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):
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.
At the time of writing, there were no well-known drug interactions
with glucomannan.
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.