Glucomannan | Properties, Contraindications and Weight Loss

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Robert Maurer

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By the healthiergang writer , graduated in Food Science and Technology, majoring in Nutrition and Functional Food.


Glucomannan is a high molecular weight polysaccharide (vegetable fiber) obtained from the tubers of Amorphophallus konjac (a plant belonging to the Araceae family), from a chemical point of view it is made up of molecules of D-glucose and D-mannose joined by bonds? -1,4, and present respectively in a molecular ratio of 1: 1.6.

Structurally it is very similar to cellulose; or to lignin and other pectic substances but unlike cellulose, which is insoluble and absorbs water from 5 to 10 times its weight, Glucomannan is soluble and absorbs water up to 200 times its weight.

Dissolved in water, Glucomannan, by absorbing water and swelling, is able to form a very viscous, gelatinous solution within about 30 minutes, whose viscosity slowly increases to a maximum value after about 4-5 hours (European Bulletin of Drug Research, 2001 vol. 9 (1): 207-211). It is classified as "soluble dietary fiber".

How is it obtained and applied?

As mentioned, it is extracted from the root of Amorphophallus konjac, a plant of oriental origin, very widespread in the Japanese phytotherapeutic tradition.

Only the "third year tubers" will be suitable for the extraction of glucomannan, in fact, the fresh konjac tuber contains an average of 13% of dry matter, of which 2/3 is glucomannan and 1/3 is starch, plus the the tuber will be ripe the more the percentage of glucomannan will rise.

In addition to glucomannan, the Konjac tuber contains lignin, cellulose and other fibers, which will be lost during extraction and purification. Purified glucomannan is a whitish powder that is taken prepared in capsules, tablets or sachets to be dissolved in water at the time of use.

Properties of Glucomannan

After oral intake, only a small amount of glucomannan is digested by the small intestine. Glucomannan, in fact, has the property of resisting the action of digestive enzymes, its degradation therefore takes place in the large intestine, but thanks to the action of colon bacteria.

The action of these bacteria leads to the formation of various metabolites such as formic acid, acetic acid, butyric acid, propionic acid,? -1,4-D-mannobioso, cellobiose, glucose and mannose, which, for the most part, is excreted in the faeces, together with unchanged glucomannan and therefore not absorbed, for this reason it is considered dietary fiber. While butyrate appears to be the only metabolite used for energy by the cells of the colon.

Given its chemical characteristics and consequently properties and mechanisms of action, glucomannan is exploited for its various biological activities through a series of "clinical" applications.

Let's start by saying, in general, that mainly glucomannan preparations are used in the treatment of constipation and in weight control.

To carry out its function, however, it is essential that the intake of the same is coupled with the ingestion of significant quantities of liquids: in constipation its action will be to increase the viscosity of the food bolus, reducing its stay in the intestinal tract and reducing absorption. of nutrients; in weight control, the formation of the gel in the stomach will contribute to the sense of fullness and satiety and modulates the absorption of the food introduced, interfering with the absorption and metabolism of carbohydrates and fats (hypoglycemic and lipid-lowering action).


Before moving on to analyze some studies in the literature a little more specifically, let's see what the contraindications related to the intake of this compound and the dosages may be. First of all, subjects who take other drugs will have to consider the possibility that this may affect the absorption of the same, it is therefore recommended to avoid the concomitant intake of drugs and glucomannan in the period between 30 minutes before and 2 hours after.

It is contraindicated in individuals suffering from intestinal obstruction, difficulty in swallowing and esophageal narrowing and could be associated with abdominal swelling.

Glucomannan and Weight Loss

Let us now try to go into some more specific details on the proven effects of glucomannan using some publications available in the literature.

Most of the studies in the literature have shown how glucomannan, especially when associated with low-calorie diets, is able to reduce the intestinal absorption of carbohydrates and lipids, therefore applicable in the treatment or prevention of overweight and obesity, also such effects seem also affect blood sugar levels, stabilizing them and reducing any spikes.

A 2005 review collected several studies related to the association between glucomannan and obesity, revealing that most of these showed that on average intakes of 2-4g / day of the same could be well tolerated (without producing side effects) and at the same time induced significant weight loss in both obese and overweight subjects, limiting intestinal absorption of lipids and carbohydrates and lowering triglycerides and blood lipoprotein levels.

For example, a clinical study compared Glucomannan and placebo in moderately overweight children, showing a good reduction in body weight. In children treated with Glucomannan, but not in those treated with placebo, a reduced absorption of lipids and a reduction in lipidemia were observed without presenting side effects.

Due to its characteristics and chemical properties, Glucomannan is also used to correct chronic constipation conditions as mentioned above. For example, administration of 3 g / day, coupled with large quantities of water, seems to significantly reduce the intestinal transit time.

It is also known in the literature its prebiotic effect linked to the promotion of the growth of Lactobacilli and Bifidobacteria, considered "good bacteria", inhibiting the growth of Clostridia.

Finally, a latest study evaluated the effects of the combination of physical exercise (total-body program) in an 8-week period of diet with glucomannan supplement (300mg), evaluating effects on weight loss, body composition, blood parameters and physical performance in overweight men and women (BMI> 25) (12 men and 10 women) compared to control subjects (10 men and 10 women) who did not exercise.


In summary, glucomannan, like most dietary fiber-based supplements, seem to have several positive effects on the health of the individual, with the assumption that a healthy and balanced diet is essential, these supplements can certainly in particular cases provide some excellent aids to reach the daily requirement of fiber or to exploit one of the many beneficial effects demonstrated in the literature.

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