NutriDex

The Supplement Research Compendium
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Glucomannan (Konjac)

Amorphophallus konjac

Highly viscous konjac soluble fiber that lowers LDL and curbs appetite

Strong evidence 🌾Prebiotics & Fibers🛡️Gut & Immune

✚ Updated · How we grade evidence

Evidence tier
Strong
Research weight
Citations
8 verified / 8
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.

OutcomeEvidenceEffectStudies
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
Standalone capsules/tablets (e.g. Now Foods Glucomannan, NutriZing, Konjac Root) typically 500-665 mg eachPowder for stirring into water or beverages before mealsShirataki / konjac noodles and konjac 'rice' (near-zero-calorie food source)Konjac jelly/gel candies and konjac flour used as a thickener/gelling agent (E425)Fiber blends and meal-replacement/weight-management formulas

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
Oral medications (general)
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

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.
8 sources cited · 8 verified Search all studies on PubMed ↗

Common questions about Glucomannan (Konjac)

What is Glucomannan (Konjac) used for?

Glucomannan (Konjac) is most often taken 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, 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). Highly viscous konjac soluble fiber that lowers LDL and curbs appetite

Does Glucomannan (Konjac) work — what does the evidence say?

Strong evidence. Multiple high-quality RCTs / meta-analyses with consistent effects. 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.

What is the typical dose of Glucomannan (Konjac)?

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.

Is Glucomannan (Konjac) safe? Any cautions or side effects?

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.

How many studies support Glucomannan (Konjac)?

NutriDex cites 8 sources for Glucomannan (Konjac), graded "Strong".

Does Glucomannan (Konjac) interact with any medications?

Yes — known or theoretical interactions include: Oral medications (general — separate dosing) (caution). This is educational and not exhaustive; always check with your doctor or pharmacist before combining Glucomannan (Konjac) with any medicine.

Cite this page
APA

Peh, D. (2026). Glucomannan (Konjac) (Amorphophallus konjac): Benefits, Dosage, Side Effects & Evidence. NutriDex — The Supplement Research Compendium. Retrieved 26 Jun 2026, from https://nutridex.info/s/glucomannan

BibTeX
@misc{nutridex_glucomannan,
  author       = {Peh, Daryl},
  title        = {Glucomannan (Konjac) (Amorphophallus konjac): Benefits, Dosage, Side Effects \& Evidence},
  year         = {2026},
  howpublished = {NutriDex --- The Supplement Research Compendium},
  url          = {https://nutridex.info/s/glucomannan},
  note         = {Reviewed by Dr Daryl Peh, MBBS Singapore, MMed FM. Accessed 2026-06-26}
}

For medical claims, citing the underlying primary studies linked above is preferred. NutriDex is an educational reference, not medical advice.

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