Home Ingredients Glucomannan (Konjac Root Fiber)
Weight ManagementMetabolic HealthCardiovascularGut Health

Glucomannan (Konjac Root Fiber)

Amorphophallus konjac
Evidence Level
Strong
2 Clinical Trials
4 Documented Benefits
4/5 Evidence Score

Glucomannan is a water-soluble dietary fiber from the root of the konjac plant (Amorphophallus konjac). It holds a large amount of water, forms a highly viscous gel and can swell to many times its original size, which is why it must be taken with plenty of water. Studied doses are about 3 to 4 g a day. Its best-supported effect is on cholesterol: several meta-analyses agree that it lowers total and LDL cholesterol. Under Regulation (EU) No 432/2012 the European Commission has authorised two claims: 4 g/day contributes to maintaining normal blood cholesterol, and 3 g/day taken before meals with 1 to 2 glasses of water contributes to weight loss within an energy-restricted diet. In the US, glucomannan is not among the fibers in the FDA's soluble fiber heart health claim. Weight-loss results are small and inconsistent, with one meta-analysis positive and another finding no significant effect.

Studied Dose About 3 g/day in the LDL meta-analysis. EU claims: 4 g/day for cholesterol, and 3 g/day as 1 g three times daily before meals with 1 to 2 glasses of water for weight loss within an energy-restricted diet. Always take with plenty of water.
Active Compound Konjac glucomannan (KGM), a highly viscous soluble polysaccharide made of mannose and glucose units

Benefits

Supports healthy LDL cholesterol levels

Several meta-analyses agree that glucomannan lowers total and LDL cholesterol. In a meta-analysis of 12 randomized trials (370 people), about 3 g/day lowered LDL by 0.35 mmol/L (about 10%) and non-HDL cholesterol by about 7%, with no change in apolipoprotein B. The most recent pooled analysis called the change too small to matter clinically on its own. The EU authorises a cholesterol claim at 4 g/day.

Supported by Trial 2, Trial 1

Body weight within an energy-restricted diet

Results are small and inconsistent. One meta-analysis of 14 trials found 0.79 kg more weight loss than control; another, limited to 8 trials in overweight or obese participants, found no significant difference. Placebo-controlled trials in 53 adults (8 weeks) and 96 children (12 weeks) found no effect on weight or BMI. The EU claim applies to 3 g/day within an energy-restricted diet.

Supported by Trial 1, Trial 2

Fasting and post-meal blood sugar

A meta-analysis of 14 trials found fasting glucose about 7.4 mg/dL lower than control, although people with impaired glucose metabolism benefited less. In 6 trials of 440 people with type 2 diabetes, fasting and 2-hour post-meal glucose were lower. In 53 overweight adults, 4 g/day for 8 weeks changed no glucose value. This is more limited evidence than for cholesterol.

Supported by Trial 1, Trial 2

Bowel regularity and gut bacteria

In 7 constipated adults on a controlled low-fiber diet, 1.5 g three times daily raised weekly bowel movements from 4.1 to 5.3 and increased fecal lactobacilli and short-chain fatty acids. In 3 trials of 122 constipated children it added about 1.4 bowel movements a week but did not change stool consistency. In elite male athletes with constipation it improved symptom scores versus placebo.

Supported by Trial 1, Trial 2

Mechanism of action

1

Gel viscosity and water holding

Glucomannan holds a great deal of water, forms highly viscous solutions and expands rapidly to many times its original size. This viscosity is thought to underlie its effects on blood lipids and on how quickly food moves through the gut. Fullness is often assumed to follow, but in a placebo-controlled trial that rated hunger and fullness, 4 g/day for 8 weeks changed neither.

2

Bile acid binding and cholesterol

Viscous fibers are proposed to trap bile acids in the small intestine so fewer are reabsorbed. The liver then uses cholesterol to make new bile acids, which lowers LDL in the blood. For glucomannan this step is inferred from its viscosity: the trials cited here measured blood lipids, not bile acids.

3

Gut hormones: proposed, with thin human data

Viscous fibers are proposed to influence gut hormones involved in appetite, such as GLP-1 and ghrelin. Human data for glucomannan are sparse. In an uncontrolled 12-week study of konjac foods in 26 people with type 2 diabetes, GLP-1 only tended to rise (p = 0.071). A small study in type 2 diabetes reported that glucomannan taken before a glucose drink enhanced the fall in ghrelin.

Clinical trials

1
Glucomannan and Lipids, Glucose and Body Weight: Meta-Analysis of 14 Trials
PubMed

Systematic review and meta-analysis of 14 randomized controlled trials. (Sood et al. 2008, Am J Clin Nutr)

531 participants pooled from 14 randomized trials.

