Supplement
Glucomannan (Konjac Fibre)
A very thick, gel-forming soluble fibre taken from konjac root. It swells sharply when it meets water in the stomach, which is meant to make you feel full. Despite the marketing claims, the pooled trial evidence so far shows no statistically significant weight loss. That is, no result beyond what chance could explain.
Estimated cost
~$15–$30/month
How to take
Capsules or powder 30–60 minutes before meals with a large glass of water — the pre-meal timing requirement adds inconvenience
A systematic review pooled 8 randomised controlled trials and found a weight loss that was not statistically significant vs.
For context — weight loss from prescription medications:
How it works
A thick soluble fibre that soaks up water and swells in the stomach. The bulk it creates may make you feel full and slow the stomach's emptying. By forming a gel that slows digestion, it may also cut calorie absorption slightly.
What the evidence shows
placebo (mean difference –0.22 kg; 95% confidence interval –0.62 to +0.19 kg). In other words, the result could easily be down to chance. The trials also disagreed with each other a lot (high heterogeneity, I²=65%). A few single trials showed a modest benefit. Most showed almost nothing. On the randomised trial evidence available, glucomannan does not show statistically significant weight loss.
The trade-off
What this tends to offer:
- Plausible mechanism (stomach expansion)
- Very affordable (~$15–$30/month)
- Generally safe when taken with adequate water
What this involves:
- No statistically significant weight loss in best available evidence
- Choking risk if taken without sufficient water (EU restriction)
- Must be taken 30–60 minutes before meals, with a large glass of water
- Bloating and GI discomfort reported
Safety
Mostly considered safe. The main risks are gut (GI) side effects: bloating, belly discomfort, diarrhoea, and constipation. Always take it with a large glass of water. There is a documented choking hazard if you swallow it dry, or with too little liquid, above all in tablet or powder form. Because of that risk, the EU has banned glucomannan weight loss claims on tablets.
Community insights
These are personal experiences shared in public online communities — not medical advice.
“Shirataki noodles, also called konjac noodles, are a popular low-calorie stand-in for pasta. Their evidence base is separate from the supplement's. They genuinely help some people eat fewer calories.”
“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
Written and maintained by one person · Built with agentic AI tools · Every number checked against the cited trial · Not medical advice
In the Systematic review and meta-analysis of 8 RCTs, Non-statistically significant weight loss vs. placebo (mean difference –0.22 kg; 95% CI –0.62 to +0.19 kg). High heterogeneity (I²=65%). Available evidence does not support glucomannan as an effective weight loss supplement.
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.
Next step most people take
Built with agentic AI tools and not a substitute for medical advice
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