Glucomannan (Konjac)
Amorphophallus konjac
Highly viscous konjac soluble fiber that lowers LDL and curbs appetite
Evidence tier
Strong
Research weight
Citations
10 verified / 10
Classification
Prebiotics & Fibers
❝
What the evidence says. Multiple high-quality RCTs / meta-analyses with consistent effects.
What is Glucomannan (Konjac)?
Glucomannan (Konjac) (Amorphophallus konjac) is a prebiotic fiber used for lowers ldl and non-hdl cholesterol: ~3 g/day reduces ldl-c by about 0.35 mmol/l (~10%) and non-hdl-c by ~0.32 mmol/l in rct meta-analyses, via its high viscosity binding bile acids and reducing cholesterol reabsorption. NutriDex grades the human evidence as Strong. Glucomannan is a highly viscous, water-soluble, fermentable dietary fiber extracted from the tuber of the konjac plant (Amorphophallus konjac). Its strongest human evidence is for cholesterol lowering: meta-analyses of randomized controlled trials show that roughly 3 g/day reduces LDL cholesterol by about 0.35 mmol/L (~10%) and non-HDL cholesterol similarly, which is why EFSA authorizes a normal-blood-cholesterol maintenance claim at 4 g/day. It modestly lowers fasting glucose and produces small short-term weight loss, though weight-loss meta-analyses are mixed and effects are not durable. Because it forms a thick gel on contact with water, it carries a distinct choking/esophageal-obstruction hazard and must be taken with ample fluid.
Purported Benefits
✓Lowers LDL and non-HDL cholesterol: ~3 g/day reduces LDL-C by about 0.35 mmol/L (~10%) and non-HDL-C by ~0.32 mmol/L in RCT meta-analyses, via its high viscosity binding bile acids and reducing cholesterol reabsorption
✓Underpins an EFSA-authorized health claim that 4 g/day glucomannan helps maintain normal blood cholesterol concentrations
✓Modestly improves glycemic control: meta-analyses show small reductions in fasting blood glucose (~0.6 mmol/L) by slowing gastric emptying and blunting post-prandial glucose absorption
✓Promotes satiety and short-term weight loss: gel formation in the stomach increases fullness; some RCT meta-analyses report ~1 kg greater weight loss versus placebo over <=8 weeks (effect is modest and inconsistent)
✓Increases stool frequency and relieves constipation by adding viscous, water-holding bulk; fermentation yields short-chain fatty acids and supports a bifidogenic gut-microbiome shift
✓Reduces post-prandial triglyceride and glycemic responses when taken before meals
Evidence by outcome
The same supplement can be well-proven for one use and unproven for another — here is the human evidence graded outcome by outcome.
| Outcome | Evidence | Effect | Studies |
|---|---|---|---|
| Lowers LDL and non-HDL cholesterolMultiple RCT meta-analyses: ~3 g/day lowers LDL ~0.35 mmol/L; EFSA authorizes a cholesterol claim at 4 g/day. | Strong | ↑ benefit · moderate | 3 |
| Improved glycemic control (fasting glucose)Meta-analyses show small fasting-glucose reductions, with clearer effect in type 2 diabetics. | Moderate | ↑ benefit · small | 2 |
| Short-term weight lossSome meta-analyses show ~1 kg loss in short trials; Onakpoya 2014 found no significant effect (-0.22 kg). | Mixed | ↔ mixed · small | 2 |
| Constipation relief / increased defecation frequencyIn children, glucomannan raised defecation frequency but did not improve consistency or overall success. | Mixed | ↑ benefit · small | 1 |
| Reduced postprandial triglyceride/glycemic responseLipid/glucose meta-analysis supports lowered triglycerides; postprandial-specific data are limited. | Preliminary | ↑ benefit · small | 1 |
Dosing & Compounds
Typical Dose
For cholesterol and weight: ~3-4 g/day, divided into doses of about 1 g taken 15-60 minutes before each main meal, each with 1-2 full glasses of water. EFSA's cholesterol claim is set at 4 g/day; trials range from ~3 to 15 g/day. Start low and increase gradually to limit gas/bloating.