Glucomannan lowered total cholesterol by 19.3 mg/dL, LDL cholesterol by 16.0 mg/dL, triglycerides by 11.1 mg/dL, body weight by 0.79 kg (95% CI 0.05 to 1.53 kg) and fasting glucose by 7.4 mg/dL versus control. HDL cholesterol and blood pressure did not change. Children, people already on dietary changes, and people with impaired glucose metabolism did not benefit to the same degree. A later meta-analysis of 8 trials in overweight or obese participants found no significant weight difference.

2
Konjac Glucomannan and LDL Cholesterol: Meta-Analysis of 12 Trials
PubMed

Systematic review and meta-analysis of 12 randomized controlled trials lasting at least 3 weeks. (Ho et al. 2017, Am J Clin Nutr)

370 participants pooled from 12 randomized trials, 8 in adults and 4 in children.

About 3 g/day of konjac glucomannan lowered LDL cholesterol by 0.35 mmol/L (95% CI 0.25 to 0.46), roughly 10%, and non-HDL cholesterol by 0.32 mmol/L, about 7%, versus control. Data from 6 trials showed no effect on apolipoprotein B.

Side effects and drug interactions

Common Potential side effects

Choking and blockage is the main risk with this ingredient. Glucomannan swells rapidly on contact with water and can lodge in the throat or esophagus. Take every dose with at least 250 mL (8 oz) of water, sitting upright, and not just before lying down or at bedtime. Do not use tablet forms: Australia permanently bans glucomannan in tablet form (Consumer Protection Notice F2010L03293) because a tablet can expand on contact with saliva and block the throat before it reaches the stomach; capsules and powders are not covered by the ban. Anyone with difficulty swallowing, a known narrowing of the esophagus, or a history of bowel obstruction should not take glucomannan in any form
Abdominal discomfort, gas and bloating, especially at first; start with a lower dose and increase gradually
Diarrhea or constipation, both reported as adverse events in weight-loss trials
Esophageal obstruction has been reported, including a published case of a 37-year-old woman who developed delayed esophageal obstruction after taking an over-the-counter glucomannan diet aid and was later found to have an esophageal web. Under Regulation (EU) No 432/2012, products carrying glucomannan claims must warn people with swallowing difficulties, or anyone taking it with too little fluid, about choking

Important Drug interactions

Other oral medicines: glucomannan may change how well other medicines are absorbed; take them at a different time of day and ask your pharmacist about spacing
Diabetes medicines: glucomannan lowers fasting glucose a little at most, but if you use insulin or a sulfonylurea, monitor your blood sugar, since any added glucose lowering can push you into hypoglycemia
Cholesterol-lowering medicines: effects on LDL may add together; recheck your lipid panel with your doctor

Featured in these supplement guides

Blood Sugar Control→Constipation→Weight Loss→

More Weight Management Ingredients

Weight Management
Clarinol® (Conjugated Linoleic Acid — Stepan Lipid Nutrition)
Clarinol® is a branded conjugated linoleic acid (CLA), a fatty acid derived from safflower…
Weight Management
NEOBEE® (Medium-Chain Triglycerides — Stepan)
NEOBEE® is a line of medium-chain triglycerides (MCTs) from Stepan. MCTs are fats built fr…
Weight Management
CGA-7™ (Green Coffee Chlorogenic Acid Complex — Vidya Herbs)
CGA-7 is a decaffeinated green (unroasted) coffee bean extract from Vidya Herbs, standardi…
Weight Management
White Kidney Bean Extract (Phaseolus vulgaris)
White kidney bean extract is a water extract of the common white kidney bean (Phaseolus vu…

Explore Other Ingredients

Metabolic Health
Berberine
Berberine is a yellow compound from plants such as barberry, goldenseal and Chinese goldth…
Metabolic Health
GlucoVantage® (Dihydroberberine)
GlucoVantage® is NNB Nutrition's branded dihydroberberine (DHB), a reduced form of berberi…
Metabolic Health
Inositol (Myo-Inositol)
Inositol is a sugar-like compound that the body makes from glucose and that takes part in…

Related articles from our blog

📝 Article
Synbiotics for Skin: What a 2026 Wrinkle Study Found
"Beauty from within" has become one of the biggest ideas in supplements, and the science behind it, the gut-skin axis, i…
July 15, 2026
📝 Article
Do Fat Burners Actually Work?
No category of supplement promises more and delivers less than the fat burner. The bottles show flames and shredded abs,…
June 21, 2026

Frequently asked questions about Glucomannan (Konjac Root Fiber)

How much glucomannan should I take?

