Know2eat

Glucomannan

Amorphophallus konjac

Probiotics & Gut

What glucomannan may help with

Ranked by how strong the human evidence is — best supported first.

Best supportedBlood lipid profileModerate evidence· 4 sources

Then, in order

About Glucomannan

A highly viscous soluble fibre from the konjac tuber, capable of absorbing many times its weight in water. It is the gelling agent in shirataki noodles and konjac jelly.

Glucomannan is the most viscous dietary fibre in commercial use, and both its promise and its danger come from that single property. It holds the only authorised European weight-management claim for a fibre — 3 g/day in the context of an energy-restricted diet — though several well-conducted independent trials have found no weight difference against placebo. The safety record is the part that matters most: glucomannan tablets expanding in the oesophagus caused obstructions serious enough that regulators removed tablet products from sale, and cases of oesophageal and intestinal obstruction continue to be reported.

Sold as
Capsule, Powder, Konjac noodles and jelly
Standardised to
Grams of glucomannan; viscosity varies with molecular weight and processing — a product without this marker may not resemble what was studied.
Also known as
Konjac glucomannan, Konjac fibre, Konjac root

Regulation: EFSA authorised a claim that glucomannan contributes to weight loss in the context of an energy-restricted diet at 3 g/day, with mandatory warning wording about choking and taking it with plenty of water. In the US, glucomannan tablets marketed for weight loss were removed after causing oesophageal obstruction; Australia restricted tablet and capsule forms for the same reason. Konjac mini-cup jelly confectionery has been banned or restricted in several countries after choking deaths in children.

What the research used

The amounts, forms and durations published trials of Glucomannan actually administered.

These are the amounts published trials administered — not a recommendation, and not a dose to copy. Trial participants were screened, supervised and given a characterised preparation. What is in a retail bottle is frequently not what was studied, and the amount that suits one person is not general advice.

  • Studied for Weight management

    3–4 g

    Moderate

    Glucomannan daily, in divided doses with 1–2 glasses of water before meals · 8–12 weeks

    The intake behind the authorised European claim. Independent trials have been less favourable, with one well-controlled US trial finding no difference from placebo in weight or body composition over eight weeks.

  • Studied for LDL cholesterol

    3–10 g

    Moderate

    Divided doses daily · 4–8 weeks

    Meta-analyses report LDL reductions in the region of 10% at higher doses, through the same bile-acid mechanism as psyllium. Tolerability limits how many people reach these doses.

This is general information about food, not medical advice. It cannot diagnose, treat or replace guidance from a clinician who knows your history.

When it was taken

Each window says whether a trial compared it against an alternative, or whether it is convention and pharmacology. Most timing advice is the second kind.

Each timing below was actually compared against an alternative in a trial, which is unusual.

  • With food

    Moderate

    Taken before meals with a large volume of water — this is a safety requirement, not a preference. Glucomannan expands up to sixty times its dry volume, and taking it with insufficient fluid, or lying down afterwards, is how oesophageal obstruction happens.

    Timing was tested. A trial compared this window against another and reported a difference.

The evidence in depth

Best supported: Moderate

What each association actually rests on, and the papers behind it. A rating describes the state of the research, not how promising the supplement sounds. How we rate evidence.

Blood lipid profile

Heart Health
Moderate evidence

Meta-analyses report reductions in LDL cholesterol of around 10% with glucomannan, through bile acid sequestration. The lipid evidence is more consistent than the weight evidence, which is the opposite of how the product is marketed.

Moderate evidence. Several human studies point the same way, with real caveats.

View the 4 sources

Deep research mode adds each paper’s own conclusion and stated limitations.

Body composition

Weight Management
Limited evidence

Meta-analyses report small average weight reductions with glucomannan alongside an energy-restricted diet, and EFSA authorised a claim on that basis. Better-controlled independent trials have found no difference from placebo, so the picture is less settled than the authorised claim suggests.

What may be going on: Extreme viscosity slows gastric emptying and increases the volume of stomach contents, plausibly increasing fullness and reducing energy intake.

Limited evidence. Early human work, or mostly lab and animal research.

View the 2 sources

Deep research mode adds each paper’s own conclusion and stated limitations.

Satiety and appetite

Weight Management
Limited evidence

Short trials report increased fullness ratings, consistent with the viscosity mechanism. Translation into sustained reductions in energy intake is inconsistent.

Limited evidence. Early human work, or mostly lab and animal research.

View the 4 sources

Deep research mode adds each paper’s own conclusion and stated limitations.

Things to know

Interactions, contraindications and dose limits, most serious first. Concentrated extracts interact with medication in ways the whole plant does not, so this section carries more weight here than it does on a food page.

  • Worth knowing

    Oesophageal and intestinal obstruction

    Glucomannan swells dramatically and rapidly. Tablet formulations caused enough oesophageal obstructions that regulators removed them from sale in the US and restricted solid forms in Australia, and cases of obstruction from capsules and powder continue to be reported. It must be taken with a large volume of water, never immediately before lying down, and never by anyone with swallowing difficulty, an oesophageal stricture or a history of bowel obstruction.

  • Worth knowing

    Choking risk in konjac confectionery

    Konjac jelly mini-cups have caused choking deaths in children because the gel does not dissolve in the mouth and is firm enough to occlude an airway. Several countries have banned or restricted them.

  • Interaction

    Reduces absorption of medication and may lower blood glucose

    Interacts withSulfonylureas, insulin, levothyroxine, oral medications generally

    A highly viscous gel delays gastric emptying and can substantially reduce absorption of drugs taken with it, including sulfonylureas and other diabetes medication — which combined with its own glucose-lowering effect makes hypoglycaemia a real consideration. Separate medication by at least two hours.

  • Too much

    Bloating, wind and abdominal discomfort

    Common, dose-related and the usual reason people stop before reaching the doses used in the lipid trials.

Evidence ratings on this page: 1 moderate evidence, 2 limited evidence.

Supplements are sold in the US without pre-market review of efficacy or safety. Nothing on this page is a recommendation to take Glucomannan, or a dose to follow.