Fibrous glucomannan may assist with weight management by slowing the gastric emptying process.
Glucomannan is a polysaccharide made up of both glucose and mannose that is readily extracted from a handful of different roots, most regularly from that of the konjac plant. Its fibrous nature makes it a compelling supplement for fat loss, suggested to work by:
- Reducing sugar absorption. Glucomannan slows the amount of carbohydrate the digestive system absorbs at one time, promoting the blood sugar stability that’s associated with weight management.
- Acting as an appetite suppressant. Glucomannan absorbs water and swells in the stomach, which may help us eat less by making us feel more full.
Glucomannan (konjac root) is a natural, water-soluble polysaccharide composed of the sugars D-mannose and D-glucose in a 1.6 to 1 ratio and knotted together through β-(1→4) linkage. It is present in the wood of conifers and the roots of certain orchids, but is most commonly extracted for supplemental purposes from the konjac plant, amorphallus konjac, native to tropical locales in eastern Asia.
The starchy konjac root is often pulverized for use as a flour or jelly base for several dishes and soups in eastern asian cuisine, and as a food additive to emulsify and thicken substances. It is also one of the more popular ingredients for fiber-oriented fat-loss supplements.
As a robust dietary fiber, konjac-glucomannan offers a myriad of health benefits linked to weight loss, such as reducing appetite, treating constipation, and curtailing high cholesterol levels — making it an excellent complement to other fat burners.
Since the digestive tract is unable to absorb fiber, glucomannan soaks up water and swells until it forms a kind of bulky gel that fosters a sense of fullness and slows down the speed at which the stomach empties its contents while it expels excess calories and fats.1
Glucomannan Slows Gastric Emptying Time
Research indicates that glucomannan prolongs gastric emptying time, some of the consequences of which are a drop in body weight, a reduction in total plasma glucose after eating, the suppression of hepatic cholesterol synthesis, and an increase in the excretion of bile acids that contain cholesterol.3
Glucomannan convinces the tummy to slow its food processing, and thus supports weight loss by:
As a highly viscous and soluble dietary fiber, konjac root inherently augments gastric water volume when consumed, which subsequently boosts satiety. In turn, bumping up satiety decreases the total amount of cholesterol and glucose intake since less food is eaten. Providing the stomach more time to fulfill its duty allows greater quantities of excess calories to be expelled.4
Slowing Sugar Absorption
Another review suggests that glucomannan slows carbohydrate absorption possibly by inhibiting the breakdown of complex carbohydrates into simple ones, which would hinder their absorption.5 Not only that, the fiber also supposedly helps stabilize blood sugar levels. Maintaining consistent sugar levels wards away unwanted weight gain since fat loves to congregate in the blood when sugar amounts spike.
Managing Cholesterol Absorption
Research points to idea that lower cholesterol levels are a reference for decreased weight gain due to their frequent correlation. One study in particular provides strong evidence that, above all, satiation and satiety effects underlie the cholesterol-lowering properties of dietary fibers.6
The reasoning behind glucomannan’s cholesterol-lowering effect:
- Whether for dietary or satiation purposes, decreased cholesterol levels suggest that less food has been consumed, which more often than not results in weight reduction.
- Decreased cholesterol absorption follows a similar line of thought: less cholesterol absorbed indicates higher satiation.
- Since cholesterol binds to bile acids before excretion, increased expulsion of the duo highlights enhanced metabolism, essential for fat burning.
Glucomannan may hinder absorption of some nutrients.
The capacity of glucomannan to slow the digestive process may, unfortunately, have a negative side effect: Blocking absorption of other nutrition. A study on vitamins reported that glucomannan reduces the intestinal absorption of some fat-soluble vitamins, like vitamins A, D, E, and K, but not that of fat-insoluble vitamins, like vitamin B12.7 For this reason, it is advisable to avoid taking glucomannan and these vitamins at the same exact time.
Glucomannan Fat Burning Benefits & Uses
The principal benefits of glucomannan in terms of fat burning stem from its essence as a vigorous water-soluble fiber.
