Last chance in 2024 to join PN Coaching + save up to 54%

  • Become the healthiest, fittest, most confident version of you
  • Lose weight, gain lean muscle, and feel more energy
  • Transform your body and your health in 2024

Research Review: Can lowering fiber intake help with constipation?


If you suffer from constipation, you’ve probably been told to increase dietary fiber. But a recent study suggests that eliminating fiber might be a better way to reduce the symptoms of chronic constipation. Is this a better choice?

In this week’s Research Review, we’ll explore some findings that go directly against what we’re commonly told when treating constipation, and leave you with… ehem, the bottom line.

What goes in must come out

Caca, turd, doo-doo, or poop. However much we joke about the product of elimination, most people probably don’t give the process a whole lot of thought.

But bowel function is actually quite complex, involving the coordination of a number of nerves and muscles. Here’s how it works:

The bowel is part of the digestive or gastrointestinal (GI) tract, which is designed to absorb nutrients from whatever we eat and drink. Nutrients like proteins, fats, carbohydrates and vitamins are absorbed in the small intestine.

Anything the body can’t use continues to the large intestine, also known as the colon. Here, water is reabsorbed, along with some minerals, and then the remaining foodstuff is formed into stool.

Now, if you have a sensitive stomach, prepare yourself for this next bit.

There’s some variation in “normal” stool. But, in general, it will be smelly (because of bacterial fermentation), it should be brown (due to the bile), and it should be a soft consistency, like toothpaste. In other words, you shouldn’t have to bug out your eyeballs trying to pass it (1).

How often should you poop?

Frequency varies. There’s no “normal” number of times a person should go, but rather averages.

Some people poop every day at the same time, like clockwork. Others go a couple of times a day. Still others go every other day, or maybe once or twice a week. (Factoid! Sloths poop only once a week, and they must climb down to squat at the base of a tree to do it.)

This variation makes it difficult to define “constipation”. Our bowel speed can vary depending on our individual makeup, our age and sex, what we’ve eaten, our lifestyle, stress, etc.

However, if:

  • you pass fewer than three stools per week;
  • they are hard and dry (2, 3); and
  • bathroom time can be a bit of a challenge…

…then you are probably constipated.

Common treatments for constipation

Most constipation is temporary. Maybe you’ve changed your diet recently or undergone some stress. Ordinarily, your bowels will return to normal soon after your life returns to normal.

But what happens if constipation becomes chronic?

The most common recommendations are to eat more fiber, drink more water, and get more exercise (1, 2, 3).

What if these tricks don’t get things moving? Well, most people move on to stool softeners, schedule a visit to their MD – or even resort to colonic irrigation. Yup, that is definitely one way to keep your colon clear!

Speaking of colonics, these were the focus of the movie The Road to Wellville staring Anthony Hopkins and Matthew Broderick. Who would have guessed that John Harvey Kellogg, a holistic medical doctor and the inventor of corn flakes, was also a proponent of vegetarianism and colonics?

Not all constipation is created equal

Truth is, most common treatments for constipation lack scientific support. And they’re often chosen without much forethought.

Before we decide on treatment, we should know what type of constipation we’re dealing with.

Constipation due to slow transit time may respond well to pharmacological agents like stool softeners, or may improve if the patient increases water, exercise, or fiber – assuming s/he is deficient in one or all of these.

Common bulk forming agents like psyllium and bran can help in these situations. There is some evidence that Traditional Chinese Medicine and probiotics can also be useful. (See Research Review: Good bacteria, gut health and exercise.)

However, in cases where the cause of constipation is idiopathic (arising spontaneously from an unknown or obscure cause) evidence-based options for treatment are pretty much lacking (3, 4).


Research question

This week’s review investigated whether changing the amount of fiber in the diets of people with idiopathic constipation would have any effect. Specifically, the researchers wanted to learn if less dietary fiber (rather than more) might relieve the participants’ symptoms and help them poop.

Ho, Kok-Sun, Tan, Charmaine You Mei, Daud, Muhd Ashik Mohd, Seow-Choen, Francis. (2012, Sept). Stopping or reducing dietary fiber intake reduces constipation and its associated symptoms. World J Gastroenterol. 18(33):4593-4596. doi: 10.3748/wjg.v18.i33.4593


This study was a prospective longitudinal case study in which the individual participants served as their own control. Researchers use this type of design when they want to focus on how individuals respond to an intervention over the course of an extended time period, versus how groups respond.

While we can draw correlations from studies designed like this, we cannot establish cause and effect.


The subjects had all sought clinical help for symptoms of constipation, abdominal distention, pain or bloating, and difficulty in passing stools with or without symptoms of rectal bleeding.

The researchers defined constipation as passing stool less than once every three days for a period of at least three months, or having trouble with bowel movements.

They didn’t do a whole lot more to classify the kinds of problems these people were having, but they did perform colonoscopies to make certain that colonic lesions weren’t contributing to their difficulties.

63 participants who suffered from constipation were tracked for six months – 16 males (25.6%) and 47 females (74.4%), with a median age of 47 years (range 20-80 years).

At the start of the study, researchers noted that all the subjects were on high fiber diets or taking fiber supplements.

Experimental protocol

The researchers explained to participants how the gastrointestinal tract works and described the bulking effect of dietary fiber.

  • For the first two weeks, participants eliminated all fibrous vegetables, fruits, whole grain bread, cereals, and brown rice. They could eat clear vegetable soup and sieved fruit juices, but not much more in the carb department, leaving them with a pretty limited selection of food choices.

