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Research · Supplements

Glucomannan

Two meta-analyses found LDL cholesterol lower, by 16 mg/dL in one and about 10% at 3 g a day in the other. Weight results disagree, from 0.79 kg more loss to no significant difference. Children lost no extra weight. Case reports describe esophageal obstruction from tablets, and konjac jelly candies were linked to choking deaths.

Add to Bio HackChecked 2026-11-09
Status
Dietary supplement in the US. FDA warned in 2001 about choking on konjac candy after several deaths, and Import Alert 33-15 allows detention of firm mini-cup jelly candies.
Also called
konjac, konjac glucomannan, KGM, konjac root, konjac-mannan, Amorphophallus konjac, elephant yam, shirataki fiber
Taken for
weight loss, appetite, fullness, cholesterol, blood sugar, constipation

Strong several reviews agree · Moderate one review or consistent trials · Limited one or a few small studies · Untested no study in people, listed with what it rests on

Shown to help3

Reported risks4

What people take it for, and what was found

Shown to help3

Strong

LDL cholesterol

Shown to lower LDL cholesterol by about 10%, about 16 mg/dL, in adults and children. Changes were not significant in adults with insulin resistance.

The numbers and sources
Effect
Across 14 studies with 531 participants, glucomannan lowered total cholesterol 19.28 mg/dL (95% CI -24.30 to -14.26), LDL 15.99 mg/dL (95% CI -21.31 to -10.67) and triglycerides 11.08 mg/dL (95% CI -22.07 to -0.09), with no change in HDL [1]. Across 12 studies with 370 participants, LDL fell 0.35 mmol/L (95% CI -0.46 to -0.25) and non-HDL cholesterol 0.32 mmol/L, about 10% and 7%. Apolipoprotein B did not change in 6 trials [2].
Population
Adults and children in RCTs [1][2].
Sources
[1], [2]
Caveats
Trials were small and short, with follow-up of at least 3 weeks in [2]. In 11 trials restricted to adults with insulin resistance-related conditions, lipid changes were not significant overall, with LDL and total cholesterol lower only in subgroups above 3,000 mg a day or at 4 weeks or less [3].
Moderate

Fasting blood sugar

Shown to lower fasting glucose about 7 mg/dL in adults. In insulin resistance, the result lost significance under another analysis.

The numbers and sources
Effect
Fasting blood glucose was 7.44 mg/dL lower with glucomannan (95% CI -14.16 to -0.72). People with impaired glucose metabolism did not benefit to the same degree [1]. In 11 trials in adults with insulin resistance-related conditions, fasting glucose was 7.02 mg/dL lower (95% CI -13.56 to -0.49) [3].
Population
14 studies with 531 participants [1]. Adults with insulin resistance-related conditions in 11 trials [3].
Sources
[1], [3]
Caveats
The two reviews studied different populations. The result in [3] lost statistical significance under an alternative correlation assumption, and its authors call for more high-quality trials.
LimitedStudied in men

Constipation

One trial found better constipation scores and more frequent bowel movements on konjac glucomannan in male Taekwondo athletes with functional constipation.

The numbers and sources
Effect
In one 8-week double-blind trial, konjac glucomannan improved constipation symptom scores, constipation quality of life, bowel movement frequency and bowel function scores against placebo (p < 0.05 for all) [8].
Population
Elite male Taekwondo athletes with functional constipation by Rome IV criteria, in China [8].
Sources
[8]
Caveats
One trial. The abstract does not give the number enrolled, the dose or effect sizes [8].

Mixed results1

Moderate

Weight loss

Mixed results: one review found about 0.8 kg more weight loss, and a review of overweight and obese adults found no significant difference.

The numbers and sources
Effect
In the 2008 meta-analysis, body weight was 0.79 kg lower with glucomannan (95% CI -1.53 to -0.05) [1]. A 2014 meta-analysis of 8 RCTs restricted to overweight and obese participants found a difference of 0.22 kg that was not significant (95% CI -0.62 to 0.19, I² 65%) [4]. A 2015 systematic review of 6 RCTs found short-term weight reductions at single time points in 3 adult trials and no change in BMI in any trial [5], and its authors later published a correction and reanalysis of data errors [6].
Population
Adults and children in RCTs [1]; overweight and obese adults [4][5].
Sources
[1], [4], [5], [6]
Caveats
Sources disagree. Pediatric patients and people already on dietary changes benefited less in [1]. Only one trial in [5] reported an effect at more than one time point.

Not shown to help1

LimitedStudied in children

Weight in children

One trial found no change in BMI z score in children with overweight over 12 weeks. Total and LDL cholesterol were lower.

The numbers and sources
Effect
In 96 children aged 6 to 17 with overweight or obesity, 3 g a day for 12 weeks did not change BMI-for-age z score compared with maltodextrin placebo (mean difference 0.0, 95% CI -0.1 to 0.1). Total and LDL cholesterol were lower with glucomannan at 12 weeks [7].
Population
96 children in Poland [7].
Sources
[7]
Caveats
One trial. It was funded in part by Dicofarm S.p.A. and the Nutricia Foundation, along with the Medical University of Warsaw [7].

Doses studied

The LDL meta-analysis described an intake of about 3 g a day [2]. The pediatric trial used 3 g a day for 12 weeks [7]. The 2008 meta-analysis pooled trials of varying doses [1].

Risks

Reported risks4

LimitedHow often is not known

Esophageal and gut obstruction

Case reports: esophageal blockage after a glucomannan diet aid, and stomach outlet blockage linked to konjac flour noodles.