The EU weight-loss claim is based on 1 gram three times daily (3 grams total) before meals, each with 1 to 2 glasses of water, within an energy-restricted diet; the EU cholesterol claim is based on 4 grams a day. Always take it with plenty of liquid.

What is glucomannan used for?

Glucomannan is a highly absorbent soluble fiber from konjac root, used mainly for cholesterol support, with weaker and much less consistent evidence for weight management, plus digestive regularity. It does expand in the stomach, but in a placebo-controlled trial that rated hunger and fullness it changed neither.

How do I take glucomannan safely?

Always take it with a full glass of water and never dry, because it swells to many times its size on contact with water and can cause choking or blockage in the throat or esophagus. Stay upright afterwards and do not take it just before bed. Avoid tablet forms, which Australia bans for this reason. Take other medicines at a different time, since it may affect their absorption.

Does glucomannan have side effects?

The most common effects are gas, bloating, and loose stools, which often ease over time. The main safety concern is choking or blockage when it is taken with too little water. Anyone with difficulty swallowing or a narrowed esophagus should not take glucomannan in any form, and nobody should take it as a tablet or lie down straight after a dose.

What is Glucomannan?

Glucomannan is a water-soluble dietary fiber from the root of the konjac plant (Amorphophallus konjac). It holds a large amount of water, forms a highly viscous gel and can swell to many times its original size, which is why it must be taken with plenty of water. Studied doses are about 3 to 4 g a day.

Does Glucomannan interact with any medications?

Possible interactions include: Other oral medicines: glucomannan may change how well other medicines are absorbed; take them at a different time of day and ask your pharmacist about spacing Diabetes medicines: glucomannan lowers fasting glucose a little at most, but if you use insulin or a sulfonylurea, monito… If you take prescription medication, check with a pharmacist or doctor before using it.

How strong is the scientific evidence for Glucomannan?

NutraSmarts rates the evidence for Glucomannan as Strong (4 out of 5). It is backed by 2 study summaries and 16 cited references summarized on this page. A higher rating reflects more, larger, and better-designed human studies.

References(16 citations)

Evidence ratings on NutraSmarts are based on the totality of human clinical research, with emphasis on randomized controlled trials, meta-analyses, and systematic reviews. The references below directly support claims made throughout this page.

