Glucomannan is a water-soluble dietary fiber that is derived from konjac root (Amorphophallus konjac). Like other forms of dietary fiber, glucomannan is considered a “bulk-forming laxative.” Glucomannan promotes a larger, bulkier stool that passes through the colon more easily and requires less pressure—and subsequently less straining—to expel.
Where is it found?
Glucomannan is a purified fiber from konjac root that is available as a bulk powder to be taken in hard-gelatin capsules or used as an ingredient in food.
Glucomannan has been used in connection with the following conditions (refer to the individual health concern for complete information):
| Science Rating | Health Concerns |
|---|---|
 | Constipation High blood cholesterol Insulin resistance syndrome (Syndrome X) Type 2 diabetes |
 | Obesity |
 | Diverticular disease Hypoglycemia Type 1 diabetes |
| Reliable and relatively consistent scientific data showing a substantial health benefit. Contradictory, insufficient, or preliminary studies suggesting a health benefit or minimal health benefit. For an herb, supported by traditional use but minimal or no scientific evidence. For a supplement, little scientific support and/or minimal health benefit. | |
Who is likely to be deficient?
As glucomannan is not an essential nutrient, no deficiency state exists.
How much is usually taken?
The amount of glucomannan shown to be effective as a laxative is 3–4 grams per day.1 2 Effective amounts for lowering blood cholesterol have been 4–13 grams per day.3 4 5 For controlling blood sugar, 500–700 mg of glucomannan per 100 calories in the diet has been used successfully in controlled research.6 7 For weight loss, 1 to 3 grams before each meal has been effective.8 9 When using glucomannan and other dietary fiber supplements, it is best to start out with a small amount and increase gradually. It is recommended to drink at least 8 ounces of water each time any bulk-forming laxative, including glucomannan, is taken.
Are there any side effects or interactions?
People with any disorder of the esophagus (the tube leading from the mouth to the stomach) should not take any fiber supplement in a pill form, as the supplement may expand in the esophagus and lead to obstruction.10 Preliminary reports in humans, as well and animal research, suggest that some people may be sensitive to inhaled glucomannan powder.11
Since intestinal bacteria ferment water-soluble fibers, a great deal of intestinal gas may be produced in individuals not accustomed to a high fiber diet, leading to flatulence and abdominal discomfort.
References
1. Marsicano LJ, Berrizbeitia ML, Mondelo A. Use of glucomannan dietary fiber in changes in intestinal habit. G E N 1995;49:7–14 [in Spanish].
2. Passaretti S, Franzoni M, Comin U. et al. Action of glucomannans on complaints in patients affected with chronic constipation: a multicentric clinical evaluation. Ital J Gastroenterol 1991;23:421–5.
3. Arvill A, Bodin L. Effect of short-term ingestion of konjac glucomannan on serum cholesterol in healthy men. Am J Clin Nutr 1995;61:585–9.
4. Vuksan V, Jenkins DJ, Spadafora P, et al. Konjac-mannan (glucomannan) improves glycemia and other associated risk factors for coronary heart disease in type 2 diabetes. A randomized controlled metabolic trial. Diabetes Care 1999;22:913–9.
5. Vuksan V, Sievenpiper JL, Owen R, et al. Beneficial effects of viscous dietary fiber from Konjac-mannan in subjects with the insulin resistance syndrome: results of a controlled metabolic trial. Diabetes Care 2000;23:9–14.
6. Vuksan V, Jenkins DJ, Spadafora P, et al. Konjac-mannan (glucomannan) improves glycemia and other associated risk factors for coronary heart disease in type 2 diabetes. A randomized controlled metabolic trial. Diabetes Care 1999;22:913–9.
7. Vuksan V, Sievenpiper JL, Owen R, et al. Beneficial effects of viscous dietary fiber from Konjac-mannan in subjects with the insulin resistance syndrome: results of a controlled metabolic trial. Diabetes Care 2000;23:9–14.
8. Walsh DE, Yaghoubian V, Behforooz A. Effect of glucomannan on obese patients: a clinical study. Int J Obes 1984;8:289–93.
9. Vita PM, Restelli A, Caspani P, Klinger R. Chronic use of glucomannan in the dietary treatment of severe obesity. Minerva Med 1992;83:135–9 [in Italian].
10. Henry DA, Mitchell AS, Aylward J, et al. Glucomannan and risk of oesophageal obstruction. Br Med J 1986;292:591–2.
11. Werley MS, Burleigh-Flayer H, Mount EA, Kotkoskie LA. Respiratory sensitization to konjac flour in guinea pigs. Toxicology 1997;124:115–24.
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2006-09-07
