Update on constipation: One treatment does not fit all
ABSTRACTConstipation is a common clinical problem that can be difficult to manage. It has a variety of identifiable causes, but even idiopathic constipation has different possible mechanisms. Often, the key to improvement and patient satisfaction is to understand the mechanism and the patient.
KEY POINTS
- A high-fiber diet often improves functional constipation, but it may worsen slow-transit constipation or dyssynergia (a failure of the pelvic floor muscles to relax). Nevertheless, fiber remains a mainstay of treatment for its ability to provide homogeneous stool consistency.
- Drugs approved for treating constipation increase fluid in the lumen, speed intestinal transit, and improve stool consistency, while tegaserod (Zelnorm) additionally acts as a serotonin agonist.
- Colonoscopy and other tests are reserved for patients with refractory constipation and those with symptoms suggesting colon cancer.
- Prebiotics (short-chain carbohydrates that stimulate activity of beneficial colonic bacterial flora) and probiotics (live bacterial preparations) are under evaluation as treatments for chronic constipation.
BULK LAXATIVES (FIBER SUPPLEMENTS): THE FIRST-LINE TREATMENT
Fiber remains the first-line treatment for constipation. It may relieve or improve symptoms in functional constipation. However, fewer than 30% of patients with either slow-transit constipation or pelvic floor dysfunction have improvement in symptoms with fiber, and in these types of constipation it can even worsen symptoms.40
There is much confusion about what types of fiber should be recommended and how the various types of fiber perform in resolving constipation.
Insoluble fiber
Insoluble fiber resists bacterial degradation in the colon and can retain more water than soluble fiber can.
Bran 20 g/day increased the frequency of bowel movements by 55%, increased fecal weight by 157%, and decreased intestinal transit time by 50% in women who had three or fewer bowel movements per week.41
Muller-Lissner42 and others performed a meta-analysis and found that bran (25 g/day) increased stool weight and decreased transit time in both healthy controls and patients with chronic constipation. Yet constipated patients taking bran still had lower stool weights and slower transit times than did healthy subjects.
When bran 20 g/day was compared with placebo in chronically constipated patients, bowel frequency and stool weight increased with both treatments,43 suggesting that factors other than intake may affect bowel function and transit time. However, bran was more effective than placebo in decreasing oroanal transit time.
Elderly constipated patients who received bran 10 g twice a day had significantly shorter transit times (89 hours vs 126 hours) than did those who received psyllium (a soluble fiber) 6 g twice daily. They also needed less additional laxative.44
Soluble fiber
Soluble fiber also affects the bowel habits of both healthy and constipated patients.
Methylcellulose, given to healthy volunteers at a dose of 4 g/day, resulted in statistically significant increases in stool weight, fecal water weight, and fecal solids.45 In constipated patients, methylcellulose 1 g/day was as effective as psyllium 3.4 g/day at increasing stool frequency, fecal water weight, and fecal solids.45
Konjac glucomannan was also shown to significantly increase stool frequency, water weight, and fecal solids.46
Psyllium. In a study that randomly assigned 22 patients with chronic constipation to receive either psyllium 5 g twice daily or placebo for 8 weeks, followed by a 4-week washout phase in which placebo was given,47 those who received psyllium reported significant improvements in stool consistency and pain with defecation, as well as significant increases in both stool frequency (3.8 vs 2.9 per week, P < .05) and stool weight (665 g vs 405 g, P < .05). However, colonic transit times and anorectal manometric measurements did not differ significantly between those who received psyllium vs placebo.47
Fiber may not help everyone
Others have also shown that while fiber may improve stool characteristics, it may not significantly alter the sensorimotor functions of the colon and pelvic floor.
Cheskin et al48 performed a crossover study in 10 constipated men and women in the community. Patients received either 24 g of psyllium fiber daily or a placebo fiber for 1 month and then crossed over to the other treatment for the next month. The most common cause of constipation in this study was pelvic floor dysfunction. Total gut transit time was significantly increased by psyllium fiber, and there was a trend toward increased stool frequency, demonstrating that psyllium clinically improved constipation. However, pelvic floor dysfunction, as measured by rectal manometry, was not improved.
It may be that only people with normal-transit constipation, not those with underlying slow-transit constipation or pelvic floor dysfunction, are helped by additional dietary fiber. Voderholzer and others40 studied 149 consecutive patients with chronic constipation and evaluated their response to at least 6 weeks of psyllium (Plantago ovata seeds 15 to 30 g/day) by serial symptom measurements, oroanal transit times, and functional rectoanal evaluation with defecography, manometry, and sigmoidoscopy. Of the patients with no evidence of pelvic floor dysfunction or slow-transit constipation, 85% improved. However, 80% of those with slow-transit constipation and 63% of those with pelvic floor dysfunction did not improve with the use of fiber. The authors concluded that it is reasonable to try dietary fiber in patients with constipation and, if no improvement is noted, to then consider further investigation for other subtypes of constipation (ie, slow-transit or pelvic-floor dysfunction).
Adverse effects may limit the use of fiber and may differ depending on the type of fiber used. Soluble fiber may be better tolerated, especially in patients with constipation-predominant irritable bowel syndrome.49 Side effects include the sensation of bloating and distention, excessive gas production, and abdominal cramping.
Our recommendations on fiber
We recommend the following regarding fiber in constipated patients:
- Increase fiber intake from natural foods up to 20 g/day. This increase should be completed over 2 to 3 weeks to minimize adverse effects.
- Consider adding a fiber supplement, such as psyllium, if increasing the intake of natural fiber does not relieve constipation-related symptoms.
- If symptoms persist despite the use of fiber supplements and diet and lifestyle modification, then further structural and functional investigation of the colon (anorectal manometry, colonoscopy, defecography, colon manometry) should be considered.