  1. 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):1167-75. doi: 10.1093/ajcn/88.4.1167.PubMedUsed to support: Meta-analysis of 14 randomized trials (531 participants). Glucomannan lowered total cholesterol by 19.3 mg/dL, LDL cholesterol by 16.0 mg/dL, triglycerides by 11.1 mg/dL and fasting glucose by 7.4 mg/dL versus control. Body weight fell by 0.79 kg, but the confidence interval ran from 1.53 kg down to 0.05 kg, so the weight result sat close to zero. HDL cholesterol and blood pressure did not change, and the authors reported that children, people already modifying their diet, and people with impaired glucose metabolism did not benefit to the same degree.
  2. Ho HVT, Jovanovski E, Zurbau A, Blanco Mejia S, Sievenpiper JL, Au-Yeung F, Jenkins AL, Duvnjak L, Leiter L, Vuksan V. A systematic review and meta-analysis of randomized controlled trials of the effect of konjac glucomannan, a viscous soluble fiber, on LDL cholesterol and the new lipid targets non-HDL cholesterol and apolipoprotein B. Am J Clin Nutr. 2017;105(5):1239-1247. doi: 10.3945/ajcn.116.142158.PubMedUsed to support: Meta-analysis of 12 randomized trials (370 participants, 8 trials in adults and 4 in children). About 3 g/day of konjac glucomannan lowered LDL cholesterol by 0.35 mmol/L, roughly 10 percent, and non-HDL cholesterol by 0.32 mmol/L, about 7 percent, versus control; 6 trials with apolipoprotein B data showed no effect on it.
  3. Keithley JK, Swanson B, Mikolaitis SL, DeMeo M, Zeller JM, Fogg L, Adamji J. Safety and efficacy of glucomannan for weight loss in overweight and moderately obese adults. J Obes. 2013;2013:610908. doi: 10.1155/2013/610908.PubMedUsed to support: Randomized, double-blind, placebo-controlled trial in 53 overweight and moderately obese adults aged 18 to 65. Participants took 1.33 g of glucomannan or placebo capsules with 8 oz of water one hour before each of three meals for 8 weeks. Weight change did not differ between groups, and there was no difference in body composition, rated hunger and fullness, or lipid and glucose values. The supplement was well tolerated, with no change in liver enzymes or creatinine.
  4. Vuksan V, Sievenpiper JL, Owen R, Swilley JA, Spadafora P, Jenkins DJ, Vidgen E, Brighenti F, Josse RG, Leiter LA, Xu Z, Novokmet R. 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. doi: 10.2337/diacare.23.1.9.PubMedUsed to support: Crossover metabolic feeding trial in 11 adults with insulin resistance syndrome, comparing konjac-mannan biscuits (8 to 13 g glucomannan per day) with wheat-bran biscuits over two 3-week periods. Total cholesterol fell 12.4 percent, LDL cholesterol 22 percent, apolipoprotein B 15.1 percent and serum fructosamine 5.2 percent versus wheat bran. Fasting glucose, insulin, triglycerides, HDL cholesterol and body weight did not change. Small, with a wheat-bran comparator and a food dose several times a typical supplement serving.
  5. 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):70-8. doi: 10.1080/07315724.2014.870013.PubMedUsed to support: Systematic review: 18 trials identified, 9 included. Pooling 8 randomized trials in overweight or obese participants gave a mean weight difference of 0.22 kg versus placebo (95 percent CI 0.62 kg lower to 0.19 kg higher), not statistically significant, with substantial heterogeneity. Reported adverse events were abdominal discomfort, diarrhea and constipation.
  6. Zalewski BM, Szajewska H. No Effect of Glucomannan on Body Weight Reduction in Children and Adolescents with Overweight and Obesity: A Randomized Controlled Trial. J Pediatr. 2019;211:85-91.e1. doi: 10.1016/j.jpeds.2019.03.044.PubMedUsed to support: A randomized, double-blind, placebo-controlled trial in 96 children and adolescents aged 6 to 17 with overweight or obesity, given 3 g/day of glucomannan or maltodextrin placebo for 12 weeks alongside dietary and lifestyle advice, then followed a further 12 weeks. Glucomannan had no effect on BMI-for-age z score at 12 weeks (mean difference 0.0, 95 percent CI 0.1 lower to 0.1 higher). Total and LDL cholesterol were lower in the glucomannan group at 12 weeks. Blood pressure was higher in the glucomannan group at 12 weeks (systolic) and 24 weeks (diastolic). Adverse events did not differ between groups.
  7. 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):102-8. doi: 10.1080/07315724.2008.10719681.PubMedUsed to support: Diet-controlled study in 7 constipated adults: a 21-day placebo period, then 1.5 g konjac glucomannan three times daily for 21 days. Weekly bowel movements rose from 4.1 to 5.3. Fecal wet weight and moisture did not change; dry fecal weight rose. Fecal lactobacilli and the daily output of bifidobacteria, lactobacilli and total bacteria increased, fecal acetate, propionate and isobutyrate rose, and fecal pH fell. A sequential design in 7 people, not a randomized parallel trial.
  8. Han Y, Zhang L, Liu XQ, Zhao ZJ, Lv LX. Effect of glucomannan on functional constipation in children: a systematic review and meta-analysis of randomised controlled trials. Asia Pac J Clin Nutr. 2017;26(3):471-477. doi: 10.6133/apjcn.032016.03.PubMedUsed to support: Meta-analysis of 3 randomized trials in 122 children with functional constipation. Glucomannan increased defecation frequency by 1.40 bowel movements per week (95 percent CI 0.36 to 2.44). It did not significantly change stool consistency (standardised mean difference 0.48, 95 percent CI 0.44 lower to 1.40 higher) or, across the 2 trials reporting it, the rate of successful treatment (risk ratio 1.36, 95 percent CI 0.48 to 3.81). The authors caution that the samples are small and that the risks of glucomannan products need to be considered. Note the population: children, not adults.
