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What is glucomannan? Why do we need it?

Glucomannan is a water-soluble dietary fiber derived from the konjac root, a Japanese plant. The plant is cleaned, and the fiber is purified before being used as a supplement.

The main uses of glucomannan are to promote larger stools and improve digestion. Studies conducted on individuals suffering from constipation have shown that glucomannan supplementation helps produce a bowel movement within 12 to 24 hours. Glucomannan also delays the emptying of stomach contents, which allows for a more gradual absorption of dietary sugar, and can reduce blood sugar levels. As a result, some scientists believe that glucomannan can be used to help treat diabetes and related conditions.

Because glucomannan is a soluble fiber, it can bind to certain acids produced in the stomach and remove them from the body. In this way, it can help lower blood cholesterol and blood lipid levels. Controlled studies have shown that glucomannan can reduce levels of total blood cholesterol, LDL (or "bad") cholesterol, and triglycerides, and may even raise levels of HDL ("good") cholesterol. Glucomannan may also help promote weight loss.

How much glucomannan should I take?

The amount of glucomannan to be consumed depends on the condition being treated. A basic guide for glucomannan supplementation is as follows:

  • Laxative: 3-4 grams per day
  • Lowering blood cholesterol: 4-13 grams per day
  • Controlling blood sugar: 500-700 milligrams per 100 calories in one's daily diet
  • Weight loss: 1-3 grams before each meal

It is also recommended that patients drink at least eight ounces of water each time they consume any bulk-forming laxative such as glucomannan.

What forms of glucomannan are available?

Glucomannan is available as a bulk powder and as a type of capsule. It is not known if any foods contain significant amounts of glucomannan.

What can happen if I take too much glucomannan? Are there any interactions I should be aware of? What precautions should I take?

Because glucomannan expands rapidly, patients with any disorder of the esophagus should avoid taking glucomannan or any other fiber supplement in pill form. Supplementing with glucomannan may also result in flatulence and abdominal discomfort, especially in people unaccustomed to a high-fiber diet. There is also evidence that some people may have an allergic reaction to glucommanan powder. If an allergic reaction occurs, discontinue use.

As of this writing, there are no well-known drug interactions associated with glucomannan. As always, make sure to consult with a licensed health care provider before taking glucomannan or any other herbal remedy or dietary supplement.


  • Arvill A, Bodin L. Effect of short-term ingestion of konjac glucomannan on serum cholesterol in healthy men. Am J Clin Nutr 1995;61:585-9.
  • Chen HL, Sheu WH. Konjac glucomannan supplement alleviated hypercholesterolemia and hyperglycemia in type 2 diabetic subjects - a randomized double-blind trial. J Am Coll Nutr Feb 2003;22(1):36-42.
  • Loening-Baucke V. Fiber (glucomannan) is beneficial in the treatment of childhood constipation. Pediatrics March 2004;113(3):e259-64.
  • Staianno A, Simeone D, Giudice ED, et al. Effect of the dietary fiber glucomannan on chronic constipation in neurologically impaired children. J Pediatr 2000;136:41-5.
  • Wu J, Peng SS. Comparison of hypolipidemic effect of refined konjac meal with several common dietary fibers and their mechanisms of action. Biomed Environ Sci 1997;10:27-37.
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