Glucomannan (konjac)
Summary
Glucomannan is a highly water-absorbing fibre from konjac root. About 3 g a day lowered LDL cholesterol by about 10% in 12 trials, but a meta-analysis of 8 trials in overweight adults found no significant weight loss. Because it swells rapidly, a glucomannan diet aid has caused oesophageal blockage. Abdominal discomfort, diarrhoea and constipation were reported.
Key facts
- The main polysaccharide of the konjac tuber; it holds large amounts of water and forms a viscous gel[3]
- 12 trials (370 people): LDL −0.35 mmol/L (about 10%) and non-HDL −0.32 mmol/L at about 3 g/day; apolipoprotein B unchanged[1]
- 8 trials in overweight or obese adults: −0.22 kg versus placebo, not significant[2]
- Hygroscopic glucomannan diet products have caused oesophageal obstruction[3]
- 1 graded human outcome on this page
- October 11, 2026
How it works
ProposedGlucomannan forms a viscous gel and swells in the gut; this is the proposed basis of its cholesterol-lowering and fullness effects.[3][1]
What the human research says
Human trials only, one row per outcome. The form column shows what each trial actually tested. Grades follow our evidence-grading policy.
| Outcome | Effect | Grade | Best evidence | PMID |
|---|---|---|---|---|
| LDL and non-HDL cholesterol | Improved | Grade B | Meta-analysis · n = 370 · 2017 Adults and children in 12 randomized trials of at least 3 weeks Form: Konjac glucomannan · Dose: About 3 g/day · Duration: At least 3 weeks LDL fell 0.35 mmol/L (about 10%) and non-HDL 0.32 mmol/L versus control; apolipoprotein B did not change in 6 trials. | 28356275 (opens PubMed)Source [1] |
Forms
| Form | Elemental % | Absorption (human data) | GI tolerance | Studied for |
|---|---|---|---|---|
| Glucomannan capsules or powder | Varies | Swells in the gut after it is swallowed; no absorption data in the sources cited here.[3] | Abdominal discomfort, diarrhoea and constipation reported; tablets have caused oesophageal blockage.[2][3] | Cholesterol and weight trials |
Studied doses
Doses studied in human trials ranged from about 3 g of glucomannan per day in the pooled cholesterol trials, which lasted at least 3 weeks; weight-loss trials used varied doses.[1][2]
Interactions
Published interactions only: each row cites a source. No row means none was found in our sources, not that a combination is safe.
None found in our sources.
Who should be careful
- Swallowing problems or oesophageal narrowing
- A glucomannan diet product swelled and blocked the oesophagus in a woman with an oesophageal web.[3]
- Dry or delayed swallowing of tablets
- Glucomannan absorbs water and expands rapidly; a diet aid caused a delayed oesophageal blockage.[3]
- People taking other medicines
- The case report notes glucomannan may change how well other medicines are absorbed.[3]
Talk to your pharmacist or clinician before starting a supplement, especially if you take prescription medicines.
Frequently asked questions
Does glucomannan help weight loss?
A meta-analysis of 8 trials in overweight adults found no significant weight loss versus placebo (−0.22 kg).[2]
Does glucomannan lower cholesterol?
Yes, modestly: about 3 g a day lowered LDL by about 10% in 12 trials.[1]
Is glucomannan safe?
Stomach upsets are common, and because it swells, tablets have caused oesophageal blockage.[2][3]
Is konjac the same as glucomannan?
Glucomannan is the main fibre extracted from the konjac tuber.[3]
Sources
- [1]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. meta-analysis
- [2]The efficacy of glucomannan supplementation in overweight and obesity: a systematic review and meta-analysis of randomized clinical trials. J Am Coll Nutr, 2014. meta-analysis
- [3]Esophageal obstruction from a hygroscopic pharmacobezoar containing glucomannan. Clin Toxicol (Phila), 2007. observational
What changed
- New monograph. Every PMID checked against NCBI E-utilities (title, journal and year from the PubMed record); each evidence row written from its abstract; intake and safety facts from the cited fact sheets.