Glucomannan is a water-soluble dietary fibre that is derived from konjac root (Amorphophallus konjac), which grows in only certain parts of the world, including some regions in China and Japan. . Its chemical constituent is a hydrocolloidal polysaccharide comprised of 60% D- mannose and 40% D-glucose.

Konjac flour has a long history of use in both China and Japan as a food substance and as a folk remedy. Glucomannan products are widely used in Japan and China as general health aids, topically, for skin care and as a thickening agent for foods, among other things. Glucomannan, sometimes called konjac mannan, is marketed in the North America as a dietary supplement.

Glucomannan has been shown to have laxative activity. It may also have activity in the control of serum glucose, lipid levels, and weight loss.


Laxative effect- thought to be due to the swelling of glucomannan with consequent increase in stool bulk.

Weight Loss Effect-theorized to induce a satiety feeling

Glycemic control in Type 2 diabetics- The mechanism of this effect is unclear. Glucomannan may delay stomach emptying leading to the more gradual absorption of carbohydrates therefore this can reduce the elevation of blood sugar levels after meals

Hypocholesterolemic (lipid lowering)- activity is likewise, unclear. The polysaccharide may stimulate the conversion of cholesterol to bile acids, as well as the fecal excretion of bile acids. Glucomannan may also decrease the intestinal absorption of cholesterol.


Glucomannan has demonstrated some usefulness in the management of obesity, diabetes, constipation, and hypercholesterolemia.


Weight Loss

Some studies have demonstrated that glucomannan has efficacy in the management of obesity. In an eight-week, double blind study, 20 obese subjects received 1 gram of glucomannan or placebo daily. Subjects were instructed not to change eating or exercise habits. Glucomannan-supplemented subjects had a significant mean weight loss of 5.5 pounds. Serum cholesterol and LDL cholesterol were significantly reduced, as well, in the treated group.
In another a 3-month study of severely obese patients, a special hypocaloric diet therapy by itself was tested against the same hypocaloric diet in combination with 4 grams of glucomannan (in three doses) daily. The combination therapy resulted in more significant weight loss in relation to fatty mass alone, in an overall improvement in lipid status and carbohydrate tolerance and a greater adherence to the diet. The researchers concluded: “Due to the marked ability to satiate patients and the positive metabolic effects, glucomannan diet supplements have been found to be particularly efficacious and well tolerated even in the long-term treatment of severe obesity.”

In a recent randomized, placebo-controlled metabolic trial, glucomannan was found to improve metabolic control in high-risk Type 2 diabetic patients, as measured by glucose and lipid levels and blood pressure.

In another randomized controlled trial, a total of 11 hyperlipidemic and hypertensive type 2 diabetic patients treated conventionally by a low-fat diet and drug therapy participated in a study to examine whether Konjac-mannan (KJM) fiber improves metabolic control as measured by glycemia, lipidemia, and blood pressure in high-risk type 2 diabetic patients. KJM significantly reduced the metabolic control, lowered blood lipid profiles.

Glucomannan delays stomach emptying, leading to a more gradual absorption of dietary sugar; this effect can reduce the elevation of blood sugar levels that is typical after a meal.


Like other soluble fibres, glucomannan can bind to bile acids in the gut and carry them out of the body in the feces, which requires the body to convert more cholesterol into bile acids. This can result in the lowering of blood cholesterol and other blood fats. Controlled and double-blind studies have shown that supplementation with several grams per day of glucomannan significantly reduced total blood cholesterol, LDL (�bad�) cholesterol, and triglycerides, and in some cases raised HDL (�good�) cholesterol. One double-blind study reported that glucomannan (8-13 grams per day) lowered total and LDL cholesterol in people with the insulin resistance syndrome.

Several studies have demonstrated that glucomannan is an effective treatment for many with chronic constipation. This has been demonstrated in double blind, placebo-controlled and multicenter studies. One to 4 grams daily, in divided doses, are typically used in these studies of constipation.


Glucomannan is contraindicated in those hypersensitive to any component of a glucomannan-containing product. It is also contraindicated in those with intestinal obstruction, difficulty in swallowing and esophageal narrowing.

Pregnant women and nursing mothers should avoid glucomannan supplements.
Glucomannan must be taken with adequate amounts of fluids. Inadequate fluid intake may cause glucomannan to swell and block the throat, esophagus or intestines.
Tablet forms of glucomannan should be avoided.
Glucomannan should not be taken before going to bed.
Type 2 diabetics who use glucomannan, may require adjustment of their antidiabetic medications.

A few cases of esophageal obstruction have been reported with the use of glucomannan tablets. The most common adverse reactions are flatulence and abdominal distension. Diarrhea is occasionally reported.

Fat-soluble vitamins (A, D, E, K): Concomitant intake of fat soluble vitamins and glucomannan may decrease the absorption of the fat-soluble vitamins.
Glucomannan may decrease the absorption of fat-soluble vitamins found in foods.
Glucomannan supplements are mainly available in capsules. Glucomannan powder is also available and there are glucomannan combination products.
Doses used range from one to four grams daily, taken in divided doses and with plenty of liquids.



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