Research & Education

Could Increased Fiber Worsen Constipation?

It can be frustrating for healthcare professionals when patients swear they’re doing “all the right things,” but the condition in question isn’t improving. Of course, it’s equally frustrating—if not more so—for the patients, who are following doctors’ orders and doing everything they’re supposed to, yet are not experiencing the expected results. This situation happens all too frequently for those who experience chronic constipation: they pursue the traditional remedies, yet things “don’t come out” as promised (if you’ll pardon the pun). And if you’ve ever dealt with chronic constipation, yourself, then you know you really, really want this remedied, and fast.

People tend to get a bit…tight…when they haven’t had a bowel movement in a few days. (Pardon the pun, again.) But constipation isn’t defined by having a BM daily. According to the American Society of Colon & Rectal Surgeons, “The belief that one must have a bowel movement every day simply is not accurate and can lead to unnecessary concern and even abuse of laxatives.  In fact, if one’s daily bowel movement is hard, requires great effort to expel, or does not satisfactorily empty, the individual would still be considered to have constipation in spite of having a ‘normal frequency.’  On the other hand, if one has a movement every third day but it is not hard, does not require straining and completely evacuates, then one may very well consider this normal bowel movement, in spite of the fact it is not a daily event.”

So people shouldn’t worry if they go a couple of days without a BM, but if it’s been a while, or if someone does go regularly, but there’s pain and straining involved, then constipation is a factor. And the longer the stool remains in the colon, the more water will be reabsorbed, resulting in stools that are harder and drier, making the problem even worse. Add to that the possibility that waste products might also be reabsorbed into the body, and chronic constipation is just all around bad news.

Conventional go-to advice for chronic constipation includes increased water and fiber intake, and increased physical activity. And while these may work for some people, what happens when someone already gets enough water and fiber? What if they already exercise? More of the same isn’t guaranteed to help. In fact, researchers note, “these measures are effective in only a subset of patients. Clinical trial data supporting the effectiveness of such approaches are limited and, in general, do not support their benefit in providing relief of symptoms, particularly when evaluated in patients with chronic constipation.”

Increasing water intake might be beneficial for the subset of patients who have clear signs of dehydration, but if inadequate fluid intake isn’t the problem, then more fluids probably isn’t the answer: “There is no evidence that constipation can successfully be treated by increasing fluid intake unless there is evidence of dehydration.”

The same could be said for increasing dietary fiber. Increased fiber intake might help the subset of patients whose constipation is caused by inadequate fiber. But this is only a subset. According to researchers, “A diet poor in fiber should not be assumed to be the cause of chronic constipation. Some patients may be helped by a fiber-rich diet but many patients with more severe constipation get worse symptoms when increasing dietary fiber intake.”

Increased fiber is an especially interesting recommendation. For a substantial number of patients, constipation is caused by impaired intestinal motility. In these individuals, more fiber would be more likely to make constipation worse, not better. If colonic motility is compromised, and stool is already not passing through in a reasonable amount of time, then increased dietary fiber is going to result in larger, bulkier stools that are still not being passed through. So ultimately, this frequently cited recommendation sounds good in theory, but could very well end up exacerbating the problem. Researchers have observed as much: “For many patients, fiber exacerbates bloating and distension, leading to poor compliance.” Imagine being a patient with chronic constipation: your doctor suggests consuming more fiber. You do so, and you feel even worse.

Several health conditions are known to contribute to secondary constipation, including hypothyroidism, Parkinson’s disease, and hyperparathyroidism. Several commonly prescribed medications can also interfere with intestinal motility or other factors leading to constipation, such as NSAIDs, anticonvulsants, antidepressants, calcium channel blockers, and aluminum-containing antacids. Hypercalcemia and hypokalemia may also result in constipation. Under these circumstances—constipation induced by factors other than a lack of dietary fiber—more fiber probably isn’t going to help.

With this in mind—that reduced intestinal motility, whatever the cause—would be a contraindication for increased dietary fiber, let’s look at a fascinating study in which the authors concluded, “Idiopathic constipation and its associated symptoms can be effectively reduced by stopping or even lowering the intake of dietary fiber.” Talk about going against conventional wisdom!

The study involved 63 adults (16 male, 47 female; median age 47, range 20-80 years old) with idiopathic chronic constipation. Colonoscopy had ruled out an organic cause for the condition, and patients with previous colon surgery or a medical cause for their constipation were excluded. They were instructed to follow a no fiber diet for two weeks. After that, they were asked to reduce their dietary fiber intake “to a level that they found acceptable.” Dietary fiber intake, symptoms of constipation, difficulty in evacuation of stools, anal bleeding, abdominal bloating or abdominal pain were recorded at 1 and 6 months. The findings say it all:

At 6 months, 41 patients remained on a no fiber diet, 16 on a reduced fiber diet, and 6 had resumed a high fiber diet for religious or personal reasons. “Patients who stopped or reduced dietary fiber had significant improvement in their symptoms while those who continued on a high fiber diet had no change. Of those who stopped fiber completely, the bowel frequency increased from one motion in 3.75 d (± 1.59 d) to one motion in 1.0 d (± 0.0 d) (P < 0.001); those with reduced fiber intake had increased bowel frequency from a mean of one motion per 4.19 d (± 2.09 d) to one motion per 1.9 d (± 1.21 d) on a reduced fiber diet (P < 0.001); those who remained on a high fiber diet continued to have a mean of one motion per 6.83 d (± 1.03 d) before and after consultation. For no fiber, reduced fiber and high fiber groups, respectively, symptoms of bloating were present in 0%, 31.3% and 100% (P < 0.001) and straining to pass stools occurred in 0%, 43.8% and 100% (P < 0.001).

That’s right: the group on a no fiber diet had the most frequent bowel movements, and also experienced complete resolution of bloating and straining.

This flies in the face of “conventional wisdom,” but we’ve seen conventional wisdom crumble in several other areas over the last few years: saturated fat isn’t bad for you, amyloid proteins don’t cause Alzheimer’s, statin drugs may actually cause cardiovascular problems. So why not fiber for relieving constipation? It’s possible this is another long-held belief that has outlived its expiration date.