- Whereas many other fiber sources, such as common fruits and vegetables, hold a combination of soluble and insoluble fibers, the konjac root extract carries a relatively high soluble fiber content, which is ideal for delaying gastric emptying.8
As previously touched on, konjac root helps to alleviate hunger by soaking up heaps of water, which may be why Dr. Oz refers to it as “nature’s skinny sponge.”
That celebrity endorsement has surely helped propel glucommanan to its current reputation as a slimming “fat loss fiber” in many reviews, even though it may not have much of an advantage over other soluble fiber sources.
While Dr. Oz’s endorsement appeals to women who are seeking to lose weight, glucomannan also seems to have a following among bodybuilders who appreciate its help when they “shred” to reduce bodyfat and reveal muscle definition.
Does Glucomannan Diminish Thermogenic Activity?
Thermogenesis is customarily associated with weight loss and can be induced by such factors as exercise, diet, and general states of elevated temperatures. A study examining postprandial thermogenesis concluded that people on a glucomannan diet of 6 grams turned out to have slightly decreased thermogenesis activity compared to those on a different fiber diet. Energy expenditure of 61.4 +/- 8.4 kcal for glucomannan versus 82.3 +/- 5.4 kcal for the other fiber mixture.9
The high number of glucomannan human studies emphasizes its importance in weight management while demonstrating its overwhelming safety.
In this double-blind, placebo-controlled investigation, 200 overweight or obese adults were given a fibrous mixture containing 3 grams of psyllium + 1 gram of glucomannan at either 2 or 3 times a day for 16 weeks. Weight loss was higher in people taking either fiber dose (-4.52 and -4.60 kg) compared to placebo (-0.79 kg), but not to a significant degree. Satiety after eating increased in both fiber groups compared to the placebo. Cholesterol levels lowered more with glucomannan than without.
|Substance||Weight Lost in Pounds|
|Fiber mixture – 3x daily||10.14|
|Fiber mixture – 2x daily||9.96|
- The study concluded that “dietary supplement of soluble fibre in overweight or obese patients was well tolerated, induced satiety and had beneficial effects on some CVD risk factors.”10
This 8-week, double-blind, randomized trial offered either a placebo or konjac root capsules at 1 gram doses with 8 ounces of water 1 hour before each meal to 20 obese adults. The results demonstrated average weight loss as well as cholesterol reduction. Note that the short overall time frame of the study limits its accuracy.
- The study concluded that there was “a significant mean weight loss (5.5 lbs) using glucomannan over an eight-week period.”11
In this randomized study, the behavior of body weight, blood glucose, total serum cholesterol, and hunger and satiety sensation was measured over the course of 60 days during which 30 overweight adults were given either a placebo or glucomannan with their 1,200 kcal diet. The results indicate that glucomannan supplementation facilitates weight loss in low-calorie diets.
- The study concluded that “the low-calorie diet plus glucomannan is more effective than the low-calorie diet alone.”12
In this randomized investigation, 23 obese children were given glucomannan fiber capsules at 1,000 mg twice daily. After 4 months, weight and cholesterol levels dropped with no observable side effects.
- The study concluded that since “excess weight and triglycerides levels were significantly decreased in treated obese patients…highly purified glucomannan fibers may be employed with effectiveness in obese and dyslipidemic children together with diet.”13
In this double-blind, randomized investigation, 60 children under the age of 15-years were given either placebo pills or 1 gram of encapsulated glucomannan twice daily for 2 months. The average percentage of children who were overweight decreased more in the group that took glucomannan from 49.5% to 41% compared to that of the placebo group from 43.9% to 41.7%.
- The study concluded that while “mean overweight of the drug group was decreased…no significant difference was observed between the drug and the placebo groups,” although this was “most likely because of an inadequate water intake”14
In this double-blind, randomized investigation, 30 overweight and obese men either took a placebo or glucomannan capsules at 1,000 mg, 3 times daily for a period of 12 weeks along with a carbohydrate-restricted diet (CRD). At the end, high density lipoprotein cholesterol (HDL-C) and triacylglycerol (TAG) improved significantly by taking the fiber (10% and -34%). Low density lipoprotein cholesterol (LDL-C) decreased by 17.6%.
