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Glucomannan

Scientific Name(s): Amorphophallus konjac Koch., Amorphophallus rivieri Durieu ex Riviére.
Common Name(s): Glucomannan, Gonyak, Konjac, Konjac mannan, Konnyaku

Medically reviewed by Drugs.com. Last updated on May 21, 2024.

Clinical Overview

Use

Glucomannan has been investigated for its effects on weight reduction, diabetes, constipation, cholesterol, lung cancer, and atopic diseases, as well as its use as a prebiotic. There are issues of quality concerning the evidence to support use for these indications.

Dosing

Clinical studies of glucomannan in diabetes, cholesterol control, and obesity have used dosages of 1 to 13 g daily.

Contraindications

Given the risk of esophageal and gastric obstruction, use is not recommended in patients with structural abnormalities of the esophagus or gut.

Pregnancy/Lactation

Information regarding use during pregnancy and lactation is lacking. Until more information is obtained, use is not recommended in pregnant or breast-feeding women.

Interactions

Because of glucomannan's potential ability to lower blood glucose, use caution in patients receiving oral hypoglycemic agents, insulin, or alternative medicines that could potentially lower glucose levels. Additionally, glucomannan may reduce the bioavailability of other oral medications. Thus, it is recommended that other medications be taken 1 hour before or 4 hours after glucomannan administration.

Adverse Reactions

Severe esophageal and GI obstruction have been reported with glucomannan tablets. The hypoglycemic effects are potentially dangerous to patients with diabetes. Glucomannan has been linked in case reports to cholestatic hepatitis and occupational asthma. Minor adverse effects are normally GI related and include diarrhea, flatulence, abdominal discomfort, and bloating.

Toxicology

Glucomannan given at 500 mg/kg/day for 18 months to rats demonstrated no toxicity. Data suggest diarrhea, abdominal pain, and flatulence occur with dosages more than 5 g daily.

Scientific Family

Source

Konjac mannan is a polysaccharide derived from the tubers or roots of the elephant yam or konjac.1 It is purified from konjac flour by repeated treatment with cupric hydroxide and subsequent washings with ethanol2 or by dialysis against water.3, 4 The plant is widely grown in southern and southeastern China and Vietnam. It grows well in shady environments in seasonal temperatures of 5° to 43°C (41° to 109°F).5

History

Konjac glucomannan was first used and studied by the Chinese, and its medicinal properties were first described in the Shen Nong Materia Medica during the Western Han Dynasty (ca 206 BC to 08 AD). Konjac flour has been traditionally produced through processing corms, the underground storage organs. After boiling with plant ash, the flour is consumed as cake or gel.5 Its therapeutic effects are believed to be due to serotonin. Chinese people have used konjac glucomannan for over 2,000 years to treat conditions such as asthma, cough, hernia, breast pain, burns, and hematological and skin diseases. The leaves have also been used as an insect repellent. In the 6th century AD, konjac glucomannan was introduced to Japan as a medicinal product.5

Glucomannan is commonly used in foods, drinks, and cosmetics for its gelling properties. It has been approved by the Food and Drug Administration (FDA) since 1994 as a food additive and since 1996 as a binder in meat products. China is the largest producer of konjac, and Japan is the second largest. In China, approximately 400 factories manufacture konjac flour.5

Chemistry

Glucomannan is a water-soluble, fermentable dietary fiber composed of mannose and glucose combined by beta-1,4 glucosidic linkages in a molar ratio of 1.6:1.1 Compared with other dietary fibers, it has the highest viscosity and molecular weight, ranging from 200,000 to 2,000,000 Da, which varies with origin, method of processing, and storage time.5 Glucomannan possesses hygroscopic properties. The dry formulation swells into a viscous gel in hot or cold water, absorbing up to 50 times its weight when in water.1, 5, 6 A viscous gel forms at pH levels between 4 and 7.5, 6 The polysaccharide is easily "denatured" through enzymatic cleavage or treatment with weak alkaline solutions, becoming irreversibly water insoluble. Glucomannan was once believed to be nonbiodegradable; however, certain gut flora bacteria such as Aerobacter mannaolyticus, Clostridium butyricum, and Clostridium beijerinckii contain endo-beta-mannanases that catalyze the degradation of glucomannan into disaccharides and eventually to glucose and mannose.7 Heat and mechanical agitation enhance the solubility of glucomannan. In Japan, this coagulated product is called "konnyaku" and is commonly used as a foodstuff. In Korea, it is referred to as "gonyak."5

Amorphophallus konjac as dormant corms contains various components including the following: 49% to 60% w/w glucomannan, 10% to 30% w/w starch, inorganic elements, 5% to 14% w/w crude protein, 3% to 5% w/w soluble sugars, and 3.4% to 5.3% w/w ash. Fresh corms contain organic compounds, including beta-carotene, choline, niacin, riboflavin, and thiamine. In addition, serotonin and its derivatives have been found in fresh corms.5