Active Compounds
Safety & Cautions
Generally well tolerated; common effects are bloating, flatulence, loose stools or mild abdominal discomfort because it is fermentable (a FODMAP-type fiber). The signature hazard is choking and esophageal or throat obstruction: the dry fiber expands rapidly into a gel, so tablets/powder must be taken with plenty of water and avoided by anyone with swallowing difficulty or esophageal narrowing; konjac mini-cup gel candies have caused fatal choking (subject to FDA import alerts and bans for children/elderly). Its viscosity can delay or reduce absorption of co-ingested oral medications, so separate drugs by at least 1-2 hours. People on glucose-lowering or lipid drugs should monitor, and those with strictures, dysphagia, or prior GI surgery should be cautious. Educational only — always check with your doctor or pharmacist before combining Glucomannan (Konjac) with any medicine.
Glucomannan (Konjac) drug interactions
Known or theoretical interactions between Glucomannan (Konjac) and common medications — educational, not exhaustive. Always check with your doctor or pharmacist before combining Glucomannan (Konjac) with any medicine.
Caution
Highly viscous fiber can reduce/delay absorption of medications taken at the same time.
Konjac glucomannan forms a thick gel that traps drugs and slows gastric emptying. Sood — Glucomannan on lipids/glucose (meta-analysis)
Key Studies ★ 10 studies
GRADE-assessed systematic review and meta-analysis
GRADE meta-analysis 2024 (RCTs)
✓ Source
GRADE-assessed pooled analysis confirmed glucomannan supplementation significantly improves the lipid profile, lowering total and LDL cholesterol versus control in adults.
Meta-analysis of RCTs
Guo et al. 2023 (T2DM, meta-analysis)
✓ Full text
In type 2 diabetics, glucomannan supplementation significantly reduced fasting blood glucose and improved lipid parameters compared with control across pooled RCTs.
Systematic review and meta-analysis of RCTs
Mohammadpour et al. 2020 (RCTs)
✓ Full text
In overweight/obese adults, glucomannan produced a significant but modest weight reduction (WMD -0.96 kg; 95% CI -1.81 to -0.11), with larger effects in women and short (<=8 week) trials.
Systematic review and meta-analysis of RCTs
Ho et al. 2017 (n=370, 12 RCTs)
✓ Source
Konjac glucomannan at a median 3.0 g/day lowered LDL cholesterol by 0.35 mmol/L (95% CI -0.46 to -0.25) and non-HDL cholesterol by 0.32 mmol/L versus control, with no effect on apolipoprotein B.
Systematic review and meta-analysis of RCTs
Zalewski et al. 2017 (n=122, 3 RCTs)
✓ PubMed
In children with functional constipation, glucomannan moderately increased defecation frequency but did not significantly improve stool consistency or overall treatment success.
Systematic review and meta-analysis of RCTs
Onakpoya et al. 2014 (n=531, 9 RCTs)
✓ Source
Meta-analysis found a non-statistically-significant difference in body weight between glucomannan and placebo (mean difference -0.22 kg), concluding it does not generate significant weight loss.
Systematic review and meta-analysis of RCTs
Sood et al. 2008 (n=531, 14 RCTs)
✓ PubMed
Glucomannan significantly reduced total cholesterol (-0.5 mmol/L), LDL-C (-0.4 mmol/L), triglycerides, body weight (-0.79 kg) and fasting blood glucose, but not HDL-C or blood pressure.
Regulatory scientific opinion
EFSA NDA Panel 2010
✓ Source
EFSA concluded a cause-and-effect relationship between glucomannan and maintenance of normal blood cholesterol, authorizing a claim conditional on 4 g/day intake, with a mandatory choking warning for inadequate fluid intake.
Review
Bai 2026
✓ PubMed
Critical review of konjac glucomannan's structure-function relationships and emerging biomedical applications.
Review
Yoon 2026
✓ PubMed
Psyllium and Glucomannan as Viscous Fiber Modulators of the Gut-Microbiome-Incretin Axis: Molecular Links to Metabolic Inflammation, Barrier Function, and GLP-1 Receptor Agonist Therapy