I’m envisioning an all-protein diet and a lot of refined carbs. Vegetarian participants had to trade all their whole grains for processed white grains, and even their beans for processed bean products! That must have meant dried, powdered beans like those mixes you can buy to make hummus.

All in all, it sounds pretty unhealthy to me, but hey, the protocol supported the research question.

  • During the initial two-week no-fiber period, participants were asked not to take laxatives.
  • After the two-week no-fiber diet period, participants continued on a low fiber diet for a total of six months. They came for follow up at the end of month one and in month six, and final results were analyzed at six months.


The researchers collected both objective and subjective data.

Objective data included: age, sex, and symptoms of constipation (recorded as the interval in days between bowel movements).

Subjective data included the participants’ measure of difficulty in taking a poop (of course, the researchers called this “evacuation.”)

Participants ranked the difficulty on a scale that went from: “no straining” to “moderate straining” to “straining most of the time.”

Researchers collected information about general dietary fiber intake, but the paper did not discuss how they did so (via a diet log, etc.) or what they classified as a “no fiber,” “low fiber,” and “high fiber” diet.

I e-mailed the lead researcher but didn’t receive a response. I’d like to know this information in order to place the results in context, but more on that later when I discuss the study’s strengths and limitations.


The researchers wanted to explore whether common beliefs about the use of fiber in reducing constipation are valid. Specifically, they wanted to learn whether decreasing fiber intake could help patients with idiopathic constipation.

What they found was that in this study population, subjects who followed a low fiber diet for 6 months did experience more frequent bowel movements.

  • 6 months: 63 participants initially enrolled and 61 completed the study. Of those, 41 participants continued on a no fiber diet, 16 on a low fiber diet, and 6 returned to a high fiber diet.
Symptom Symptoms at study initiation (n=63) High fiber diet (n=6) Reduced Fiber Diet (n=16) No Dietary Fiber (n=41)
Anal bleeding 31 4 4 0
Constipation 63 6 12 0
Bloating 33 6 5 0
Strain in bowel 63 6 9 0
Abdominal pain 13 3 2 0

After 6 months, the 41 participants who stopped their fiber intake went from having a bowel movement once every 3-4 days on average to one BM per day.

Of the 16 who followed a low fiber diet, 12 had a bowel movement every day, 3 had one every 2-3 days, and 1 had a movement every 4-6 days.

The 6 participants who stayed on a high fiber diet had no change in the frequency of their bowel movements, with one every 6-7 days.

The results of decreasing fiber intake were statistically significant, not only in terms of increasing the frequency of bowel movements, but also in decreasing the other symptoms associated with constipation such as bloating and straining.


Surprised by the results? I know I was, as these findings go directly against what we commonly hear about treating constipation.

The study results do show a strong correlation between decreasing dietary fiber intake and improving symptoms of constipation.

But why?

First, the researchers speculate that there may be a disconnect between what the layman classifies as constipation and how it should be treated, and what constipation actually is.

Most people define constipation as failing to pass stool. And what we’re told is that if we make more poop (by adding more fiber to the diet and bulking things up), it will be easier to “go.”

However, here, the researchers speculate that the role of fiber in constipation is like merging cars in a heavy traffic.

If there’s a jam, adding more cars doesn’t clear up the congestion. So why would adding more fiber and increasing the volume and bulk of poop make it easier to go?

This analogy sounds plausible. At the same time, I don’t think we can draw any broad conclusions from a single study.

More information about the amount and type of fiber in participants’ diets and their other habits such as activity levels would have been useful here. Plus, the sample size was too small to allow us to safely generalize.

Also, we should keep in mind that there are different causes for constipation, and different causes may demand different treatments. In fact, a recent review of the existing literature concluded exactly that (3).

Here, the reviewers noted that patients complaining of constipation require a full medical workup to determine the reason for the problem. If the cause of constipation is not enough fiber, fluids, or exercise, the traditional triage of treatments should help.

If the cause is slow transit time, then pharmacological and bulking agents like psyllium are probably a better bet.

If constipation is caused by a pelvic floor disorder, then there is some evidence to support biofeedback as a treatment. Meanwhile, Traditional Chinese Medicine might also be of value in certain cases.

With regards to the study we’ve been reviewing, the cause of constipation was idiopathic and the subjects were already on a high-fiber diet. That is probably why increasing fiber wasn’t such a great idea in this case. 

But again, generalizing from this particular case would be a mistake.

In reality, there aren’t many studies examining the common treatments for constipation such as lifestyle changes, biofeedback and pharmacological agents. More research in this area would be helpful (3).

Bottom line

Not all constipation is created equal, so when considering treatments, it’s important to determine the cause.

First, consider whether your bowel movements are less frequent than is normal for you. You are your own best standard.

Then, assess your current fiber intake, level of exercise and fluid intake.

Current fiber recommendations suggest adults should consume around 20-35 grams of fiber per day or about 11 grams per 1000 calories.

For exercise you should aim to be active in some way most days for at least 30 minutes (for chronic disease prevention) and 60 minutes (for weight management).

Meanwhile, you should drink around 3-4 liters per day if you’re a man, and 2-3 liters per day if you’re a woman (5, 6).

If you are hitting the mark for all of these, you should probably visit your doctor to determine the root cause of your problem, and the appropriate method of treatment.

But I wouldn’t recommend staying on a low-fiber diet without medical supervision, because at this time, the long-term effects are unknown.


Click here to view the information sources referenced in this article.

Learn more

Want to get in the best shape of your life, and stay that way for good? Check out the following 5-day body transformation courses.

The best part? They're totally free.

To check out the free courses, just click one of the links below.