Uses and Pharmacology

GI effects

Polysaccharides, such as glucomannan, 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. Additionally, konjac glucomannan has been investigated for its role as a prebiotic, an agent that stimulates the growth and activity of beneficial gut flora, including Bifidobacterium and Lactobacillus species.8

Animal data

Konjac mannan has been reported to alleviate moderate constipation in 1 to 2 days and reduces fecal flora by a factor of 1,000 in 10 days. Research on microflora in mice and rats suggests a diet that includes konjac mannan alters microbial metabolism in the intestine.9 The study noted that in animals bearing human microflora, the differences in microbial composition were only slight despite the metabolic differences observed. A study determined that both unhydrolyzed konjac glucomannan and konjac glucomannan hydrolysate increased cecal anaerobes and bifidobacteria in Balb/c mice at 2 and 4 weeks following dietary consumption. Of note, glucomannan hydrolysate had a 2- to 4-fold larger anaerobe count at 4 weeks compared with unhydrolyzed glucomannan and cellulose treatment groups. Both unhydrolyzed glucomannan and glucomannan hydrolysate decreased cecal Clostridium perfringens, a potentially harmful bacterium, at week 4. Both of these compounds modulated fecal and cecal flora in a dose-dependent fashion.8 In another similar study, 5% w/v konjac glucomannan hydrolysate fed to Wister mice for 14 weeks stimulated the growth of fecal anaerobes and lactobacilli compared with the control group (P < 0.001). The compound was also able to decrease counts of fecal Escherichia coli and C. perfringens.10

Clinical data

Konjac glucomannan's effects on human bowel habits were assessed in a study of healthy adults. Eight adult volunteers (21 to 54 years of age) followed the study design of 3 weeks of placebo and 1 week of adaptation in which konjac glucomannan was titrated from 1.5 to 3 g daily and was maintained at 4.5 g daily during the 3-week treatment period. On days 15 to 21 of the placebo and treatment periods, all stools were collected. Diet was controlled by having the patients adhere to a 7-day cycle menu, consisting of various low-fiber Chinese foods throughout the entire study. The mean frequency of defecation was increased by 27% following supplementation with konjac glucomannan (P < 0.05). Additionally, the ease of passage of stool also improved with treatment (P < 0.05).

Supplementation with konjac glucomannan significantly increased fecal lactobacillus concentrations (P < 0.05), total bacteria concentrations (P < 0.05), and bifidobacteria output (P < 0.05). Supplementation did not cause abdominal cramping, bloating, or flatulence.11 The same investigators performed a similarly designed study with 7 constipated women. Supplementation with konjac glucomannan led to an increase in defecation each week (4.1 ± 0.6 to 5.3 ± 0.6). The fecal weight wet was not impacted by fiber supplementation, while the fecal dry weight was increased. Supplementation also increased the fecal output of bifidobacteria, lactobacilli, and total bacteria.12

In a randomized, double-blind, crossover study, the laxative effects of glucomannan were assessed in 31 children (4.5 to 11.7 years of age) with long-term constipation with or without encopresis. Patients were given placebo and glucomannan 100 mg/kg body weight up to 5 g daily with 50 mL of fluid per 500 mg. Each patient received glucomannan or placebo for 4 weeks and then the other treatment for 4 weeks. Treatment with glucomanna was associated with improvements in stool consistency and soiling episodes as well as frequency of bowel movements when compared with the initial evaluation (P < 0.03). Forty-five percent of participants experienced successful treatment on glucomannan when compared with placebo (13%, P < 0.02). No side effects were reported by the participants.13

Konjac glucomannan 1.26 g twice daily for 4 weeks was demonstrated to be no better than placebo at relieving pain in children with abdominal pain-related functional GI disorders, the majority of whom are subsequently diagnosed with conditions such as irritable bowel syndrome or functional dyspepsia. This double-blind randomized clinical trial (n = 84) also found no differences in secondary outcomes that included abdominal cramps, bloating, nausea, vomiting, or stool consistency.56 Another placebo-controlled 4-week study evaluated the same dose in children (n = 72 evaluable) with functional constipation. There was no significant difference between glucomannan and placebo groups in response to constipation, defined as 3 or more stools per week without soiling. Adverse event rates, and use of rescue medication (lactulose) were similar between groups.57

Antidiabetic effects

By increasing the viscosity of the intestinal contents and slowing gastric emptying time, glucomannan is able to reduce postprandial glucose levels and attenuate insulin surges. This likely improves peripheral insulin sensitivity.14, 15

Animal data

In a streptozotocin-induced model of diabetes in pancreatic islets of mice, 3 oligosaccharide fractions from A. konjac were isolated and assessed for their effects on free radical regulation and insulin secretion. Only 1 of the fractions, KOS-A, at concentrations of less than 1.5 mM decreased nitric oxide levels in the islets but did not affect normal nitric oxide release. Additionally, at this concentration, KOS-A did not alter normal insulin secretion.16

