Fiber – A Double Agent of Constipation?


There are people who believe fiber is not an important part of a healthy diet. I’m not one of those people. To me, it makes complete sense that the fibers in our diet not only help bulk our poop but also help feed and diversify the bacteria that live in our guts that are proving to be essential to every aspect of human health.


Nevertheless, as a scientist, I always think it’s a good exercise to play devil’s advocate against your own presuppositions and to seriously entertain contradictory data. That’s why I found the paper, “Stopping or reducing dietary fiber intake reduces constipation and its associated symptoms”, published in the World Journal of Gastroenterology by Kok-Sun Ho and colleagues, so fascinating. This paper is genuinely one of the most well-conducted studies I’ve read examining the relationship between fiber as constipation. It showed that reducing fiber improved the constipation, and related symptoms, in participants.


In this study, 63 patients with constipation were asked to go on a no fiber diet for two weeks, followed by following a normal fiber, reduced fiber, or no fiber diet for 6 months. The results were striking! Of those who went on the no fiber diet, poop frequency increased from one poop every 4 days to one poop per day! Those who reduced fiber also saw a roughly two-fold improvement in poop frequency, pooping every other day; and those who ate the high-fiber control diet saw no improvement in constipation.


Related symptoms, like bloating and straining, also improved remarkably in the no fiber and, to a lesser extent, the low fiber groups.


These data don’t equate to proof that reducing fiber will improve constipation. Personally, I’m still sceptical. They are, however, sufficiently robust to challenge the dogma that fiber is universally good for constipation. I quite like the authors’ analogy: “The role of fiber in constipation [can be] analogous to cars in traffic congestion… Should we add more cars, the congestion [could be] worsened.”



In the end, all that matters is what works for you and your poo!

Nicholas Norwitz

*The views and opinions expressed herein are those of the author and do not necessarily reflect the views of, its affiliates, or its employees.