  9. Zhu Y, Chen X, Song G. Effects of konjac glucomannan on gastrointestinal symptoms and gut microbiota in athletes with functional constipation: a double-blind randomized controlled trial. Eur J Nutr. 2025;64(8):303. doi: 10.1007/s00394-025-03826-3.PubMedUsed to support: A double-blind, placebo-controlled randomized trial of 8 weeks of konjac glucomannan in male elite Taekwondo athletes with functional constipation diagnosed by Rome IV criteria. Compared with placebo, the glucomannan group improved on the Patient Assessment of Constipation Symptoms and Quality of Life scores, bowel movement frequency and the Bowel Function Index. Stool sequencing showed greater microbial alpha-diversity and higher relative abundance of Prevotella_9, Phascolarctobacterium, Lactobacillus and Bacteroides, with lower Alistipes and Desulfovibrio. The population is narrow: male elite athletes in hard training, not general adult users.
  10. Vanderbeek PB, Fasano C, O'Malley G, Hornstein J. Esophageal obstruction from a hygroscopic pharmacobezoar containing glucomannan. Clin Toxicol (Phila). 2007;45(1):80-2. doi: 10.1080/15563650601006215.PubMedUsed to support: Case report. A 37-year-old woman developed delayed esophageal obstruction after taking an over-the-counter glucomannan diet aid; it cleared after forceful vomiting just before planned endoscopy, and later endoscopy found an esophageal web. The authors note that glucomannan forms highly viscous solutions and expands rapidly to many times its original size, and warn about hygroscopic products in people with existing upper digestive tract problems.
  11. Zhang Z, Zhang Y, Tao X, Wang Y, Rao B, Shi H. Effects of Glucomannan Supplementation on Type II Diabetes Mellitus in Humans: A Meta-Analysis. Nutrients. 2023;15(3):601. doi: 10.3390/nu15030601.PubMedUsed to support: Meta-analysis of 6 randomized trials in 440 people with type 2 diabetes. Glucomannan lowered total cholesterol, LDL, fasting glucose, 2-hour post-meal glucose, fasting insulin and serum fructosamine versus control. A population with type 2 diabetes, not healthy adults.
  12. Haijun Z, Ke Z, Dawei Z, Haedi AR, Poorasadollah E, Cheng C. Does glucomannan supplementation exert profitable effects on serum lipid profile in adults? A systematic review and meta-analysis. Prostaglandins Other Lipid Mediat. 2025;176:106934. doi: 10.1016/j.prostaglandins.2024.106934.PubMedUsed to support: Meta-analysis in adults. Glucomannan significantly lowered total and LDL cholesterol but did not change HDL or triglycerides. The authors state the decreases are not clinically important and that glucomannan can be considered only an adjunct in managing blood lipids.
  13. Ueno H, Haraguchi N, Azuma M, Shiiya T, Noda T, Ebihara E, Uehira Y, Uchida T, Sasaba K, Nakamura M, Uchimura N, Kita E, Umemura A, Nobe T, Sumoto E, Yano Y, Nakazato M. Active Consumption of Konjac and Konjac Products Improves Blood Glucose Control in Patients with Type 2 Diabetes Mellitus. J Am Nutr Assoc. 2023;42(2):123-129. doi: 10.1080/07315724.2021.2002739.PubMedUsed to support: Uncontrolled 12-week study in 26 Japanese people with type 2 diabetes asked to eat konjac foods at least once a day. HbA1c and fasting glucose fell, body weight did not change, and plasma GLP-1 only tended to rise (p = 0.071). Konjac foods, not a glucomannan supplement, and no control group.
  14. Chearskul S, Kriengsinyos W, Kooptiwut S, Sangurai S, Onreabroi S, Churintaraphan M, Semprasert N, Nitiyanant W. Immediate and long-term effects of glucomannan on total ghrelin and leptin in type 2 diabetes mellitus. Diabetes Res Clin Pract. 2009;83(2):e40-2. doi: 10.1016/j.diabres.2008.11.014.PubMedUsed to support: Short report in people with type 2 diabetes. Glucomannan given before a glucose load enhanced the fall in ghrelin, and 4 weeks of use blunted the rise in fasting ghrelin.
  15. European Commission. Commission Regulation (EU) No 432/2012 of 16 May 2012 establishing a list of permitted health claims made on foods, other than those referring to the reduction of disease risk and to children's development and health. Official Journal of the European Union. 2012;OJ L 136, 25.5.2012, p. 1..SourceUsed to support: Not PubMed-indexed; EU regulation. Lists two glucomannan claims: it contributes to maintaining normal blood cholesterol at 4 g/day, and in an energy-restricted diet it contributes to weight loss at 3 g/day taken as three 1 g doses with 1 to 2 glasses of water before meals. Both require a choking warning for people with swallowing difficulties or taking it with inadequate fluid.
  16. Australian Competition and Consumer Commission. Glucomannan in tablet form. Product Safety Australia. 2010;Federal Register of Legislation F2010L03293..SourceUsed to support: Not PubMed-indexed; official product safety notice. Glucomannan in tablet form is permanently banned in Australia because a tablet can expand on contact with saliva before reaching the stomach and block the throat, causing choking, internal injury or suffocation. Capsule and powder forms are not banned.