Glucomannan
Scientific Name(s): Amorphophallus konjac Koch. Family: Araceae
Common Name(s): Konjac , Konjac mannan , glucomannan
Clinical Overview
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Uses of Glucomannan
Glucomannan reportedly alleviates constipation, reduces intestinal flora, lowers blood sugar and cholesterol and may possibly promote weight loss and inhibit cancer.
Glucomannan Dosing
Clinical studies of glucomannan in diabetes, cholesterol control, and obesity have used doses of 2-13 g daily.
Contraindications
Use with great caution in patients with diabetes.
Pregnancy/Lactation
Information regarding safety and efficacy in pregnancy and lactation is lacking.
Glucomannan Interactions
None well documented.
Glucomannan Adverse Reactions
Severe esophageal and GI obstruction have been reported due to glucomannan tablets. The hypoglycemic effects are potentially dangerous to diabetics.
Toxicology
Research reveals little or no information regarding toxicology with the use of this product.
Konjac mannan is a polysaccharide derived from the tubers of konjac. It is purified from konjac flour by repeated treatment with cupric hydroxide and subsequent washings with ethanol 1 or by dialysis against water. 2 , 3
Chemistry
Glucomannan is composed of glucose and mannose combined by beta-1,4 glucosidic linkages in a molecular ratio of 1:1.6 and is often referred to as glucomannan. The polysaccharide is easily “denatured” through enzymatic cleavage or treatment with weak alkaline solutions, becoming irreversibly water insoluble. In Japan, this coagulated product is called “konnyaku” and is commonly used as a foodstuff.
Glucomannan Uses and Pharmacology
GI effectsPolysaccharides such as guar gum (composed of galactose and mannose; galactomannan), tragacanth, cellulose, methylcellulose, pectin, and wheat bran have found use as foodstuffs and, more recently, as dietary and therapeutic agents. Their ability to swell by the absorption of water has made them useful as laxatives.
Animal dataKonjac mannan has been reported to alleviate moderate constipation in 1 to 2 days and reduces fecal flora by a factor of 1000 in 10 days. Research on microflora in mice and rats suggests that a diet that includes konjac mannan alters the microbial metabolism in the intestine. 4 The study noted that in animals bearing human microflora, the differences in microbial composition were only slight despite the metabolic differences observed.
Clinical dataResearch reveals no clinical data regarding the use of glucomannan for GI effects.
Blood sugar lowering effectsBy increasing the viscosity of the intestinal contents, slowing gastric emptying time, and acting as a barrier to diffusion, agents such as guar gum have been shown to delay the absorption of glucose from the intestines. 5
Animal dataResearch reveals no animal data regarding the use of glucomannan for blood sugar lowering effects.
Clinical dataSeveral small studies have shown that diabetics fed a diet consisting largely of raw vegetables, uncooked seeds, fruits and goat's milk, were able to reduce or discontinue their insulin requirements. 6 Similarly, konjac mannan has been reported to reduce the need for hypoglycemic agents. When 13 diabetic patients received 3.6 or 7.2 g of konjac mannan daily for 90 days, their mean fasting glucose levels fell by 29% and insulin or hypoglycemic agent doses were reduced in most patients. 7 Five healthy men enrolled in the same study underwent a glucose tolerance test with or without a single dose of 2.6 g konjac mannan. The polysaccharide reduced mean blood glucose levels by 7.3% at 30 minutes with a concomitant decrease in serum insulin concentration. Another study of 72 type II diabetic patients showed a significant reduction in fasting blood glucose and postprandial blood glucose after consuming konjac food 30 and 65 days. 8
Weight reductionAnimal data
Research reveals no animal data regarding the use of glucomannan for weight reduction.
Clinical dataKonjac mannan is gaining popularity as a weight-reducing agent and is often included in “grapefruit diet” tablets. One U.S. patent claims that its use resulted in weight loss without appetite changes; however, no weights were reported. Some research has indicated that patients treated with oral glucomannan have decreased body weight compared with control groups. In one study involving an 8-week cardiac rehabilitation program, patients were given 1.5 grams of glucomannan twice daily. 9 Body weight among treated patients decreased by 1.5 kg at the end of 4 weeks and by 2.2 kg at the end of 8 weeks. These losses were significant when compared with the placebo group. In contrast, other research conducted with overweight children has found no significant difference in weight loss between children treated with 1 g glucomannan twice daily and those given a placebo. 10
Hydrophilic gums have found some use as diet aids based on the theory that the feeling of fullness provided by their swelling leads to a decrease in appetite. Such agents are generally considered to be only marginally effective.
Cholesterol lowering effectsThe activity of this polysaccharide cannot be explained by a simple interaction with bile acids since konjac mannan shows no in vitro or in vivo bile-binding activity. Rather, it appears to inhibit the active transport of cholesterol in the jejunum and the absorption of bile acids in the ileum. 11
Animal dataKonjac mannan has been shown to reduce plasma cholesterol levels in rats. 12 Interestingly, only water-soluble konjac mannan retains this effect. The hypocholesteremic effect is completely eliminated when the mannan is coagulated to a water-insoluble form. Rats fed high cholesterol diets containing 3% crude konjac mannan for 7 days exhibited plasma cholesterol levels 16% lower than control rats fed only the high cholesterol diet. Rats fed highly purified konjac mannan had plasma cholesterol levels 23% lower than the controls. Rats treated with konjac mannan that had been coagulated with cellulase had mean cholesterol levels greater than the controls. The implication is that the foodstuff konnyaku (coagulated water-insoluble product) most likely has no cholesterol-reducing activity. A study on bile output in rats fed a diet of 5% konjac mannan showed an increase in the volume of bile juice secreted and the release of bile acids, protease and amylase compared to animals fed a control diet without fiber. 13 This effect was only observed for prolonged feeding of the experimental diet with konjac mannan and could not be produced with a single dose.
