http://www.smh.com.au/news/Health/B...6415699078.html

Bottom line on high fibre
January 27, 2005

Fibre levels are under scrutiny, writes Nicholas Bakalar.

Despite the barrage of television commercials that insist otherwise, a diet low in fibre is usually not the cause of constipation, and taking fibre supplements is probably not the cure, according to a new study.

In fact, a fibre supplement can make symptoms worse in some patients, particularly the most severely afflicted. A review study published in the January issue of The American Journal of Gastroenterology suggests many other common beliefs about constipation are also little more than durable myths.

In one study, fewer than half of the patients with self-described constipation had any response to added fibre, and studies comparing people with chronic constipation to groups without the condition showed no difference in their dietary fibre intake.

At best, a diet low in fibre may be a contributory factor in a minority of patients, and fibre supplements may help them, the reviewers, led by Dr Stefan Mueller-Lissner, a professor of medicine at Humboldt University in Berlin, found.

Drinking more liquid is often recommended, but studies show it does not work. Although it may seem that adding water to hard stools will soften them, this is not so.

Will increasing exercise help?

The studies say no. Exercise is largely ineffective in preventing constipation. It seems to help in the elderly if it is part of a broader program, but it does not work in young, severely constipated patients.

So what does work?

"I do start with a trial of dietary fibre," Mueller-Lissner says. "Prunes and other fruits may be effective, although bloating can occur as a side-effect."

If those measures do not work, Mueller-Lissner recommends laxatives.

In addition to the fibre additives, there are three other types: stool softeners (Colonlytely and Glycoprep, for example, both available in Australia) , saline laxatives such as milk of magnesia, and stimulant laxatives, including Durolax and Bisalaz, among others.

"I prescribe macrogol [the active ingredient in Colonlytely and Glycoprep, among others]," Mueller-Lissner says.

"If this is ineffective or not tolerated, I switch to bisacodyl [the active ingredient in Durolax and Bisalax] or a related compound."

These drugs are not harmful in normal doses, he says. Some experts believe that stimulant laxatives, which amplify bowel motility, can increase the risk for colorectal cancer, but the evidence is weak.

Chronic constipation is itself associated with an increased risk of the cancer, but no evidence supports a belief that laxatives used in recommended doses increase the risk.

The New York Times