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Glucomannan

Also known as: Konjac glucomannan, KGM, Amorphophallus konjac, konjac fiber, konjac root

Evidence under review. — Not yet rated

Soluble dietary fiber shown to ease constipation, blunt blood sugar spikes, and support weight loss.

  • What it does

    Glucomannan is a highly viscous soluble fiber extracted from the konjac plant root. It absorbs water in the gut to form a thick gel, which slows digestion, reduces post-meal blood sugar and...

  • Evidence quality

    Evidence base hasn't been formally rated yet. See research below.

  • Clinical dose

    3-5 g daily based on study doses

See full breakdown ↓ Methodology →

What the Science Says

Glucomannan is a highly viscous soluble fiber extracted from the konjac plant root. It absorbs water in the gut to form a thick gel, which slows digestion, reduces post-meal blood sugar and insulin spikes, and adds bulk to stool to relieve constipation. Clinical trials show meaningful improvements in bowel movement frequency, stool consistency, and satiety within weeks of use, with doses typically around 3–5 g per day.

What It Doesn't Do

Not a standalone cure for obesity — weight loss in studies was modest and combined with diet. Won't fix blood sugar on its own if you have diabetes. No evidence it builds muscle or boosts energy. Not a probiotic — it feeds gut bacteria but doesn't contain live cultures. Don't expect overnight results; most studies ran 8–26 weeks.

Evidence-Based Benefits

Significantly improves bowel movement frequency and stool consistency in people with functional constipation.

Moderate Evidence

Effective at: Not precisely defined; 8-week supplementation used in RCT

Reduces post-meal insulin spikes and blunts blood sugar response when taken before a meal.

Moderate Evidence

Effective at: 3 g per dose

Supports modest body weight and fat reduction in people with obesity over several months.

Moderate Evidence

Effective at: Combined fiber supplement over 180 days

Increases beneficial gut bacteria diversity and reduces harmful species linked to constipation.

Weak Evidence

Effective at: 8-week supplementation

Increases feelings of fullness and reduces desire to eat for up to 2.5 hours after consumption.

Weak Evidence

Effective at: 3 g single dose

Absorption & Bioavailability

Poor (as intended) — glucomannan is not absorbed by the body. It works mechanically in the gut by forming a viscous gel. Its effects depend on gut fermentation and physical bulk, not systemic absorption.

Red Flags to Watch For

  • Must be taken with a full glass of water — dry tablets or powder can swell in the throat and cause choking or esophageal blockage
  • Can slow absorption of oral medications — take medications at least 1 hour before or 4 hours after glucomannan
  • May cause bloating, gas, or loose stools, especially when starting supplementation
  • Most clinical studies used glucomannan in combination with other fibers or supplements, making it hard to isolate its effects alone

Research Sources

  • PubMed
  • NIH DSLD

This information is for educational purposes only and is not medical advice. Always consult a healthcare professional before starting any supplement regimen. Last updated: 2026-05-25