Effectiveness Not Established

Konjac Glucomannan

for Constipation

Konjac glucomannan is produced from the root of the konjac plant, which is native to tropical areas in Asia. It is high in soluble fiber. This dietary supplement has been studied in patients with cancer for the prevention and management of constipation.

Research Evidence Summaries

Chen, H.L., Cheng, H.C., Wu, W.T., Liu, Y.J., & Liu, S.Y. (2008). Supplementation of konjac glucomannan into a low-fiber Chinese diet promoted bowel movement and improved colonic ecology in constipated adults: A placebo-controlled, diet-controlled trial. Journal of the American College of Nutrition, 27, 102–108.

Study Purpose

To examine the effects of konjac glucomannan (KGM) supplementation on bowel habits and colonic environment in adults with constipation, and to examine the method by which KGM modulates bowel habits.

Intervention Characteristics/Basic Study Process

Patients who self-reported having constipation for more than six months were recruited from an outpatient clinic. The study comprised a three-week placebo (gelatin capsules containing corn starch) period, a one-week adaptation period in which KGM was gradually increased from 1.5 to 3 g per day, and a three-week KGM period (1.5 g KGM per meal or 4.5 g per day). Capsules were taken with 150 ml of water. Patients followed a typical low-fiber Chinese diet and were instructed to maintain their usual physical activity, lifestyle, and sleeping habits. Capsule consumption (compliance) was verified daily.

Sample Characteristics

  • The study reported on a sample of seven women.
  • Mean patient age was 45.9 years (SD = 2.7).
  • Patients self-reported having constipation (less than one bowel movement per day or straining with bowel movements).
  • None of the patients used laxatives or enemas.



Study Design

This was a single-blind, placebo-controlled, crossover study.

Measurement Instruments/Methods

  • Patients recorded the following on a daily basis: ease of bowel movements, symptoms (e.g., feeling of incomplete evacuation, abdominal cramping, borborygmi, bloating, flatulence), and stool consistency.
  • Participants collected their stools on days 15 through 21 during the placebo- and KGM-periods to determine fecal weight, composition, microflora, pH, and short-chain fatty acid content.


  • Frequency of defecation and feelings of relief after bowel movements significantly improved (p < 0.05) by the second and third weeks of KGM.
  • Ease of passage of bowel movements and reduction in the severity of borborygmi significantly improved (p < 0.05) by the third week of KGM.
  • Flatulence significantly increased (p < 0.05).
  • KGM did not significantly decrease abdominal cramping or bloating or significantly soften feces.
  • KGM significantly increased proportions (percentage of total bacteria) of bifidobacteria and lactobacilli, and decreased the relative proportion of clostridia, compared with placebo (p < 0.05).


Adding KGM (4.5 g per day) to a low-fiber diet may increase frequency of bowel movements and improve colonic ecology.


  • The sample size was extremely small.
  • Participants were all women and volunteers.
  • Patients with cancer were not included. 
  • The design was only single blinded.

Nursing Implications

KGM (4.5 g per day) may increase frequency of bowel movements in adults with mild constipation (participants did not use laxatives or enemas). The ecology of the colon may improve with KGM supplementation because the proportion of fecal clostridia and fecal pH decreased. Additional studies are warranted that include an oncology population and a larger sample size.