Glucomannan: Honest Evidence on Weight Loss, Cholesterol & Regularity
Informational summary of published research — not medical advice. If you have a swallowing disorder, esophageal narrowing, or GI condition, talk to your clinician before taking glucomannan. This statement has not been evaluated by the FDA. This product is not intended to diagnose, treat, cure, or prevent any disease.
The EU authorized a weight-loss claim for glucomannan at 3g/day — but the best-designed modern RCT (Keithley 2013) and the most rigorous meta-analysis (Onakpoya 2014) both found no significant weight loss. Glucomannan's cholesterol evidence (Sood 2008, Chen 2003) is meaningfully stronger than its weight-loss evidence. And because glucomannan is unusually viscous and hygroscopic, it carries a real, peer-reviewed-documented choking/esophageal-obstruction risk if taken dry or underhydrated — always take it with a full glass of water. If you're deciding which fiber to take at all, see our fiber comparison; if you're weighing glucomannan against psyllium specifically, see psyllium's deep dive and the comparison below. Glucomannan earns its own page because it's chemically and functionally distinct from psyllium — far more viscous, a different regulatory claim history, and real case-report safety literature psyllium doesn't carry.
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Glucomannan at a glance
- What it is
- Soluble fiber from konjac root (Amorphophallus konjac) — the most viscous, hygroscopic fiber sold as a supplement
- EU weight-loss claim
- 3g/day, three 1g doses with water before meals, in the context of an energy-restricted diet (Reg. (EU) No 432/2012)
- Weight-loss RCT reality
- Null — Keithley 2013 (-0.4kg vs -0.43kg placebo, n.s.) and Onakpoya 2014 meta (MD -0.22kg, n.s.)
- Cholesterol effect
- LDL -15.99 mg/dL (Sood 2008 meta); -20.7% (Chen 2003, p=0.0004)
- Satiety (acute)
- -47% lower energy intake in a single meal (Au-Yeung 2018) — an acute meal substitution (~8g fibre), not sustained daily dosing
- Safety rule
- Always take with ≥8 fl oz water — real esophageal-obstruction case reports, not boilerplate
- Best value
- Plain glucomannan powder, ~$0.05/gram
Four real threads — and why the weight-loss one is the most misunderstood
- Weight loss — the EU regulatory claim vs. the RCT reality, stated plainly. The authorized EFSA claim requires 3g/day (three 1g doses with 1–2 glasses of water before meals) in the context of an energy-restricted diet — it is not a claim that glucomannan alone causes weight loss. And the trial evidence, tested largely without that dietary restriction, is genuinely null: Keithley 2013's placebo-controlled 8-week RCT (n=53) found -0.4kg with glucomannan vs -0.43kg with placebo — "no significant difference." Onakpoya 2014's meta-analysis of 8 RCTs found the same (mean difference -0.22kg, 95% CI −0.62 to 0.19, not significant). See the full reconciliation on does glucomannan actually cause weight loss?
- Cholesterol — the better-supported effect. Sood 2008's meta-analysis of 14 studies (n=531) found LDL cholesterol lowered a weighted mean of -15.99 mg/dL, plus real drops in total cholesterol, triglycerides, and fasting glucose. Chen 2003's smaller RCT (n=22, type 2 diabetics, 3.6g/day) found LDL fell -20.7% (p=0.0004) — directionally consistent, though a single small trial shouldn't be over-anchored to on its own. Full detail on glucomannan for cholesterol.
- Satiety/appetite — a real mechanism that doesn't reliably become weight loss. Au-Yeung 2018's crossover trial found that a gelled meal delivering 8g of konjac fibre (its "100-KGM" arm — konjac-gel noodles replacing 100% of a pasta preload) cut cumulative energy intake -47% vs control in a single meal (P<0.001), with a 4g-fibre meal cutting it 23% — genuine, dose-dependent, and mechanistically exactly why the EFSA claim is plausible. The catch: that fibre was eaten as a gelled-noodle meal (a food, ~97% water), and it's an acute single-meal result, not a multi-week weight-outcome trial at a normal 3g/day supplement dose. It's the mechanism that makes the weight-loss claim plausible in principle — not proof it plays out over weeks of normal dosing.
