Scientific Name: Glucomannan

Other Names: Amorphophallus konjac, Devil's Tongue, Elephant-foot Yam, Konjac, Konjac Mannan, Konnyaku, Snake Plant

Who is this for?

Glucomannan is the Western name for vegetable fibers derived from an Asiatic plant family known as konjac. Glucomannan does not dissolve in water, but forms a thick, gooey gel when exposed to fluids. The body does not digest glucomannan, so the resulting large soft mass moves through the intestines and may trigger intestinal muscle contractions. Therefore, glucomannan is thought to be an effective bulk-type laxative, even though the process may take up to 12 hours.

Glucomannan has also been studied for treating obesity, diabetes, and high cholesterol. Studies in both adults and children with severe obesity showed varying degrees of weight loss associated either with taking supplemental glucomannan or with replacing some of the usual diet with foods made from glucomannan (konjac) flour — the dried and ground tuber (underground stem) of the plant. Generally, it is believed that glucomannan discourages overeating because it creates a feeling of fullness that persists because the fiber in it swells and stomach contents stay in the stomach longer. In most of the research studying glucomannan for weight loss, participants also drank increased quantities of water and followed a reduced-calorie diet.

Possibly due to the same delay in stomach emptying, glucomannan may improve blood sugar levels in individuals with diabetes. Because the absorption of carbohydrates from foods is slower when glucomannan is taken, blood sugar levels may not rise as high or as fast as usual. Some preliminary results from animal studies also suggest that glucomannan may increase the sensitivity of body tissues to the insulin that is produced or taken. In several studies, taking glucomannan has also appeared to lower blood levels of total cholesterol, low-density lipoproteins (LDL, or "bad" cholesterol), and triglycerides. Although more research on this possible use of glucomannan is needed, it is believed that glucomannan may increase the elimination of cholesterol and its components from the body. It may also keep bile acids from being reabsorbed in the intestines, further reducing cholesterol levels in the blood, because the body uses cholesterol to produce more bile.

When should I be careful taking it?

Although glucomannan has been studied in children as young as 5 years old, very little information is available on how glucomannan might affect a developing fetus, an infant, or a small child. Therefore, its use is not recommended during pregnancy, while breast-feeding, or before the age of 5.

Individuals with diabetes should avoid using large amounts of glucomannan because it may lower blood sugar levels, potentially resulting in hypoglycemia (blood sugar that is too low). Symptoms of low blood sugar include shakiness, sweating, confusion, distorted speech, and loss of muscle control. If not corrected, low blood sugar can lead to unconsciousness and even death.

What side effects should I watch for?

Glucomannan tablets are not recommended for oral use. Reportedly, several individuals experienced blockage of the esophagus when they took glucomannan in tablet form. The tablets lodged in their throats and swelled when exposed to water. Although no cases have been reported, the potential for a similar blockage of the intestines exists.

One case of allergic pneumonia caused by inhaling glucomannan dust has been documented in an individual who worked for over 35 years in a factory that produced glucomannan powder.

What interactions should I watch for?

Glucomannan's possible lowering effect on blood sugar may intensify the effects of insulin and oral drugs for diabetes, such as:

• Actos
• Amaryl
• Avandia
• glipizide (Glucotrol XL)
• glyburide (Glynase)
• Glyset
• metformin (Glucophage)
• Prandin
• Precose

When mixed with water or other fluids, glucomannan forms a sticky, slippery gel that may coat the stomach and intestines. In theory, taking glucomannan by mouth could block the absorption of drugs, herbal products, other dietary supplements, or nutrients from foods that are taken at the same time. If you take glucomannan, do not take drugs or herbals within 2 hours.

Because glucomannan may decrease blood sugar levels, taking it with other blood sugar-lowering herbal products may result in hypoglycemia — blood sugar that is too low. Herbals that may reduce blood sugar include:

• Eleuthero
• Fenugreek
• Ginger (in high amounts)
• Kudzu
• Panax ginseng

Some interactions between herbal products and medications can be more severe than others. The best way for you to avoid harmful interactions is to tell your doctor and/or pharmacist what medications you are currently taking, including any over-the-counter products, vitamins, and herbals.

Should I take it?

Glucomannan is a plant that grows mainly in Asia where it is known as konjac. A closely related species is known as 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 leaves 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. Tubers, which are usually harvested in the autumn from three-year old plants, can grow up to 10 or more pounds.

In parts of Asia, individuals slice and fry fresh glucomannan tubers like potato chips. More frequently, the tubers are shredded, dried, and ground to make a grainy meal 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, is sometimes substituted for sugar in products for individuals with diabetes. In Japan, a popular type of jelled candy called konnyaku is made from glucomannan. A liquid form of glucomannan has been tested as a preservative to control bacteria that may contaminate other foods. Powdered glucomannan is used to thicken cosmetics, foods, and pharmaceuticals.

Dosage and Administration

Note: Taking glucomannan tablets has been associated with occasional life-threatening blockages of the throat. If you decide to use it, take glucomannan as 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.

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 breast-feeding 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 interfere with drugs or herbs that also lower blood sugar.

Last Revised June 1, 2004

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