for short, concludes a review of the available data in Drug and Therapeutics Bulletin (DTB).

IBS is characterised by abdominal pain/discomfort and altered bowel frequency in the absence of any obvious gut abnormalities. Symptoms can include abdominal bloating, which eating can worsen.

Up to one in five of the population is thought to be affected, with women twice as likely to develop IBS symptoms as men.

Treatment options include dietary and lifestyle advice, psychotherapy, and drugs to curb painful spasms and associated diarrhoea and/or constipation.

Dietary advice usually includes the recommendation to reduce intake of insoluble fibre, limit fresh fruit to three portions a day, take regular meals, avoid rushing food or eating on the go, and to steer clear of the artificial sweetener sorbitol.

The low FODMAP diet, which was developed in Australia, is based on the observation that certain types of short chain carbs are poorly absorbed by the small intestine and that IBS symptoms worsen when these are eaten.

These short chain carbs are present in wheat, onions, and legumes; milk; honey, apples, and high fructose corn syrup; and the artificial sweeteners used in confectionery (sorbitol and mannitol). They are rapidly fermented in the gut, increasing water volume and gases.

After assessing the available published evidence and the three UK guidelines on the management of IBS, DTB says that all the trials provide some evidence that patients feel the diet reduces some of the symptoms.

And one study indicates that the diet changes the profile of the bacteria in the gut, although what the clinical implications of this are, or, indeed, what the long term effects might be, are unclear, says DTB.

But data to back the use of a low FODMAP diet as an effective treatment to control symptoms "is based on a few relatively small, short term unblinded or single blinded controlled trials of varying duration," it cautions.

And dietary manipulation is not without its drawbacks as some people fail to maintain a balanced diet when trying dietary exclusions, says DTB.

While some guidelines suggest that a low FODMAP diet might be appropriate for motivated patients for whom other treatments have failed to relieve symptoms, this should only be done under the supervision of a dietitian with specialist expertise in this type of dietary intervention, it recommends.

And it concludes: "However, we believe that patients should be advised that there is very limited evidence for its use, the ideal duration of treatment has not been assessed in a clinical trial, and its place in the management of IBS has not been fully established."