The numbers and sources
How common
How often is not known: the sources give no rate.
Effect
A 37-year-old woman developed delayed esophageal obstruction after an over-the-counter glucomannan diet aid and cleared it by forceful vomiting just before endoscopy. She was later found to have an esophageal web. The authors describe glucomannan as expanding rapidly to many times its original size and list gastrointestinal obstruction among its reported effects [9]. A 1986 report addressed glucomannan and the risk of esophageal obstruction [10], and a 2018 report described gastric outlet obstruction associated with konjac flour noodles [11].
Population
Case reports [9][10][11].
Sources
[9], [10], [11]
Caveats
Case reports cannot give a rate. The 2007 patient had prior upper gastrointestinal pathology [9]. Abstracts were not available for [10] and [11].
LimitedHow often is not known

Choking on konjac jelly candies

FDA states it warned in 2001 about choking on konjac candy after several deaths. Its import alert covers firm mini-cup jelly candies.

The numbers and sources
How common
How often is not known: the sources give no rate.
Effect
FDA states that in 2001 it warned about the danger of choking caused by konjac candy following several choking deaths, and near-deaths among children and elderly people. Its import alert covers mini-cup gel and jelly candies of firm consistency, including those made with other gelling agents such as carrageenan [12].
Population
US import regulation [12].
Sources
[12]
Caveats
These are candies, not supplement capsules or powders. FDA ties the risk to the candies' shape and firmness [12].
ModerateHow often is not known

Digestive side effects

Weight loss trials reported abdominal discomfort, diarrhea and constipation. In a pediatric trial, adverse events were about as common as on placebo.

The numbers and sources
How common
How often is not known: the sources give no rate.
Effect
Adverse events in weight loss trials included abdominal discomfort, diarrhea and constipation [4]. In the pediatric trial, adverse events did not differ from placebo [7].
Population
RCTs [4][7].
Sources
[4], [7]
Caveats
Event rates are not given in the abstract of [4].
LimitedHow often is not known

Blood pressure in the pediatric trial

One trial found higher blood pressure in children on glucomannan than placebo, while an adult meta-analysis found no change.

The numbers and sources
How common
How often is not known: the sources give no rate.
Effect
Systolic blood pressure at 12 weeks and diastolic pressure at 24 weeks were higher with glucomannan than with placebo in children [7]. In the 2008 adult meta-analysis, blood pressure did not change [1].
Population
96 children [7]; adults and children in RCTs [1].
Sources
[1], [7]
Caveats
A secondary outcome in one trial. Sizes are not given in the abstract.

Claims tested and not found

  1. That glucomannan helps children lose weight. BMI-for-age z score did not change compared with placebo over 12 weeks [7].
  2. That glucomannan lowers apolipoprotein B. Six trials showed no change [2].
  3. That glucomannan lowers blood pressure. Pooled blood pressure did not change [1].

Sources

  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. American Journal of Clinical Nutrition. 2008. https://doi.org/10.1093/ajcn/88.4.1167
  2. Ho HVT, Jovanovski E, Zurbau A, et al. 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. American Journal of Clinical Nutrition. 2017. https://doi.org/10.3945/ajcn.116.142158
  3. Jazinaki MS, Rafiei H, Bahari H, et al. Effects of Glucomannan on Cardiometabolic Parameters in Adults With Insulin Resistance-Related Conditions: A Systematic Review and Dose-Response Meta-Analysis. Food Science & Nutrition. 2026. https://doi.org/10.1002/fsn3.72460
  4. 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. Journal of the American College of Nutrition. 2014. https://doi.org/10.1080/07315724.2014.870013
  5. Zalewski BM, Chmielewska A, Szajewska H. The effect of glucomannan on body weight in overweight or obese children and adults: A systematic review of randomized controlled trials. Nutrition. 2015. https://doi.org/10.1016/j.nut.2014.09.004
  6. Zalewski BM, Chmielewska A, Szajewska H, et al. Correction of data errors and reanalysis of "The effect of glucomannan on body weight in overweight or obese children and adults: A systematic review of randomized controlled trials". Nutrition. 2015. https://doi.org/10.1016/j.nut.2015.02.008
  7. Zalewski BM, Szajewska H. No Effect of Glucomannan on Body Weight Reduction in Children and Adolescents with Overweight and Obesity: A Randomized Controlled Trial. Journal of Pediatrics. 2019. https://doi.org/10.1016/j.jpeds.2019.03.044
  8. 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. European Journal of Nutrition. 2025. https://doi.org/10.1007/s00394-025-03826-3
  9. Vanderbeek PB, Fasano C, O'Malley G, et al. Esophageal obstruction from a hygroscopic pharmacobezoar containing glucomannan. Clinical Toxicology. 2007. https://doi.org/10.1080/15563650601006215
  10. Henry DA, Mitchell AS, Aylward J, et al. Glucomannan and risk of oesophageal obstruction. BMJ. 1986. https://doi.org/10.1136/bmj.292.6520.591-a
  11. Jackman C, Waddell R, Fisher L, et al. Konjac flour noodles associated with gastric outlet obstruction. Emergency Medicine Australasia. 2018. https://doi.org/10.1111/1742-6723.12932
  12. U.S. Food and Drug Administration. Import Alert 33-15: Detention Without Physical Examination of Mini-cup Gel and Jelly Candies of Firm Consistency that Present Risk of Choking. 2026. https://www.accessdata.fda.gov/cms_ia/importalert_105.html

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