Herbs & Supplements

Should I take it?

Glucomannan is a plant that grows mainly in Asia where it is known as konjac. A closely related species is called elephant-foot yam due to the exceptionally large tuber (an enlarged underground extension of the plant stem) that it produces. Each glucomannan plant produces one large tuber similar to a beet. Unlike most plants with roots that extend from the bottom of the tuber, glucomannan's roots grow from the top of the tuber, which also puts out one thick stem. Each glucomannan stem in turn, has only one leaf. A single, large, showy, but foul-smelling flower may bloom before the leaf appears. Depending on the species, the leaf may be multi-lobed or single. Glucomannan may be called snake plant because blotchy green, white, yellow, and/or brown markings on the stems resemble snake skin. Its tubers, which are usually harvested in the autumn from three-year old plants, can grow up to 10 or more pounds.

In Asia, glucomannan tubers are used widely as food. Fresh glucomannan tubers can be sliced and fried like potato chips. They may also be baked, boiled, stewed, or added to soup. Frequently, the tubers are shredded, dried, and ground to make a grainy meal (for cereal) or a powdery flour, which is often used to make noodles. Glucomannan meal or flour may also replace part of the corn meal, wheat flour, or rice flour used in cooking and baking. Mannose, a sugar extracted from glucomannan, sometimes is substituted for sugar in products for individuals with diabetes and glucomannan is used like tofu in vegetarian dishes. In Japan, a popular type of jelled candy called konnyaku is made from glucomannan.

Glucomannan has other uses, as well. A liquid form has been tested as a preservative to control bacteria that may contaminate other foods. Powdered glucomannan is used to thicken cosmetics, foods, and pharmaceuticals. Since it is broken down and absorbed in the colon instead of in the upper digestive tract where most other foods are digested, glucomannan is being studied as a way to deliver drugs to the large intestines for treating conditions such as irritable bowel syndrome. Because it is not irritating, glucomannan has also been included in artificial skin products that are used to cover large wounds and promote healing.

Dosage and Administration

Note: Taking glucomannan tablets has been associated with occasional life-threatening blockages of the throat. Individuals who decide to use it should either take capsules and swallow them with plenty of water or use a glucomannan powder that is mixed into fluids before swallowing. Glucomannan should always be taken with 8 ounces or more of water or other fluid.

In the United States, glucomannan capsules generally come in 500 mg or 650 mg strengths. Common dosing instructions are to take the recommended dose one hour to one-half hour before meals.

Common doses used in studies have included:

Use	Dose	Frequency
Laxative	3,000 mg to 4,000 mg (3 grams to 4 grams)	Once. Repeated after 12 hours, if necessary
Diabetes	3,600 mg to 7,200 mg (3.6 grams to 7.2 grams)	Once a day
High Cholesterol	3,900 mg (3.9 grams)	Once a day
Weight loss (Adults)	1,000 mg (one gram)	Three times a day
Weight loss (Children)	700 mg to 1,000 mg (0.7 grams to one gram)	Three times a day

Summary

Glucomannan, the fiber obtained from the tubers of the konjac plant, is used mainly as a laxative. It may also encourage weight loss, help to lower blood sugar levels, and lessen cholesterol in the blood.

Risks

Individuals with diabetes should not take glucomannan due to possible changes in blood sugar that it may cause. Children under the age of 5 and women who are pregnant or breastfeeding may want to avoid using glucomannan, as well.

Side Effects

In tablet form, glucomannan has been associated with esophageal blockages.

Interactions

Glucomannan's potential decreasing effect on blood sugar may increase the effects of drugs or herbs that also lower blood sugar.

Last Revised April 11, 2008