Clinical dataIn a study of 10 overweight patients, the daily administration of 100 ml of 1% solution of konjac mannan for 11 weeks resulted in decreases in serum cholesterol levels of 0% to 39% (mean, 18%). 2 In a separate double-blind crossover trial involving 63 men, total cholesterol was reduced by 10% among subjects given a daily dose of 3.9 g of konjac glucomannan for a 4-week period. 14 Interestingly, no significant change in high-density lipoprotein (HDL) cholesterol was observed as a result of the treatment. The diabetic patients treated in another study 7 showed a reduction in mean serum cholesterol levels of 11% after 20 days of konjac mannan treatment. Several other studies confirm the effects of konjac mannan on lipid metabolism. 15 , 16 , 17
Lung cancerAnimal data
A Chinese study has investigated the ability of konjac powder to inhibit lung cancers in mice. 18 Mice fed a diet of 8% Konjaku powder, mixed in with a common diet, showed a reduction in cancer rate from 70.87% in the positive control group to 19.38% in the group fed with konjac powder. Lung tumors were induced with MNNG. The study reported no adverse reactions to the konjaku powder. 18
Clinical dataResearch reveals no clinical data regarding the use of glucomannan for lung cancer.
Dosage
Clinical studies of glucomannan in diabetes, cholesterol control, and obesity have used doses of 2-13 g daily. 19 , 20 , 21 , 22
Pregnancy/Lactation
Information regarding safety and efficacy in pregnancy and lactation is lacking.
Interactions
None well documented.
Adverse Reactions
Four cases of severe esophageal obstruction due to glucomannan diet tablets have been reported. 23 , 24 Seven additional cases were noted during 1984/85 by the Australian Adverse Drug Reactions Advisory Committee. 25 Glucomannan-containing tablets have been banned in Australia since May 1985 because these also carry the potential for inducing lower gastrointestinal obstruction. Encapsulated and powder forms remain available.
Glucomannan use is associated with a reduction in the need for hypoglycemic agents, and the product may result in a loss of glycemic control in diabetic patients. It should be used with great care by diabetic patients.
Toxicology
Research reveals little or no information regarding toxicology with the use of this product.
Bibliography
1. Kiriyama S, et al. J Nutr 1972;102(12):1689.2. Sugiyama N, Shimahara H, inventors; Kabushiki Kaisha Shimizu Manzo Shoten, assignee. Konjac mannan. US patent 3 973 008. August 3, 1976.
3. Sugiyama N, Shimahara H, inventors; Kabushiki Kaisha Shimizu Manzo Shoten, assignee. Method of reducing serum cholesterol level with extract of konjac mannan. US patent 3 856 945. December 24, 1974.
4. Fujiwara S, et al. Food Chem Toxicol 1991;29(9):601.
5. Jenkins DJ, et al. Br Med J 1978;1(6124):1392.
6. Anonymous. Med Letter 1979;21(12):51
7. Doi K, et al. Lancet 1979;1(May 5):987
8. Huang CY, et al. Biomed Environ Sci 1990;3(2):123.
9. Reffo GC, et al. Curr Ther Res 1990;47(May):753.
10. Vido L, et al. Padiatr Padol 1993;28(5):133.
11. Kiriyama S, et al. J Nutr 1974;104(1):69
12. Kiriyama S, et al. J Nutr 1969;97(3):382
13. Ikegami S, et al. J Nutr Sci Vitaminol 1984;30(6):515.
14. Arvill A, Bodin L. Am J Clin Nutr 1995;61(3):585.
15. Zhang MY, et al. Biomed Environ Sci 1990;3(1):99.
16. Hou YH, et al. Biomed Environ Sci 1990;3(3):306.
17. Shimizu H, et al. J Pharmacobiodyn 1991;14(7):371.
18. Luo DY. Chung-Hua Chung Liu Tsa Chih [Chin J Oncol] 1992;14(1):48.
19. Chen HL, Sheu WH, Tai TS, Liaw YP, Chen YC. Konjac supplement alleviated hypercholesterolemia and hyperglycemia in type 2 diabetic subjects--a randomized double-blind trial. J Am Coll Nutr. 2003 ;22:36-42.
20. Vuksan V, Sievenpiper JL, Owen R, et al. Beneficial effects of viscous dietary fiber from Konjac-mannan in subjects with the insulin resistance syndrome: results of a controlled metabolic trial. Diabetes Care . 2000;23:9-14.
21. Marsicano LJ, Berrizbeitia ML, Mondelo A. [Use of glucomannan dietary fiber in changes in intestinal habit]. G E N . 1995;49:7-14.
22. Walsh DE, Yaghoubian V, Behforooz A. Effect of glucomannan on obese patients: a clinical study. Int J Obes . 1984;8:289-293.
23. Fung M. Med J Austr 1984;140(6):350.
24. Gaudry P. Med J Austr 1985;142(3):204.
25. Henry DA, et al. Br Med J 1986;292(6520):591.
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