Glucomannan is a water-soluble dietary fibre extracted from the root of the konjac plant (Amorphophallus konjac). It is one of the most viscous dietary fibres known, absorbing up to 50 times its weight in water. The European Food Safety Authority (EFSA) has approved a health claim for glucomannan contributing to weight loss when consumed as part of an energy-restricted diet. Multiple randomised controlled trials support its effectiveness.
How it works
Glucomannan works through three mechanisms: (1) It forms a viscous gel in the stomach that delays gastric emptying, promoting feelings of fullness and reducing food intake. (2) It slows carbohydrate absorption, blunting postprandial blood glucose spikes and insulin secretion. (3) It acts as a prebiotic, feeding beneficial gut bacteria that produce short-chain fatty acids (SCFAs), which regulate appetite hormones GLP-1 and PYY.
Evidence-based uses
EFSA-approved health claim: "Glucomannan contributes to weight loss in the context of an energy-restricted diet" (at 3g/day). Systematic reviews show 0.8-1.7kg more weight loss than placebo over 5-8 weeks. Works primarily through increased satiety and reduced caloric intake. Also lowers LDL cholesterol and improves glycaemic control. Must be taken with water — can cause oesophageal obstruction if swallowed dry.
Glucomannan is a potent prebiotic fibre that feeds beneficial gut bacteria (Bifidobacterium, Lactobacillus), increasing SCFA production. Also acts as a bulk-forming laxative for constipation. However, it can cause bloating and gas initially — titrate dose slowly.
Safety
Glucomannan can slow absorption of oral medications by forming a gel barrier in the gut. Take all medications at least 1 hour before or 4 hours after glucomannan.
Glucomannan lowers blood sugar independently. Combined with diabetes medications, it may cause hypoglycemia. Monitor blood sugar more frequently.
MUST be taken with adequate water (250ml+ per dose). Glucomannan can swell and cause obstruction if swallowed dry or without enough liquid. Never take as a dry powder.
Compare prices
3 products compared across Australian retailers. Sorted by price per serve.
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| Product | Price | /serve | |
|---|---|---|---|
Best BulkSupplements Glucomannan Powder (Konjac Root) BulkSupplements | $19.96 | $0.08 | |
Now Foods Glucomannan 575mg iHerb | $14.99 | $0.50 | |
Natrol Glucomannan 500mg iHerb | $11.49 | $0.86 |
Prices in AUD. Some links are affiliate links — we may earn a commission at no extra cost to you.
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Glucomannan has 3 known interactions. Check if it's safe with your medications.
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This information is for educational purposes only and is not intended as medical advice. Always consult a healthcare professional before starting any supplement. Evidence ratings are based on peer-reviewed clinical research. Individual results may vary.