Glucomannan is a water-soluble polysaccharide composing 40% by dry weight of the roots or corm of the konjac plant. Glucomannan is a dietary fiber, and has been marketed as a treatment for constipation, obesity, high cholesterol, Acne vulgaris (source) and Type 2 diabetes. Glucomannan is also a hemicellulose that is present in large amounts in the wood of conifers and in smaller amounts in the wood of dicotyledons.

Reported uses

Glucomannan is used to manage constipation, diabetes, obesity, hypercholesterolemia, and hyperlipidemia. It's also used to induce weight loss.

Administration

For diabetes: 3.6 to 7.2 g by mouth every day

For hyperlipidemia: 3.9 g by mouth every day

For weight loss: 1 g by mouth three times a day, 2 hours before each meal.

Hazards

Adverse reactions associated with glucomannan include esophageal obstruction, flatulence, diarrhea, and hypoglycemia. Glucomannan may cause significant hypoglycemia when given with oral antidiabetics or insulin. The fiber content of glucomannan may interfere with the absorption of various drugs.

Patients with a history of an allergic reaction to glucomannan or any of its components should avoid use. Patients with GI dysfunction, patients prone to hypoglycemia, and patients with underlying diabetes should use with caution.

Clinical considerations

Consuming glucomannan may result in a feeling of fullness, thereby decreasing the appetite.

Monitor patient for adverse effects such as esophageal obstruction, lower GI obstruction, flatulence, diarrhea, and hypoglycemia.

Monitor patient's weight and serum cholesterol and serum glucose levels.

Advise patient to avoid using tablet form because it poses an increased risk of esophageal obstruction.

Inform patient that the therapeutic and toxic components of glucomannan can vary significantly from product to Product. Advise him to obtain glucomannan from a reliable source.

Advise patient to separate administration times by at least 2 hours because glucomannan may interfere with the absorption of medications.

Tell patient to notify pharmacist of any herbal or dietary supplement that he's taking when obtaining a new prescription.

Advise patient to consult his health care provider before using an herbal preparation because a conventional treatment with proven efficacy may be available.

Glucomannan Dosage

Typical dosage recommendations for glucomannan are 1 gram consumed with at least 8 ounces of water approximately one hour prior to a meal (can be repeated 3-4 times per day at each meal). If combined with other fibers, follow the directions on the specific product because different fiber products may have different dosage/use recommendations.

Research summary

Konjac mannan (glucomannan) has been shown to possess many of the pharmacologic characteristics of other polysaccharides. In large doses it has laxative activity and may alter the metabolism of microflora in the intestine. Konjac mannan may be effective in reducing serum cholesterollevels. There is conflicting evidence regarding its use as a weightreduction aid though it does appear to alter lipid metabolism.