Clinical data

Several 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 requirement.17 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.18 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 2 diabetic patients showed a reduction in fasting blood glucose and postprandial blood glucose after consuming konjac food 30 and 65 days.19

In 20 patients with type 2 diabetes, glucomannan 1 g given 30 minutes prior to an oral glucose tolerance test reduced prandial ghrelin levels, a hormone that increases appetite and the intake of food. However, this reduction was not statistically significant when compared with a standard glucose load or white rice load.20

In 2008, a meta-analysis determined that glucomannan significantly affected fasting blood glucose (weighted mean difference, −7.44 mg/dL; 95% confidence interval [CI], −14.16 to −0.72).21

Weight reduction effects

Upon oral administration, glucomannan passes mostly unchanged into the colon as human salivary and pancreatic amylase enzymes are unable to split the beta-1,4 glucosidic linkages. The polysaccharide is believed to cause weight loss by promoting satiety, delaying gastric emptying time, slowing small-bowel transit time, attenuating postprandial insulin surges, and increasing levels of plasma cholecystokinin.1

Animal data

Research reveals no animal data regarding the use of glucomannan for weight reduction.

Clinical data

Konjac mannan is often included in "grapefruit diet" tablets. One US 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 1 study involving an 8-week cardiac rehabilitation program, patients were given 1.5 g of glucomannan twice daily.22 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. Another showed that inclusion of resistance (1 hour) and endurance (30 minutes) exercise performed 3 times each week in combination with 3 g of glucomannan for 8 weeks was able to augment a reduction in fat mass (ie, 63% in men, 50% in women) as well as waist circumference; however, it did not affect body mass or body mass index. Cholesterol parameters also improved.23 Overweight and moderately obese adults (n = 53) with body mass indices of 25 to 35 kg/m2 randomly assigned to placebo or glucomannan 1.33 g 3 times daily for 8 weeks did not exhibit any significant difference in weight loss or other outcomes (ie, body composition, hunger, fasting lipids, blood glucose) between groups by the end of the trial.60

Glucomannan's effects on weight reduction have been evaluated in children. Research conducted in 60 children younger than 15 years (mean age, 11.2 years; mean overweight, 46%) found that glucomannan given 1 g twice daily for 2 months to 30 children reduced mean weight from 49.5% to 41% (P < 0.01). Similarly, 30 children received placebo and the mean weight decreased from 43.9% to 41.7% (P < 0.01). However, there were no statistically significant differences between the treatment and placebo groups.24, 25 Another study found that when compared with a control group, glucomannan given at dosages of 2 to 3 g daily for 4 months reduced excess body weight, total cholesterol, and triglycerides in obese children. A randomized, placebo-controlled, 8-week pediatric study (n =120, age 9 ±4 years) evaluated two 1.2 mg chromium products, chromium polynicotinate (CPNC) and chromium policosanol (CPC), and glucomanna (GM) 500 mg in hypercholesterolemia. Patients were randomized to 1 of 5 groups: placebo, CPNC, CPC, GM, CPNC with GM, or CPC with GM. No significant lipid lowering benefit was seen with any of the 3 monotherapy groups (CPNC, CPC, GM). The CPNC-GM group, but not the CPC-GM group, had significant reductions in total cholesterol and low-density lipoprotein-cholesterol (LDL-C).25, 26, 58

A meta-analysis of clinical trials conducted in overweight and obese patients (9 studies, n = 237) found a nonsignificant weight loss of 0.22 kg (95% confidence interval [CI], −0.62 to 0.19 kg). The authors cited flaws in published studies including insufficient detail on randomization concealment methods and brief study duration (just 3 weeks for 2 of the included studies).59 This finding of nonsignificance varies from another meta-analysis published in 2008,21 but the more recent review included only weight loss data from studies in overweight and obese patients.

A novel polysaccharide, PolyGlycopleX or PGX, has been developed by reacting glucomannan with various polysaccharides. This new compound possesses the highest viscosity and water-holding properties compared with other fibers. In a study of 29 overweight or obese adults, PGX supplemented 2 to 3 times daily before meals for 14 weeks significantly reduced weight (−5.79 ± 3.55 kg), waist circumference (−12.07 ± 5.56 cm), and percentage of body fat (−2.43 ± 2.39%) when compared with baseline values (P < 0.05). Specifically, women experienced an average weight loss of 5.14 ± 3.49 kg and men 8.30 ± 2.79 kg. Total cholesterol, LDL-C, and fasting blood glucose levels were also reduced.27

Effects on lipids

The activity of konjac mannan cannot be explained by a simple interaction with bile acids because it shows no in vitro or in vivo bile acid–binding activity. Rather, it appears to inhibit the active transport of cholesterol in the jejunum and the absorption of bile acids in the ileum, yielding improvements in plasma LDL and apolipoprotein B levels.15, 28 It has also been suggested that glucomannan increases the activity of 7-alpha-hydroxylase, an enzyme required for cholesterol conversion to bile acids.29

Animal data

Konjac mannan reduced plasma cholesterol levels in rats30; however, only water-soluble konjac mannan had 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 controls. Rats fed highly-purified konjac mannan had plasma cholesterol levels 23% lower than 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 with animals fed a control diet without fiber.31 This effect was only observed after prolonged feeding of the experimental diet with konjac mannan and could not be produced with a single dose.

