Citable fact
«Glucomannan» — evidence level C. Dosage: In studies — 1–4 g per day 30 minutes before a meal with plenty of water (at least 250 ml per dose). A 2005 critical review did not confirm sustained weight loss. Source: PMID 16320857, permanent link to the source in the list below.
How it works
A water-soluble polysaccharide fiber from konjac root. In the stomach it forms a gel, slows gastric emptying and nutrient absorption, increasing satiety. The volume of gel formed limits the real effect.
Dosage and intake
In studies — 1–4 g per day 30 minutes before a meal with plenty of water (at least 250 ml per dose). A 2005 critical review did not confirm sustained weight loss.
30 minutes before a meal and always with water: dry powder and capsules without enough fluid can cause esophageal blockage.
Forms
Konjac capsules and powder, often in combination with other fibers; in the food industry it is used as a thickener.
What is confirmed
- A critical review showed that the weight-loss data are weak and heterogeneous; there is no sustained effect
- Fiber in general moderately helps weight control and metabolic health, but this applies to fiber in the diet, not to a separate supplement
- A small reduction in cholesterol and post-meal glycemia is possible
Adverse effects and limitations
- Dry capsules without enough water swell in the esophagus: cases of obstruction have been described
- Gas, bloating, diarrhea and cramps; severity depends on the dose
- Reduces the absorption of drugs and fat-soluble vitamins when taken together
- Products often contain significantly less glucomannan than stated
Interactions
- Reduces drug absorption: they should be taken at least 1–2 hours before or after
- Enhances the effect of glucose-lowering agents; caution in diabetes
Who must not use it
- Under 18 years: Not recommended.
- Pregnancy and lactation: Not recommended: there are insufficient data on safety during pregnancy and lactation.
- esophageal narrowing and swallowing disorders
- diabetes mellitus
- use of oral drugs with a narrow therapeutic window
- exacerbation of GI diseases
Sources
See also
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