A dietary fiber from the tuberous root of the Amorphophallus konjac plant,1 glucomannan has multiple dietary functions. Due to its ability to soak up and hold water, the fiber begins to form a gelatinous mass that expands and fills the stomach.

As it progresses through the stomach and small intestine, this mass induces a feeling of satiety.2 This finding led to industrial interest in using glucomannan as a weight-loss supplement.


Background


Glucomannan is found in several commercial products promoting weight loss. Data from good-quality clinical trials is not available, however, to either support or refute that function. 


The A. konjac plant is a perennial exotic found naturally in most areas of Asia. Called by common names such as Devil’s tongue, it produces a flower with a single, elongated center wrapped in a large leaf. The center spike of the flower and its potato-shaped tuber are two of the parts that are used in nutritional supplements. 



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Due to its unique chemistry, salivary and upper gastric enzymes do not dissolve and break down glucomannan. It is as the fiber passes into the colon that it begins to exert its potent ability to absorb water. By weight, each gram of glucomannan fiber absorbs 50 times its weight in water or more as it passes through the colon and begins a rapid fermentation process.1

Science


Glucomannan begins its expansion in mass and volume immediately after consumption. This property alone increases the feeling of fullness.3 However, further studies indicate that it has even more complex actions involving the hormone ghrelin and the protein leptin.4 Both are major mediators of the hunger-satiety cycle communicating with the brain to dictate hunger.4

In a study of patients with type 2 diabetes, researchers introduced a glucomannan supplement just prior to an oral glucose tolerance test.4 Prandial ghrelin reduction improved and the increase in fasting ghrelin slowed after 4 weeks of supplementation.4

Also, leptin production increased and the rise of postprandial insulin flattened.4 In another study, researchers incorporated 10 g of high-density, glucomannan-based fiber into small biscuits that were eaten before a glucose load.5 The increase in postprandial glucose was reduced by 74% in healthy participants and 63% in patients with diabetes.5

In addition to satiety and reduction in the postprandial glucose spike, glucomannan appears to have a similar impact on lipid metabolism. In a meta-analysis of 14 studies involving more than 530 patients, glucomannan reduced total cholesterol by nearly 20 mg/dL, low-density lipoprotein cholesterol by 15 mg/dL, fasting blood glucose by 7 mg/dL, and triglycerides by 11 mg/dL.6 Considering these impressive metabolic figures, it is interesting to note that the study found an average reduction in body weight of only 0.8 kg (1.76 lbs.).6

Safety, interactions, side effects


Glucomannan can initiate an allergic response, so a small test dose should be considered. The FDA issued several recalls on gummies or other candies that contained glucomannan after at least 6 fatal choking incidents in children.7

Due to its bulk expansion, consumption of large amounts of water are necessary to keep the mass moving through the digestive system. When taken correctly, there will be a mild laxative effect. Insufficient liquid intake can potentially lead to impaction and obstruction.8

There are no known drug interactions. However, there could be unsafe potentiations with medications for cholesterol and glucose control because of their lipid- and glucose-lowering actions.8

Cost, how supplied, dose


Dosing recommendations vary, but the average used in successful studies was 1 g to 7.2 g daily, taken as capsules or tablets before meals.8 


Glucomannan products range from $10 to $20 for a month’s supply. Commercial weight-loss products that contain glucomannan are often significantly more expensive. 


Summary


Health-care providers should give glucomannan products serious consideration as an adjunct to other therapeutic regimens. The statistics on obesity and its comorbid conditions of type 2 diabetes, heart disease, and early mortality are well-known. With more than a third of Americans being overweight or obese, more than 20 million with type 2 diabetes, and more than 8 million with undiagnosed diabetes,9 glucomannan is an inexpensive, palatable option that targets multiple metabolic defects.


References


  1. Keithley JK, Swanson B, Mikolaitis SL, et al. Safety and efficacy of glucomannan for weight loss in overweight and moderately obese adults. J Obes. 2013; Article ID: 610908. Available at hindawi.com/journals/jobe/2013/610908
  2. Vuksan V, Rogovik AL, Jovanovski E, Jenkins AL. Fiber facts: Benefits and recommendations for individuals with type 2 diabetes. Curr Diab Rep. 2009;9(5):405-411.

  3. Kazemipoor M, Radzi CW, Cordell GA, Yaze I. Potential of traditional medicinal plants for treating obesity: A review. Int Conf Nutr Food Sci. 2012;39:164-169. Available at arxiv.org/ftp/arxiv/papers/1208/1208.1923.pdf

  4. Chearskul S, Kreingsinyos W, Kooptiwut S, et al. Immediate and long-term effects of glucomannan on total ghrelin and leptin in type 2 diabetes mellitus. Diabetes Res Clin Pract. 2009;83(2):e40-e42.

  5. Jenkins AL, Jenkins DJ, Wolever TM, et al. Comparable postprandial glucose reductions with viscous fiber blend enriched biscuits in healthy subjects and patients with diabetes mellitus: Acute randomized controlled clinical trial. Croat Med J. 2008;49(6):772-782.

  6. Sood N, Baker WL, Coleman CI. Effect of glucomannan on plasma lipid and glucose concentrations, body weight, and blood pressure: Systematic review and meta-analysis. Am J Clin Nutr. 2008;88(4):1167-1175. Available at ajcn.nutrition.org/content/88/4/1167.long

  7. Inspections, Compliance, Enforcement, and Criminal Investigations: Seizure of “Konjac” Candy. U.S. Food and Drug Administration Center for Food Safety and Applied Nutrition 2002. Page last updated: January 13, 2010. Available at www.fda.gov/ICECI/EnforcementActions/EnforcementStory/EnforcementStoryArchive/ucm105953.htm 

  8. Skidmore-Roth L. Mosby’s Handbook of Herbs & Natural Supplements. 3rd ed. St. Louis, Mo.: Mosby Elsevier; 2006. 

  9. Diabetes Public Health Resource: Number (in Millions) of Civilian, Noninstitutionalized Persons with Diagnosed Diabetes, United States, 1980-2011. Centers for Disease Control and Prevention. Page last updated: March 28, 2013. Available at cdc.gov/diabetes/statistics/prev/national/figpersons.htm

All electronic documents accessed February 3, 2015.