Clinical data

In a study of 10 overweight patients, the daily administration of 100 mL of 1% solution of konjac mannan for 11 weeks resulted in a mean decrease in serum cholesterol levels of approximately 18%.3 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.32 No change in high-density lipoprotein (HDL) cholesterol was observed as a result of the treatment. The diabetic patients treated in another study18 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.33, 34, 35

In a double-blind, placebo-controlled, parallel study, 30 overweight and obese men received glucomannan 3 g daily (n = 15) or placebo (n = 15) for 12 weeks. From baseline to 12 weeks, a reduction in total cholesterol (−10%, −6.3%), plasma triglycerides (−35.%, −42.5%), and increase in HDL cholesterol (−12.3%, −6%) levels occurred in the glucomannan and placebo groups, respectively. No differences were noted between groups. LDL cholesterol levels declined from baseline to 6 weeks in the glucomannan group but not in the placebo group; however, at 12 weeks, both groups experienced a reduction compared with baseline (−14.1% for glucomannan compared with −6% for placebo). Additionally, this study also determined that glucomannan reduced body weight, percent body fat, systolic blood pressure, waist circumference, and glucose levels.36

A meta-analysis published in 2008 evaluated 14 studies with a total of 531 patients and suggested that glucomannan reduced total cholesterol levels (weighted mean difference [WMD], −19.28 mg/dL; 95% CI, −24.30 to −14.26), LDL cholesterol (WMD, -15.99 mg/dL; 95% CI, −21.31 to −10.67), and triglycerides (WMD, −11.08 mg/dL; 95% CI, −22.07 to 0.09). However, HDL and blood pressure were not affected by glucomannan therapy.21

Glucomannan's cholesterol-lowering effects have been evaluated in children. In a clinical study of 40 children with hypercholesterolemia, patients underwent a 1-week diet run-in phase followed by randomization to either glucomannan 1 to 1.5 g twice daily plus diet or diet alone for 8 weeks. Treatment with glucomannan was associated with a significant reduction in total cholesterol and LDL cholesterol values from baseline compared with the control group. Specifically, significant reductions were noted in favor of women compared with men (total cholesterol: 24% vs 9%, P = 0.004; LDL: 30% vs 9%, P = 0.046).37

The 2017 joint position statement of the Italian Society of Diabetology (ISD) and the Italian Society for the Study of Arteriosclerosis (ISSA) on nutraceuticals for the treatment of hypercholesterolemia strongly recommends the use of fiber (eg, oat beta-glucan, chitosan, glucomannan, guar gum, HPMC, pectin, psyllium) to lower LDL in the general population that fails to increase dietary fiber; in patients with mild hypercholesterolemia and low-to-moderate cardiovascular risk; or in patients with mild hypercholesterolemia and metabolic syndrome (Level I, Strength A).61

Effects on lung cancer

Animal data

A study from China has investigated the ability of konjac powder to inhibit lung cancers in mice.38 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 N-methyl-N′-nitro- N-nitrosoguanidine (MNNG). The study reported no adverse reactions to the konjaku powder.38

Clinical data

Research reveals no clinical data regarding the use of glucomannan for lung cancer.

Atopic disease effects

Animal data

In a model of atopic dermatitis, NC/Nga mice were supplemented with pulverized konjac glucomannan for 8 or 9 weeks. Scratching behaviors and skin severity scores were reduced in those mice fed glucomannan in a dose-dependent fashion. The mice receiving placebo experienced an increase in this behavior. The mice that continued to receive glucomannan experienced an inhibition of eosinophilia and hyperkeratosis.39 Only pulverized konjac glucomannan, not konjac glucomannan, high-viscous konjac glucomannan, or regranulated fine konjac glucomannan, were effective in this model, suggesting that particle size is important. Another study demonstrated that NC/Nga mice fed pulverized konjac glucomannan did not exhibit cervical lymphadenopathy, splenomegaly, or increases in anti–double-stranded DNA, rheumatoid factor immunoglobulin G autoantibodies, or B lymphocyte-activating factor levels.40

Clinical data

Research reveals no clinical data regarding the use of glucomannan for atopic diseases.

