Fiber – Friend or Foe?


Conventional wisdom states that fiber is essential for gut health and is effective for management of constipation, even argued to be necessary for proper bowel habits.

Fiber has been purported to be beneficial, if not necessary, for many aspects of gut health and for the management of many conditions (ref):

  • Constipation
  • Hemorrhoids
  • Irritable Bowel Syndrome
  • Gastroesophageal Reflux Disease (GERD)
  • Diverticulosis/Diverticulitis
  • Peptic ulcer disease
  • Inflammatory Bowel Disease

The evidence for beneficial effects of fiber in these conditions, however, is weak (ref).  In the case of constipation, it’s known that insoluble fiber increases the amount of stool in the intestine and actually slows down the passage of stool.  Also, individuals with chronic constipation have similar fiber intake to those without.

Generally, people who are seeking help for chronic constipation are already consuming a large amount of fiber.  What, then, is the effect of reducing fiber intake on constipation?  A study in 2012 sought to answer this question by eliminating fiber from the diets of individuals complaining of chronic constipation, and the results are striking.


The study design

63 individuals with unexplained constipation were enrolled in this study, all of whom had undergone colonoscopy to rule out any organic cause.  Anyone with a medical explanation for constipation or history of colon surgery was excluded from the study.

Constipation was defined as the need for straining to pass large bulky stools or less than 1 bowel movement per 3 days over a period of at least 3 months.

The patients were then instructed to eliminate all fiber from their diets for 2 weeks, including vegetables, cereals, fruits, and grains.  After 2 weeks, they were then asked to continue with as little dietary fiber as they were comfortable with.


At the 6-month follow-up, 41 of the 63 patients continued on a no-fiber diet, 16 were on a reduced-fiber diet, and 6 were on a high-fiber diet.  Some chose to resume high-fiber diets due to being vegetarians or for religious or personal reasons.

Bowel movement frequency in the 41 patients on a no-fiber diet increased from 1 every 3.75 days to 1 every 1.0 day.  Of the 16 patients on a reduced-fiber diet, 12 were then having daily bowel movements.  For those who continued with high-fiber diets, bowel movement frequency was 1 every 6.83 days.

Associated symptoms were examined at baseline, 1 month, and 6 months, including anal bleeding, bloating, straining, and abdominal pain.  All of the patients who continued on a high-fiber diet reported continued bloating and straining, whereas those who continued on a no-fiber diet had complete resolution of all associated symptoms.

Friend or Foe?

Despite the long-held beliefs that fiber is essential for regular bowel habits, this study presents evidence to the contrary.  Elimination or reduction of fiber from the diet may, in fact, improve constipation.  It’s time to rethink the role of fiber in our diets.

The authors use an analogy of traffic to explain why increasing stool bulk is not effective at treating constipation.  Increasing the number of vehicles on the road is not a logical solution to reducing traffic congestion.  Similarly, in those who suffer constipation, their colons (highways) that are already packed full of feces (vehicles) are not poised to handle an increasing load of feces (more vehicles) caused by fiber intake.

It’s time to rethink how we approach the use of fiber.  Rather than promoting it as the panacea for gastrointestinal complaints, we must acknowledge that it is illogical to expect improved intestinal function by generating larger volumes of stool.

For those who suffer constipation, increasing fiber is likely not going to be beneficial.  Instead, they should consider the unconventional strategy of reducing (or even eliminating) fiber from their diets.

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