Glucomannan

What is it?

Glucomannan is a water-soluble dietary fibre that is derived from konjac root (Amorphophallus konjac). Like other forms of dietary fibre, 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.

Good results have been noted in preliminary1 and double-blind studies2 3 4 5 of glucomannan for the treatment of constipation. In constipated individuals, glucomannan and other bulk-forming laxatives generally help produce a bowel movement within 12 to 24 hours.6 The use of glucomannan for diverticular disease of the colon has also been studied in preliminary research; about one-third to one-half of the subjects were found to benefit from glucomannan.7

Glucomannan delays stomach emptying, leading to a more gradual absorption of dietary sugar; this effect can reduce the elevation of blood sugar levels that is typical after a meal.8 Controlled studies have found that after-meal blood sugar levels are lower in people with diabetes given glucomannan in their food,9 and overall diabetic control is improved with glucomannan-enriched diets according to preliminary10 and controlled11 12 trials. One preliminary report suggested that glucomannan may also be helpful in pregnancy-related diabetes.13 One double-blind study reported that glucomannan (8-13 grams per day) stabilized blood sugar in people with the insulin resistance syndrome (syndrome X).14 In a preliminary study,15 addition of either 2.6 or 5.2 grams of glucomannan to a meal prevented hypoglycaemia in adults with previous stomach surgery; a similar study of children produced inconsistent results.16

Like other soluble fibres, glucomannan can bind to bile acids in the gut and carry them out of the body in the faeces, which requires the body to convert more cholesterol into bile acids.17 This can result in the lowering of blood cholesterol and other blood fats. Controlled18 19 and double-blind20 21 studies have shown that supplementation with several grams per day of glucomannan significantly reduced total blood cholesterol, LDL (“bad”) cholesterol, and triglycerides, and in some cases raised HDL (“good”) cholesterol. One double-blind study reported that glucomannan (8-13 grams per day) lowered total and LDL cholesterol in people with the insulin resistance syndrome.22

Glucomannan may help weight loss by occupying space in the stomach, thereby making a person feel full. One double-blind study reported weight loss averaging 5.5 pounds in adults when one gram of glucomannan was taken with a cup of water one hour before each meal for eight weeks.23 However, a similar study of overweight children found that glucomannan was not significantly more effective than a placebo.24 Other controlled studies have found that glucomannan improves the results of weight loss diets in overweight adults25 and children.26

Where is it found?

Glucomannan is a purified fibre from konjac root that is available as a bulk powder or in hard-gelatine capsules. Whether any foods contain significant amounts of glucomannan is unclear.

Glucomannan has been used in connection with the following conditions (refer to the individual health concern for complete information):

Rating Health Concerns
3Stars

Constipation

Diabetes

High blood cholesterol

Insulin resistance syndrome (Syndrome X)
2Stars

Obesity
1Star

Diverticular disease

Hypoglycaemia
3Stars Reliable and relatively consistent scientific data showing a substantial health benefit.
2Stars Contradictory, insufficient, or preliminary studies suggesting a health benefit or minimal health benefit.
1Star 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.27 28 Effective amounts for lowering blood cholesterol have been 4–13 grams per day.29 30 31 For controlling blood sugar, 500–700 mg of glucomannan per 100 calories in the diet has been used successfully in controlled research.32 33 For weight loss, 1 to 3 grams before each meal has been effective.34 35 When using glucomannan and other dietary fibre 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 oesophagus (the tube leading from the mouth to the stomach) should not take any fibre supplement in a pill form, as the supplement may expand in the oesophagus and lead to obstruction.36 Preliminary reports in humans, as well and animal research, suggest that some people may be sensitive to inhaled glucomannan powder.37

Since intestinal bacteria ferment water-soluble fibres, a great deal of intestinal wind may be produced in individuals not accustomed to a high fibre diet, leading to flatulence and abdominal discomfort.

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

References

1. 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.

2. Marzio L, Del Bianco R, Donne M, et al. Mouth-to-cecum transit time in patients affected by chronic constipation: Effect of glucomannan. Am J Gastroenterol 1989;84:888-91.

