Glucomannan
What it is
Viscous soluble fiber from konjac that swells in the stomach to increase fullness and slow gastric emptying.
What the evidence says
Evidence is weak and inconsistent. An initial 2015 systematic review (Onakpoya et al., 6 RCTs) suggested short-term weight reductions, but the authors' own corrected reanalysis the same year found glucomannan did NOT produce a statistically significant effect on body weight versus placebo. A separate 2014 meta-analysis also reported no significant weight loss. Glucomannan reliably promotes satiety, but high-quality trials do not support meaningful weight loss; it can cause GI side effects and choking risk if taken dry.
About 3 g/day (often 1 g three times daily before meals) with adequate water, as used in trials.
Educational summary of doses studied — not a recommendation. Talk to a clinician before starting any supplement.
Sources (2)
- Correction of data errors and reanalysis of 'The effect of glucomannan on body weight in overweight or obese children and adults: a systematic review of randomized controlled trials' — Nutrition (2015)
- The effect of glucomannan on body weight in overweight or obese children and adults: a systematic review of randomized controlled trials — Nutrition (2015)
Educational summary of published research, checked against primary sources and linked inline. Not medical advice; supplements are not FDA-evaluated to treat disease. See our editorial policy.