- The study concluded that “although clearly effective at lowering LDL-C, adding soluble fiber to a CRD during active and significant weight loss provides no additional benefits to the diet alone.”15
Dosage for Weight Control
Glucomannan products you can buy in retail stores may be offered as:
- A powdered capsule supplement (typical of the market), 2 – 4 grams, 30-60 mins before each meal.
- Glucomannan may also be included as an ingredient in some advanced fat-burner stack supplements.
Note: It is critical to take soluble fibers like glucomannan with 8 oz of water for its fat burning power to take effect.
Supplements in Review Recommendation
- Glucomannan, 2 grams
We recommend fibrous glucomannan as the prime fiber supplement for your fat-burning plan. Glucomannan at a total of 2 grams per day taken with 8 ounces of water 30-60 minutes before a meal is our recommended dosage for effective fat burning. The fiber may improve weight loss by minimizing how much sugar your body absorbs and decreasing how much food you crave. Glucomannan is best taken as a supplement to low-calorie diets that do not exclude carbohydrate intake.
Start at 2 grams with 8 oz of water. The human digestive system requires time to acclimate to changing fiber intake, otherwise gastric distress side effects are a certainty. This is why we recommend starting glucomannan supplementation at 2 grams with 8 ounces of water before meals and then gradually moving up dosage based on individual dietary needs. Steady dosing is an easy way to avoid unpleasant digestive stress due to sudden bursts in fiber intake.
- Gonzalez CA, et al. Glucomannan: properties and therapeutic applications. Nutr Hosp.2004 Jan-Feb;19(1):45-50. ↩
- Vuksan V, et al. Konjac-Mannan and American ginsing: emerging alternative therapies for type 2 diabetes mellitus. J Am Coll Nutr. 2001 Oct;20(5 Suppl):370S-80S. ↩
- Doi K. Effect of konjac fibre (glucomannan) on glucose and lipids. Eur J Clin Nutr. 1995 Oct;49 Suppl 3:S190-7. ↩
- Keithley J, Swanson B. Glucomannan and obesity: a critical review. Altern Ther Health Med. 2005 Nov-Dec;11(6):30-4. ↩
- McCarthy MF. Nutraceutical resources for diabetes prevention — an update. Med Hypothesis. 2005;64(1):151-8. ↩
- Van Bennekum AM, et al. Mechanisms of cholesterol-lowering effects of dietary insoluble fibres: relationships with intestinal and hepatic cholesterol parameters. Br J Nutr. 2005 Sep;94(3):331-7. ↩
- Kunhiro D, et al. Influence of Dietary Fiber (Konjac Mannan) on Absorption of Vitamin B12 and Vitamin E. Tohoku J Exp Med. 1983 Dec;141 Suppl:677-81. ↩
- Papathanasopoulos A, Camilleri M. Dietary Fiber Supplements: Effects in Obesity and Metabolic Syndrome and Relationship to Gastrointestinal Functions. Gastroenterology. 2010 Jan;138(1):65-75. ↩
- Salfi L, et al. Effect of dietary fibre on postprandial thermogenesis. Int J Obes.1987;11 Suppl 1:95-9. ↩
- Salas-Salvado J, et al. Effect of two doses of a mixture of soluble fibres on body weight and metabolic variables in overweight or obese patients: a randomised trial. Br J Nutr. 2008 Jun;99(6):1380-7. ↩
- Walsh DE, et al. Effect of glucomannan on obese patients: a clinical study. Int J Obes. 1984;8:289-93. ↩
- Cairella M, Marchini G. Evaluation of the action of glucomannan on metabolic parameters and on the sensation of satiation in overweight and obese patients. Clin Ter. 1995 Apr;146(4):269-74. ↩
- Livieri C, et al. The use of highly purified glucomannan-based fibers in childhood obesity. Pediatr Med Chir. 1992 Mar-Apr;14(2):195-8. ↩
- Vido L, et al. Childhood obesity treatment: double blinded trial on dietary fibres (glucomannan) versus placebo. Padiatr Padol. 1993;28(5):133-6. ↩
- Wood RJ, et al. Effects of a carbohydrate-restricted diet with and without supplemental soluble fiber on plasma low-density lipoprotein cholesterol and other clinical markers of cardiovascular risk. Metabolism. 2007 Jan;56(1):58-67. ↩