Irritable bowel syndrome is a common condition
A soluble fibre supplement should be the first line of attack in treating irritable bowel syndrome, experts say.
Researchers from Utrecht University in the Netherlands compared adding bran, a soluble supplement called psyllium and a dummy supplement to sufferers' diets.
They found psyllium was the most effective, warning that bran may even worsen the symptoms of the condition, the British Medical Journal reported.
As many as one in 10 people is estimated to have the condition.
It is characterised by abdominal pain and an irregular bowel habit.
Its exact cause is unknown and recommendations for treatment include dietary advice, antidepressants and drug treatments.
Many relying on dietary adjustments still turn to bran in a bid to help improve the way the intestines work.
But the Dutch study of 275 patients questions the wisdom of this approach.
The team gave patients 10g of either psyllium, bran or rice flour twice a day for 12 weeks.
At the end of the study, those on psyllium, a naturally occurring vegetable fibre, reported symptom severity had been reduced by 90 points using a standard scale of rating problems.
For bran it was 58 points and for the placebo group, 49.
The report also showed that patients seemed less tolerant of bran, with more than half of the group dropping out during the trial, mostly because their symptoms worsened.
Soluble fibre can also be found in fruit such as apples and strawberries, as well as barley and oats.
But Dr Niek de Wit, one of the researchers, said: "It is unlikely that people with IBS would get enough from fruit and other foods to help them.
"I think adding psyllium to the diet is the best treatment option to start with. In the study, people did this by adding it to things such as yoghurt and it had a real effect."
Dr Anton Emmanuel, medical director of Core, the charity for diseases of the gut, said bran was being over-used.
He said the study was "helpful" and "reasonably robust", adding: "Putting it all together, patients should tolerate this form of fibre well and it may help some, especially those with a tendency to constipation."