3. 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].

4. Signorelli P, Croce P, Dede A. A clinical study of the use of a combination of glucomannan with lactulose in the constipation of pregnancy. Minerva Ginecol 1996;48:577-82 [in Italian].

5. Staianno A, Simeone D, Giudice ED, et al. Effect of the dietary fiber glucomannan on chronic constipation in neurologically impaired children. J Pediatr 2000;136:41-5.

6. Marzio L, Del Bianco R, Donne M, et al. Mouth-to-cecum transit time in patients affected by chronic constipation: Effect of glucomannan. Am J Gastroenterol 1989;84:888-91.

7. Papi C, Ciaco A, Koch M, Capurso L. Efficacy of rifaximin in the treatment of symptomatic diverticular disease of the colon. A multicentre double-blind placebo-controlled trial. Aliment Pharmacol Ther 1995;9:33-9.

8. Doi K. Effect of konjac fibre (glucomannan) on glucose and lipids. Eur J Clin Nutr 1995;49(Suppl. 3):S190-7 [review].

9. Melga P, Giusto M, Ciuchi E, et al. Dietary fiber in the dietetic therapy of diabetes mellitus. Experimental data with purified glucomannans. Riv Eur Sci Med Farmacol 1992;14:367-73 [in Italian].

10. Huang CY, Zhang MY, Peng SS, et al. Effect of Konjac food on blood glucose level in patients with diabetes. Biomed Environ Sci 1990;3:123-31.

11. 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.

12. Vorster HH, Lotter AP, Odendaal I, et al. Benefits from supplementation of the current recommended diabetic diet with gel fibre. Int Clin Nutr Rev 1988;8:140-6.

13. Cesa F, Mariani S, Fava A, et al. The use of vegetable fibers in the treatment of pregnancy diabetes and/or excessive weight gain during pregnancy. Minerva Ginecol 1990;42:271-4 [in Italian].

14. 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.

15. Hopman WP, Houben PG, Speth PA, Lamers CB. Glucomannan prevents postprandial hypoglycaemia in patients with previous gastric surgery. Gut 1988;29:930-4.

16. Kneepkens CM, Fernandes J, Vonk RJ. Dumping syndrome in children. Diagnosis and effect of glucomannan on glucose tolerance and absorption. Acta Paediatr Scand 1988;77:279-86.

17. Wu J, Peng SS. Comparison of hypolipidemic effect of refined konjac meal with several common dietary fibers and their mechanisms of action. Biomed Environ Sci 1997;10:27-37.

18. 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.

19. Zhang MY, Huang CY, Wang X, et al. The effect of foods containing refined Konjac meal on human lipid metabolism. Biomed Environ Sci 1990;3:99-105.

20. 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.

21. Walsh DE, Yaghoubian V, Behforooz A. Effect of glucomannan on obese patients: a clinical study. Int J Obes 1984;8:289-93.

22. 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.

23. Walsh DE, Yaghoubian V, Behforooz A. Effect of glucomannan on obese patients: a clinical study. Int J Obes 1984;8:289-93.

24. Vido L, Facchin P, Antonello I, et al. Childhood obesity treatment: double blinded trial on dietary fibres (glucomannan) versus placebo. Padiatr Padol 1993;28:133-6.

25. 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].

26. Livieri C, Novazi F, Lorini R. The use of highly purified glucomannan-based fibers in childhood obesity. Pediatr Med Chir 1992;14:195-8 [in Italian].

27. 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].

28. 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.

29. 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.

30. 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.

31. 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.

32. 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.

33. 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.

34. Walsh DE, Yaghoubian V, Behforooz A. Effect of glucomannan on obese patients: a clinical study. Int J Obes 1984;8:289–93.

35. 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].

36. Henry DA, Mitchell AS, Aylward J, et al. Glucomannan and risk of oesophageal obstruction. Br Med J 1986;292:591–2.

37. Werley MS, Burleigh-Flayer H, Mount EA, Kotkoskie LA. Respiratory sensitization to konjac flour in guinea pigs. Toxicology 1997;124:115–24.