Other uses

In a prospective, randomized, placebo-controlled study, 48 newly diagnosed hyperthyroid patients were randomized to receive treatment with methimazole and propranolol plus glucomannan 1.3 g twice daily or placebo for 2 months. At the end of the second, fourth, and sixth weeks, patients receiving glucomannan had significantly lower thyroid hormone levels (ie, T3, T4, FT3, and FT4) compared with those receiving placebo (P < 0.05), with the exception that T3 was not lower with glucomannan treatment compared with placebo at 2 weeks. Hormone levels more rapidly declined in patients receiving glucomannan. Thyroid stimulating hormone levels were suppressed in both groups at weeks 2, 4, and 6; however, it normalized after 8 weeks of treatment in patients receiving glucomannan. At the end of 8 weeks of treatment, these levels were not different between groups. Thus, glucomannan may have a role in the initial treatment of patients with hyperthyroidism to rapidly lower thyroid hormone levels. It is hypothesized that glucomannan's effect on hyperthyroidism may be explained by alterations in enterhepatic circulation, which reduces thyroid hormone levels.41

Dietary administration of konjac glucomannan prevented allergic rhinitis symptoms in mice following immunization and nasal sensitization. Specifically, sneezing was reduced in mice receiving glucomannan compared with controls. Additionally, supplementation with konjac glucomannan reduced total immunoglobulin E concentrations.42

Carboxylated konjac glucomannan has been investigated for its application as a plasma substitute or expander during periods of critical blood and fluid loss. In a rabbit model, the colloid osmostic pressure of a solution containing 1% carboxylated konjac glucomannan was higher than a 6% solution of hydroxyethyl starch and 5% solution of human serum albumin. This allows for a lower dosage of the konjac glucomannan solution to be infused.43

In an in vitro study, the presence of konjac glycomannan hydrosylates was able to inhibit the growth of Cutibacterium acnes.44

Given that konjac glucomannan is degraded in the colon by beta-mannases produced from natural flora and is not degraded in the small intestines, it has gained attention as an excipient for colonic drug delivery.45 Additionally, glucomannan possesses unique biodegradable, solubility, and gelling properties that make it attractive for use as an excipient in tablets, films, beads, micro- and nanoparticles, and hydrogels. Also, glucomannan has been combined with other polysaccharides including carrageenan, xanthan, acetan, gellam gum, alginate, and chitosan to improve gelling properties as part of drug delivery applications.7

Dosing

Clinical studies of glucomannan in diabetes, cholesterol control, and obesity have used doses of 1 to 13 g daily.1, 46, 47, 48, 49 Specifically, 1 to 3 daily has been suggested for weight loss and 3.6 to 13 g daily for type 2 diabetes, insulin-resistance syndrome, and dyslipidemia.1 Dosing in pediatric studies for GI indications was 1.26 g twice daily.56, 57

Pregnancy / Lactation

Information regarding use during pregnancy and lactation is lacking. Until more information is known, use is not recommended in pregnant or breast-feeding women.

Interactions

Given the possibility of reducing blood glucose levels, caution should be used in patients receiving oral hypoglycemic agents, insulin, or alternative medicines that lower glucose levels. Additionally, glucomannan may reduce the bioavailability of other oral medications. Thus, it is recommended to take other medications 1 hour before or 4 hours after glucomannan administration.1

Adverse Reactions

Several cases of severe esophageal obstruction due to glucomannan diet tablets have been reported.50, 51 Seven cases were noted during 1984 and 1985 by the Australian Adverse Drug Reactions Advisory Committee. Four of these obstructions occurred in the proximal one-third of the esophagus. One patient developed mediastinitis due to perforation of the esophagus.52 Thus, patients with conditions of the esophagus or who experience difficulty swallowing in general may be at increased risk of esophageal obstruction associated with glucomannan. Glucomannan-containing tablets have been banned in Australia since May 1985 because these also carry the potential for inducing lower GI 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 patients with diabetes. Therefore, glucomannan should be used with caution by these patients.

A case report described a 31-year-old man who had taken glucomannan capsules for weight loss and subsequently developed short-term cholestatic hepatitis. The patient took 1 to 2 capsules daily 45 days prior to the onset of symptoms. Glucomannan was considered the likely causative agent given the temporal relationship. This suggests a potential hepatotoxic effect may be due to the presence of serotonin.53

"Konjac asthma" is a type of occupational asthma occurring in factories that manufacture konjac flour documented in a 1952 survey. During the production process, "konjac dancing powder" is produced. Inhalation of this powder has led to the development of asthma among workers and nearby residents.54

Minor adverse effects include GI effects such as diarrhea, flatulence, and bloating.1

Toxicology

Glucomannan given to rats at dosages of 500 mg/kg/day for 18 months revealed no toxicity.7, 55 Data suggests minor GI effects (eg, diarrhea, abdominal pain, flatulence) occur with dosages higher than 5 g daily.7

References

Disclaimer

This information relates to an herbal, vitamin, mineral or other dietary supplement. This product has not been reviewed by the FDA to determine whether it is safe or effective and is not subject to the quality standards and safety information collection standards that are applicable to most prescription drugs. This information should not be used to decide whether or not to take this product. This information does not endorse this product as safe, effective, or approved for treating any patient or health condition. This is only a brief summary of general information about this product. It does NOT include all information about the possible uses, directions, warnings, precautions, interactions, adverse effects, or risks that may apply to this product. This information is not specific medical advice and does not replace information you receive from your health care provider. You should talk with your health care provider for complete information about the risks and benefits of using this product.

