Glucomannan (Konjac Fibre)
A highly viscous soluble fibre extracted from konjac root. Expands dramatically when it contacts water in the stomach, intended to promote feelings of fullness. Despite widespread marketing claims, the current meta-analysis evidence does not show statistically significant weight loss.
Quick read · 3 min
- •Evidence: Weak — limited or inconsistent trial data
- •A systematic review and meta-analysis of 8 randomised controlled trials found a non-statistically significant weight loss vs.
- •Generally considered safe.
- •Prescription weight loss drugs produce 7–21% weight loss in trials. Most supplements in this category produce less than 2 kg.
Based on clinical trials · No rankings · Every claim linked to source
Last reviewed: March 2026
How it works
A highly viscous soluble fibre that absorbs water and expands in the stomach, creating bulk that may promote satiety and delay gastric emptying. May also slightly reduce calorie absorption by forming a gel that slows digestion.
What the evidence shows
A systematic review and meta-analysis of 8 randomised controlled trials found a non-statistically significant weight loss vs. placebo (mean difference –0.22 kg; 95% confidence interval –0.62 to +0.19 kg). There was high heterogeneity across trials (I²=65%), meaning results were inconsistent. Some individual trials showed modest benefit; most showed minimal effect. On the available RCT evidence, glucomannan does not demonstrate statistically significant weight loss.
Safety
Generally considered safe. The main risks are GI side effects: bloating, abdominal discomfort, diarrhoea, and constipation. Must always be taken with a large glass of water — there is a documented choking hazard if swallowed dry or with insufficient liquid, particularly in tablet or powder form. The EU has banned glucomannan weight loss claims on tablets due to this risk.
Community insights
These are personal experiences shared in public online communities — not medical advice.
“Shirataki noodles (konjac noodles) are a popular low-calorie pasta substitute with a different evidence base from the supplement — they genuinely help some people reduce calorie intake.”
“Always take it with at least a full glass of water. The choking risk from taking it with too little liquid is real.”
Common questions
After reading this page, most people compare this with other supplements, look at prescription options, or check what they can do today without a prescription.