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Viscous soluble fiber from konjac that swells in the stomach to increase fullness and slow gastric emptying.
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.
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.