This product may adversely interact with certain health and medical conditions, other prescription and over-the-counter drugs, foods, or other dietary supplements. This product may be unsafe when used before surgery or other medical procedures. It is important to fully inform your doctor about the herbal, vitamins, mineral or any other supplements you are taking before any kind of surgery or medical procedure. With the exception of certain products that are generally recognized as safe in normal quantities, including use of folic acid and prenatal vitamins during pregnancy, this product has not been sufficiently studied to determine whether it is safe to use during pregnancy or nursing or by persons younger than 2 years of age.

More about glucomannan

1. Keithley J, Swanson B. Glucomannan and obesity: a critical review. Altern Ther Health Med. 2005;11(6):30-34.16320857
2. Kiriyama S, Ichihara Y, Enishi A, Yoshida A. Effect of purification and cellulose treatment on the hypocholesterolemic activity of crude konjac manna. J Nutr. 1972;102(12):1689-1697.4635000
3. Sugiyama N, Shimahara H, inventors; Kabushiki Kaisha Shimizu Manzo Shoten, assignee. Konjac mannan. US patent 3 973 008. August 3, 1976.
4. 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.
5. Chua M, Baldwin TC, Hocking TJ, Chan K. Traditional uses and potential health benefits of Amorphophallus konjac K. Koch ex N.E.Br. J Ethnopharmacol. 2010;128(2):268-278.20079822
6. Vanderbeek PB, Fasano C, O'Malley G, Hornstein J. Esophageal obstruction from a hygroscopic pharmacobezoar containing glucomannan. Clin Toxicol (Phila). 2007;45(1):80-82.17357389
7. Alonso-Sande M, Teijeiro-Osorio D, Remuñán-López C, Alonso MJ. Glucomannan, a promising polysaccharide for biopharmaceutical purposes. Eur J Pharm Biopharm. 2009;72(2):453-462.18511246
8. Chen HL, Fan YH, Chen ME, Chan Y. Unhydrolyzed and hydrolyzed konjac glucomannans modulated cecal and fecal microflora in Balb/c mice. Nutrition. 2005;21(10):1059-1064.16157244
9. Fujiwara S, Hirota T, Nakazato H, Muzutani T, Mitsuoka T. Effect of konjac mannan on intestinal microbial metabolism in mice bearing human flora and in conventional F344 mice. Food Chem Toxicol. 1991;29(9):601-606.1657742
10. Elamir AA, Tester RF, Al-Ghazzewi FH, et al. Effects of konjac glucomannan hydrolysates on the gut microflora of mice. Nutr Food Sci. 2008;38(5):422-429.
11. Chen HL, Cheng HC, Liu YJ, Liu SY, Wu WT. Konjac acts as a natural laxative by increasing stool bulk and improving colonic ecology in healthy adults. Nutrition. 2006;22(11-12):1112-1119.17027233
12. Chen HL, Cheng HC, Wu WT, Liu YJ, Liu SY. Supplementation of konjac glucomannan into a low-fiber Chinese diet promoted bowel movement and improved colonic ecology in constipated adults: a placebo-controlled, diet-controlled trial. J Am Coll Nutr. 2008;27(1):102-108.18460488
13. Loening-Baucke V, Miele E, Staiano A. Fiber (glucomannan) is beneficial in the treatment of childhood constipation. Pediatrics. 2004;113(3, pt 1):e259-e264.14993586
14. Jenkins DJ, Wolever TM, Leeds AR, et al. Dietary fibres, fibre analogues, and glucose tolerance: importance of viscosity. Br Med J. 1978;1(6124):1392-1394.647304
15. Vuksan V, Sievenpiper JL, Xu Z, et al. Konjac-Mannan and American ginsing: emerging alternative therapies for type 2 diabetes mellitus. J Am Coll Nutr. 2001;20(suppl 5):370S-380S.11603646
16. Lu XJ, Chen XM, Fu DX, Cong W, Ouyang F. Effect of Amorphophallus konjac oligosaccharides on STZ-induced diabetes model of isolated islets. Life Sci. 2002;72(6):711-719.12467911
17. Guar gum, dietary fiber and diabetes. Med Lett Drugs Ther. 1979;21(12):51-52.449840
18. Doi K, Matsuura M, Kawara A, Baba S. Treatment of diabetes with glucomannan (konjac mannan). Lancet. 1979;1(8123):987-988.87668
19. Huang CY, Zhang MY, Peng SS, et al. Effect of Konjac food on blood glucose level in patients with diabetes. Biomed Environ Sci. 1990;3(2):123-131.1966003
