Grandma was wrong: wheat bran and other fibrous foods that do not dissolve easily in water not only fail to soothe irritable bowels, but may actually make things worse, a study reported Friday.
While soluble types of bran, such as psyllium, appear to ease inflamed bowels, the insoluble varieties that have long been a staple for people in search of regularity don't work as advertised, the study found.
Bran is the hard outer layer of grains. Psyllium, also referred to as isphagula, is derived from the seed husks of the Plantago ovata plant, and is the chief ingredient in many over-the-counter laxatives.
In many countries, doctors recommend daily doses of fibre in the form of insoluble bran, but there have been very few rigorous studies to see whether boosting intake of this type of fibre actually works.
A team of researchers from the Netherlands led by Rene Bijkerk of the University Medical Centre set up clinical trials to find out.
They divided 275 patients into three groups, and gave each a different 12-week treatment regimen.
One group ate 10-grams of bran twice a day, and a second ate the same quantities of psyllium, which forms a gel-like substance when mixed with water.
A third group ate a neutral placebo made out of rice flour, which contains no fibre at all.
All but six percent of the participants were Caucasian, and more than three-quarters were women, who suffer from IBS more than men.
The patients had either been diagnosed as having the syndrome within the last two years, or fulfilled other criteria for chronic bowel-related problems.
A standardised scale measuring the severity of symptoms showed that psyllium was the most effective treatment, even after only one month.
After three months, the severity was reduced by 90 points in the psyllium group, 49 points in the placebo group, and 58 points in the bran group.
The slight difference between the bran and the rice gruel placebo was judged statistically insignificant.
"Bran showed no clinically relevant benefits, and many patients seemed not to tolerate bran," the researchers reported in the British Medical Journal.
"Indeed, bran may worsen symptoms of irritable bowel syndrome and should be advised only with caution."
Previous studies have linked soluble fibres to healthy blood cholesterol levels and a better regulation of blood sugar levels.
Food sources that contain soluble fibre include psyllium, barley, oatmeal, lentils, fruit and vegetables.