Older "overlooked" treatments for irritable bowel syndrome may end up being the best option for patients, research suggests.

Fibre, and peppermint oil were found to be effective in a review of the evidence.

Guidelines on IBS should be updated in light of the findings, the researchers say in the British Medical Journal.

A UK expert said there had been a general feeling among doctors that the therapies "didn't work".

Between 5% and 20% of the population is estimated to suffer from IBS which is characterised by abdominal pain and an irregular bowel habit.

The exact cause of the condition is unknown and recommendations for treatment include dietary advice, antidepressants and alternative therapies.

Fibre, and peppermint oil are used to treat IBS, but evidence of their effectiveness is unclear because of conflicting results from studies, the researchers said.

They have also been overlooked because of the focus on newer more expensive drugs which ended up being withdrawn due to lack of efficacy and safety concerns, they added.

Benefits

By trawling through all the studies comparing the therapies with dummy pills or no treatment, the researchers were able to look at data from 2,500 adult patients with IBS.

Fibre, and peppermint oil were all found to be effective, with doctors needing to treat 11, 5 and 2.5 patients, respectively for one patient to benefit.

Insoluble fibre such as bran was not beneficial; only isphaghula husk - a soluble form of fibre - significantly reduced symptoms.

Hyoscine - extracted from the cork wood tree - was the most successful and should be the first choice, the researchers said.

Out of all three treatments, peppermint oil seemed to come out on top.

Study leader Dr Alex Jones, a gastroenterologist who has recently moved from Canada - where he did the research to St James University Hospital in Leeds - said the treatments were cheap, safe and had been in use for 15 to 20 years.

"They fell out of favour with the development of new drugs.

"This is good news for patients."

Professor Roger Jones, head of the Department of General Practice at Kings College London, and founding president of the Primary Care Society for Gastroenterology, said: "There is a general feeling that they don't work very well.

"With all of the treatments for IBS, there is a huge placebo effect so it is easy to imagine your treatment is working then the trials come along and suggest they don't.

"This puts these simple remedies back on the agenda."

He added that the study did not pick out which patients would benefit from which treatment but as they are safe and cheap, patients can test what works best for them.