- Constipation/regularity — directionally positive, the thinnest evidence base of the four. Chen 2006's small RCT (n=8 healthy adults, 4.5g/day, 21 days) found defecation frequency up ~27%, wet stool weight up ~30%, and increased fecal lactobacilli and short-chain fatty acids (all P<0.05) — a genuine prebiotic/laxative signal, worth pairing with probiotic content for the gut-ecology angle. But it's a single 8-person trial, a much thinner base than psyllium's constipation literature — state the confidence honestly.
The water rule — and why it matters more here than for any other fiber on this site
| Item | Value |
|---|---|
| Nutricost | $0.050 |
| BulkSupplements.com | $0.082 |
| Nutricost | $0.157 |
| NOW Foods | $0.160 |
| Nature's Way | $0.188 |
Verified picks
Ranked by cost per gram of glucomannan — the full ranking, including the capsule pill-burden math, is on the best glucomannan supplement page:
Pure powder, 2g per scoop — lets you dose exactly to the 3g EFSA protocol, cheapest cost per gram verified.
Same pure-powder format, no additives, a real per-gram premium over Nutricost.
Cheapest capsule sticker price — about 5 capsules to approximate the 3g EFSA dose, real pill burden.
As an Amazon Associate we earn from qualifying purchases. Picks are ranked by cost per gram of glucomannan, never commissions.
Frequently asked questions
Does glucomannan actually cause weight loss?
The EU authorized a 3g/day weight-loss claim, but the best RCT (Keithley 2013) found no significant weight loss vs. placebo, and Onakpoya 2014's meta of 8 RCTs found the same. The claim and the trial evidence genuinely disagree — full breakdown on the differentiator page.
Does glucomannan lower cholesterol?
Yes — glucomannan's better-supported effect. Sood 2008's meta found LDL down -15.99 mg/dL; Chen 2003 found -20.7% at 3.6g/day. Real, but a risk-marker improvement, not a statin replacement.
Is glucomannan dangerous?
It carries a real, documented esophageal-obstruction risk if taken dry or underhydrated — worse than most fibers because of its high viscosity. Always take with a full glass of water; never dry, never a tablet.
Is this the same as psyllium or the fiber comparison?
No — glucomannan is a distinct, more viscous fiber with its own regulatory claim history and safety profile. See /fiber/ to decide fiber type; this page assumes glucomannan specifically.
Go deeper
Best Glucomannan Supplement
Capsules vs powder, ranked by cost per gram and the real cost to hit the 3g EFSA dose.
Dosage Guide
The EFSA protocol, cholesterol and constipation doses, and the water rule — not optional here.
Glucomannan for Cholesterol
The LDL evidence, which is meaningfully stronger than the weight-loss claim.
Does Glucomannan Cause Weight Loss?
The EFSA claim, reconciled honestly with the null RCTs.
About our data
Every clinical claim here links to its primary source on PubMed, verified against the original abstract. Product picks are ranked by cost per gram of glucomannan from live prices; a machine-readable version is at /glucomannan/cost-by-brand.json (CC BY 4.0). See our methodology and editorial standards.
Sources
- 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. PMID: 24490058
- 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. PMID: 24533610
- 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. PMID: 18842808
- Chen HL, Sheu WH, Tai TS, Liaw YP, Chen YC. "Konjac supplement alleviated hypercholesterolemia and hyperglycemia in type 2 diabetic subjects — a randomized double-blind trial." J Am Coll Nutr. 2003. PMID: 12569112
- Au-Yeung F, Jovanovski E, Jenkins AL, Zurbau A, Ho HVT, Vuksan V. "The effects of gelled konjac glucomannan fibre on appetite and energy intake in healthy individuals: a randomised cross-over trial." Br J Nutr. 2018. PMID: 29202887
- Chen HL, Cheng HC, Liu YJ, Liu SY, Wu WT. "Konjac acts as a natural laxative by increasing stool bulk and improving colonic ecology in healthy adults." Nutrition. 2006. PMID: 17027233
- Vanderbeek PB, Fasano C, O'Malley G, Hornstein J. "Esophageal obstruction from a hygroscopic pharmacobezoar containing glucomannan." Clin Toxicol (Phila). 2007. PMID: 17357389
- Henry DA, Mitchell AS, Aylward J, Fung MT, McEwen J, Rohan A. "Glucomannan and risk of oesophageal obstruction." Br Med J (Clin Res Ed). 1986. PMID: 3004635
- EFSA NDA Panel. Health claim for glucomannan and weight loss, authorized under Regulation (EU) No 432/2012.