Avoiding Fiber: A Counterintuitive Solution to Constipation?

I’ve posted on this blog about fiber and colon cancer, noting a lack of evidence supporting a protection by fiber on this disease. But what about the effect of fiber on other maladies? What about the condition fiber is supposed to be most effective at treating? Yep, I’m talking about constipation. Here’s a study I came across recently:

Ho KS, Tan CY, Mohd Daud MA, Seow-Choen F. Stopping or reducing dietary fiber intake reduces constipation and its associated symptoms. World J Gastroenterol. 2012 Sep 7;18(33):4593-6.

In this trial, researcher recruited 63 people with constipation. All participants were asked to reduce their fiber intake as low as they could for 6 months. By 6 months 41 subjects were eating almost no fiber, 16 were eating a low fiber diet, and 6 were eating a comparatively high fiber diet. Thus, this was not technically a randomized trial, although the different groups were compared with each other in the style of a controlled trial.

The high fiber group saw no relief of symptoms at all, but they were small in numbers, older, and were clearly poor compliers. Let’s ignore them and look at the low versus almost no fiber groups.


Among those on the low fiber diet, there was a 20 to 30% reduction in the number of people with constipation, anal bleeding, bloating, and abdominal pain. Among the 41 people on the nearly no fiber diets, not a single person had any of these aforementioned symptoms. Everyone who followed this fiber free diet was free from constipation.

This type of study demands further investigation, since it is clearly weak on its own. Still, the results seem incredible. Hopefully future studies will help us determine how legitimate these results are by using a well randomized control group and, ideally, isolating fiber sources (e.g. Soluble and insoluble).