The fibre can worsen the symptoms of the Irritable Bowel Syndrome (IBS), researchers found.
However, another form of fibre, soluble fibre, that is fibre that is able to dissolve in water, does seem to ease the condition, which affects up to one in 10 people at some point in their lives.
Doctors often advise that patients increase their fibre intake as well as drink more water and become more active in an attempt to alleviate the symptoms of IBS.
But bran, which is a form of insoluble fibre, should only be used with “caution” according to the authors of the study, published online by the British Medical Journal warn.
The study looked at 275 patients, aged between 18 and 65 years, who all suffered from IBS.
The group were given either 10 grams of bran,10 grams of a soluble fibre called psyllium, or 10 grams of a placebo, in this case rice flour, twice a day for 12 weeks.
The findings show that bran was no better than a placebo at easing symptoms.
However, one in four of the patients treated with the soluble fibre found that their symptoms subsided so much that they reported two full weeks without pain.
In addition, some of those given bran found that their condition deteriorated and dropped out of the study.
Dr René Bijkerk from University Medical Centre Utrecht, in the Netherlands, and colleagues wrote: “Bran showed no clinically relevant benefit, and many patients seemed not to tolerate bran.”
The results support the addition of soluble fibre such as psyllium, but not bran as an effective first treatment approach in the management of irritable bowel syndrome, he added.