20. Chearskul S, Kriengsinyos W, Kooptiwut S, et al. Immediate and long-term effects of glucomannan on total ghrelin and leptin in type 2 diabetes mellitus. Diabetes Res Clin Pract. 2009;83(2):e40-e42.19108925
21. Sood N, Baker WL, Coleman CI. Effect of glucomannan on plasma lipid and glucose concentrations, body weight, and blood pressure: systematic review and meta-analysis. Am J Clin Nutr. 2008;88(4):1167-1175.18842808
22. Reffo GC, Ghirardi PE, Forattini C. Double-blind evaluation of glucomannan versus placebo in postinfarcted patients after cardiac rehabilitation. Curr Ther Res Clin Exp. 1990;47(5):753-758.
23. Kraemer WJ, Vingren JL, Silvestre R, et al. Effect of adding exercise to a diet containing glucomannan. Metabolism. 2007;56(8):1149-1158.17618964
24. Vido L, Facchin P, Antonello I, Gobber D, Rigon F. Childhood obesity treatment: double blinded trial on dietary fibres (glucomannan) versus placebo. Padiatr Padol. 1993;28(5):133-136.8247594
25. Rogovik AL, Chanoine JP, Goldman RD. Pharmacotherapy and weight-loss supplements for treatment of paediatric obesity. Drugs. 2010;70(3):335-346.20166770
26. Livieri C, Novazi F, Lorini R. The use of highly purified glucomannan-based fibers in childhood obesity [in Italian]. Pediatr Med Chir. 1992;14(2):195-198.1324483
27. Lyon MR, Reichert RG. The effect of a novel viscous polysaccharide along with lifestyle changes on short-term weight loss and associated risk factors in overweight and obese adults: an observational retrospective clinical program analysis. Altern Med Rev. 2010;15(1):68-75.20359270
28. Kiriyama S, Enishi A, Yura K. Inhibitory effect of konjac mannan on bile acid transport in the everted sacs from rat ileum. J Nutr. 1974;104(1):69-78.4809066
29. McCarty MF. Glucomannan minimizes the postprandial insulin surge: a potential adjuvant for hepatothermic therapy. Med Hypotheses. 2002;58(6):487-490.12323114
30. Kiriyama S, Okazaki Y, Yoshida A. Hypocholesterolemic effect of polysaccharides and polysaccharide-rich foodstuffs in cholesterol-fed rats. J Nutr. 1969;97(3):382-388.5773340
31. Ikegami S, Harada H, Tshuchihashi N, Nagayama S, Nishide E, Innami S. Effect of indigestible polysaccharides on pancreatic exocrine secretion and biliary output. J Nutr Sci Vitaminol (Tokyo). 1984;30(6):515-523.6085345
32. Arvill A, Bodin L. Effect of short-term ingestion of konjac glucomannan on serum cholesterol in healthy men. Am J Clin Nutr. 1995;61(3):585-589.7872224
33. Zhang MY, Huang CY, Wang X, Hong JR, Peng SS. The effect of foods containing refined Konjac meal on human lipid metabolism. Biomed Environ Sci. 1990;3(1):99-105.21587494
34. Hou YH, Zhang LS, Zhou HM, Wang RS, Zhang YZ. Influences of refined konjac meal on the levels of tissue lipids and the absorption of four minerals in rats. Biomed Environ Sci. 1990;3(3):306-314.2252550
35. Shimizu H, Yamauchi M, Kuramoto T, Kubota N, Matsuda M, Hoshita T. Effects of dietary konjac mannan on serum and liver cholesterol levels and biliary bile acid composition in hamsters. J Pharmacobiodyn. 1991;14(7):371-375.1666411
36. Wood RJ, Fernandez ML, Sharman MJ, et al. Effects of a carbohydrate-restricted diet with and without supplemental soluble fiber on plasma low-density lipoprotein cholesterol and other clinical markers of cardiovascular risk. Metabolism. 2007;56(1):58-67.17161227
37. Martino F, Martino E, Morrone F, Carnevali E, Forcone R, Niglio T. Effect of dietary supplementation with glucomannan on plasma total cholesterol and low density lipoprotein cholesterol in hypercholesterolemic children. Nutr Metab Cardiovasc Dis. 2005;15(3):174-180.15955465
38. Luo DY. Inhibitory effect of refined Amorphophallus konjac on MNNG-induced lung cancers in mice [in Chinese]. Zhonghua Zhong Liu Za Zhi. 1992;14(1):48-50.1327690
39. Onishi N, Kawamoto S, Suzuki H, et al. Dietary pulverized konjac glucomannan suppresses scratching behavior and skin inflammatory immune responses in NC/Nga mice. Int Arch Allergy Immunol. 2007;144(2):95-104.17536217
