Glucomannan (Konjac Root Fiber)
Commonly used for
Weight LossHeart Health
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What is it? / Overview
Glucomannan is a highly viscous, water-soluble fiber that forms a gel in the gut, slowing gastric emptying and nutrient absorption (increasing satiety) and binding bile acids and cholesterol while blunting glucose absorption. Meta-analyses show real lipid and glycemic benefit; the weight-loss evidence is more mixed and modest, generally below the threshold considered clinically meaningful on its own.
How is it used? / Administration
Form: Glucomannan (soluble fiber from Amorphophallus konjac); also as PGX, a proprietary highly viscous blend
Typical dose studied: ~3 g/day (commonly 1 g three times daily before meals) with a full glass of water
Timing: Before meals with ample water -- must be taken with fluid to swell properly in the stomach
The dominant safety issue is choking or GI obstruction risk if not taken with adequate water -- always with a full glass, and caution in any swallowing disorder.
How well does it work? / Evidence
~ Moderate evidence
Who should avoid it?
Avoid with: Dysphagia / Difficulty swallowing
Interacts with: Oral medications generally -- as a very viscous fiber, may delay absorption; separate dosing by 1-2 hours; Insulin, sulfonylureas -- additive glucose-lowering
Already taking it? Reasonable to continue, especially for the lipid/glycemic benefit -- but always with adequate water given the real choking/esophageal-obstruction risk if taken dry or with insufficient fluid.
Research & references
Sood N et al. (2008). Effect of Glucomannan on Plasma Lipid and Glucose Concentrations, Body Weight, and Blood Pressure: Systematic Review and Meta-Analysis. American Journal of Clinical Nutrition. Bessell E et al. (2021). Efficacy of Dietary Supplements Containing Isolated Organic Compounds for Weight Loss. International Journal of Obesity.
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