40. Onishi N, Kawamoto S, Suzuki H, Hide M, Ono K. Development of autoantibody responses in NC/Nga mice: its prevention by pulverized konjac glucomannan feeding. Arch Dermatol Res. 2008;300(2):95-99.17938942
41. Azezli AD, Bayraktaroglu T, Orhan Y. The use of konjac glucomannan to lower serum thyroid hormones in hyperthyroidism. J Am Coll Nutr. 2007;26(6):663-668.18187431
42. Onishi N, Kawamoto S, Ueda K, et al. Dietary pulverized konjac glucomannan prevents the development of allergic rhinitis-like symptoms and IgE response in mice. Biosci Biotechnol Biochem. 2007;71(10):2551-2556.17928709
43. Li S, Hu T, Chen Y, et al. Chemically modified konjac glucomannan with high colloid osmotic pressure: physiological evaluation in a rabbit model as a plasma substitute. Glycobiology. 2010;20(8):950-958.20466646
44. Al-Ghazzewi FH, Tester RF. Effect of konjac glucomannan hydrolysates and probiotics on the growth of the skin bacterium Propionibacterium acnes in vitro. Int J Cosmet Sci. 2010:32(2):139-142.19818083
45. Alvarez-Manceñido F, Landin M, Martínez-Pacheco R. Konjac glucomannan/xanthan gum enzyme sensitive binary mixtures for colonic drug delivery. Eur J Pharm Biopharm. 2008;69(2):573-581.18294827
46. 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(1):36-42.12569112
47. 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(1):9-14.1857960
48. Marsicano LJ, Berrizbeitia ML, Mondelo A. Use of glucomannan dietary fiber in changes in intestinal habit [in Spanish]. G E N. 1995;49(1):7-14.8566676
49. Walsh DE, Yaghoubian V, Behforooz A. Effect of glucomannan on obese patients: a clinical study. Int J Obes. 1984;8(4):289-293.6096282
50. Fung M. Glucomanna diet tablets. Med J Aust. 1984;140(6):350.6321923
51. Gaudry P. Glucomanna diet tablets. Med J Aust. 1985;142(3):204.3855252
52. Henry DA, Mitchell AS, Aylward J, Fung MT, McEwen J, Rohan A. Glucomannan and risk of oesophageal obstruction. Br Med J (Clin Res Ed). 1986;292(6520):591-92.3004635
53. Villaverde AF, Benlloch S, Berenguer M, Rayón JM, Pina R, Berenguer J. Acute hepatitis of cholestatic type possibly associated with the use of glucomannan (Amorphophalus konjac). J Hepatol. 2004;41(6):1061-1062.15582144
54. Bernstein JA, Crandall MS, Floyd R. Respiratory sensitization of a food manufacturing worker to konjac glucomannan. J Asthma. 2007;44(8):675-680.17943580
55. Peng SS, Zhang MY, Zhang YZ, Wu ZH. Long-term animal feeding trial of the refined konjac meal. II. Effects of the refined konjac meal on the aging of the brain, liver, and cardiovascular tissue cells in rats. Biomed Environ Sci. 1995;8(1):80-87.7605604
56. Horvath A, Dziechciarz P, Szajewska H. Glucomannan for abdominal pain-related functional gastrointestinal disorders in children: a randomized trial. World J Gastroenterol. 2013;19(20):3062-3068.23716985
57. Chmielewska A, Horvath A, Dziechciarz P, Szajewska H. Glucomannan is not effective for the treatment of functional constipation in children: a double-blind, placebo-controlled, randomized trial. Clin Nutr. 2011;30(4):462-468.21320737
58. Martino F, Puddu PE, Pannarale G, et al. Low dose chromium-polynicotinate or policosanol is effective in hypercholesterolemic children only in combination with glucomannan. Atherosclerosis. 2013;228(1):198-202.23453352
59. Onakpoya I, Posadzki P, Ernst E. The efficacy of glucomannan supplementation in overweight and obesity: a systematic review and meta-analysis of randomized clinical trials. J Am Coll Nutr. 2014;33(1):70-78.24533610
60. Keithyley JK, Swanson B, Mikolaitis SL, et al. Safety and efficacy of glucomannan for weight loss in overweight and moderately obese adults. J Obesity. 2013;2013:610908.24490058
61. Pirro M, Vetrani C, Bianchi C, Mannarino MR, Bernini F, Rivellese AA. Joint position statement on "Nutraceuticals for the treatment of hypercholesterolemia" of the Italian Society of Diabetology (SID) and of the Italian Society for the Study of Arteriosclerosis (SISA). Nutr Metab Cardiovasc Dis. 2017;27(1):2-17.27956024

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