What is Glucomannan: Benefits, Risks, How to use [2023 Nutritionist Reviewed] (2024)

What is Glucomannan?

Glucomannan, sometimes called konjac, konjac mannan, or Glucomannan konjac, is a type of soluble fibre, coming from the tuber or root of the konjac plant, otherwise known as elephant yam (or, to give its scientific name, Amorphophallus konjac or Amorphophallus rivieri)^1,2,3,4. The konjac plant is typically found in East and Southeast Asia^2,3,4. Glucomannan konjac is a type of polysaccharide^2,3, which is a type of carbohydrate.

Because we lack the enzymes to break down fibres like Glucomannan, it passes through the gut and is fermented in the colon by colonic bacteria^1,4. It’s also highly water-soluble being able to absorb up to 50 times its weight in water^1,4 making it the most viscous of all known dietary fibres^3,4. It is commonly used for weight management thanks to its ability to promote feelings of fullness when it soaks up water and bulks up the gut^1,4. It has also been found to have several other benefits as we’ll discuss^2,3.

What forms of Glucomannan are there?

Konjac is processed into konjac flour which has been eaten in Asia traditionally for hundreds of years in the form of konjac noodles^2,5. In the Western world however, it is more common to consume konjac Glucomannan as a dietary fibre supplement.

Glucomannan is extracted from the tuber or root of the konjac plant^2,5. Glucomannan supplements may come in the form of a powder, to be mixed with water, or as a cellulose capsule. It is no longer available as a tablet for safety reasons⁴ as explained further below.

What is Glucomannan made from?

Glucomannan is extracted from the tuber or root of the konjac plant, otherwise known as elephant yam^1,2. It is completely natural, plant-based and can be used as a fibre supplement.

What does Glucomannan do?

Glucomannan konjac is a hydrocolloid², which means it turns into a gel in the presence of water. This gel coats the gut and bowel with a protective, defensive covering². The fact that it absorbs water in the gut also allows it to bulk up the gut and promote a feeling of fullness^1,2. It also helps to delay stomach emptying and aid peristalsis in the gut². That’s the action of the muscles that coat our digestive systems from oesophagus to the anus, which helps the food we eat go through the digestive process. Glucomannan helps to clear the stomach, making sure nothing is left behind, and helps to rid the body of toxins².

Glucomannan is also alkaline meaning it can help to balance the acid/alkaline ratio in the body, something that may benefit those who eat an acidic diet with a lot of meat².

What is the function of Glucomannan supplements?

Glucomannan’s function when used as a dietary supplement is as a water-soluble, highly viscous, fermentable, dietary fibre^1,4.These characteristics of Glucomannan allow it to act as a coating for the digestive tract, to soak up water in the gut, bulk up the gut, improve gut transit time and reduce the absorption of cholesterol^1,2,4.

What is Glucomannan used for?

In the Western world, Glucomannan konjac has been used as a food additive, to act as a thickener and emulsifier in foods, thanks to its gel-like quality when mixed with water, and because it is tasteless and odourless². As a dietary supplement, Glucomannan konjac is used as a dietary fibre supplement, most popularly for weight management.

However systematic reviews of trials have found a number of beneficial effects of konjac. This dietary fibre has been found to be able to reduce blood sugar levels, cholesterol, and blood pressure, as well as act as a prebiotic and a laxative^2,4. This means it has the potential to aid the treatment of a number of disease states including obesity, constipation, type 2 diabetes, inflammation, and cardiovascular disease². The benefits will be discussed in more detail, below.

Is Glucomannan effective?

The European Food Safety Authority has approved the use of Glucomannan as a dietary supplement for weight loss in overweight adults⁶. They carried out an extensive meta-analysis of trials to investigate a number of claims into the use of Glucomannan as a dietary supplement⁶.

The claims investigated included use of Glucomannan for weight management, balancing blood glucose levels, balancing cholesterol levels, and improved bowel function. Their findings were that a cause-and-effect relationship has been scientifically demonstrated when it comes to using Glucomannan supplements for the reduction of body weight, but only when taken correctly. A cause-and-effect relationship was not able to be established to the satisfactory levels for Glucomannan’s other claims due to a lack of evidence.

On the other hand, a more recent systematic review published in 2019 in the Journal of Biological Macromolecules² concluded that Glucomannan consumed regularly does appear to have a beneficial effect on blood sugar levels, cholesterol levels and bowel function. Although they did also conclude that more research into the dietary supplement is required.

How to take Glucomannan?

It’s very important to take Glucomannan correctly in order to feel the beneficial effects. This dietary fibre supplement should be taken before meals, with one to two glasses of water, in order for it to exert its pre-load effect⁶. The glasses of water are essential because of the fact it works through absorption with water. It needs to be taken before every meal, three times per day, and daily for at least 5 weeks⁶. When used as a weight loss supplement, it’s also important to take it in conjunction with a calorie-controlled diet⁶.

How long does it take for Glucomannan to work?

It’s important to take Glucomannan regularly for a length of time in order for it to work. When the European Food Safety Authority carried out their systematic review of trials into the use of Glucomannan as a weight loss supplement, they found that the trial that only lasted for 28 days did not find a beneficial effect, whereas the other trials, which lasted between 5 weeks and 3 months, did⁶. Therefore, we recommend taking Glucomannan on a daily basis for at least 5 weeks in order for you to get the beneficial effects.

How long does it take for your body to absorb Glucomannan?

In the trials reviewed by the European Food Safety Authority, the Glucomannan supplement was administered between 15 minutes to 1 hour before meals, in the successful trials⁶. A trial administering participants with Glucomannan alongside meals did not have a positive outcome, therefore this suggests at least 15 minutes is needed in order for your body to absorb the dietary fiber and take effect.

Glucomannan for weight loss

Glucomannan, like other fibres, is very low in calories^1,2,4. This in itself can help to aid weight loss. It’s been found that the amount people eat is linked to a great extent to the weight or bulk of food rather than to its calorific value, so by bulking up on low-calorie fibres, we naturally lower the number of calories consumed, thereby aiding weight loss⁴.

Glucomannan may also aid weight loss by making you feel fuller in various ways. Because it is a soluble fibre, absorbing water and expanding in the gut, this creates feelings of fullness¹. It’s also been found to increase the speed that food reaches the terminal ileum, the part of the digestive tract that releases satiety signals, and it’s been found to increase levels of cholecystokinin, a hormone thought to bring about fat-induced satiety⁴.

Furthermore, Glucomannan has been found to slow the absorption of food in the gut, which in turn slows the release of insulin after eating⁴. A slower release of insulin helps with weight loss since one of the mechanisms of this hormone is to turn the energy we eat into fat to store for later use.

A number of systematic reviews have investigated the evidence surrounding the claim that Glucomannan can aid weight loss, and these have shown strong evidence in favour of the claim^4,6. In particular, Keithley and Swanson wrote a comprehensive critical review on Glucomannan and obesity, highlighting its possible benefits for decreasing the high prevalence of overweight and obesity in the United States⁴. This is also demonstrated by the fact that the European Food Safety Authority have officially approved its use as a dietary supplement for the purposes of weight loss in overweight adults⁶. Their meta-analysis of trials into the use of Glucomannan as a weight loss supplement reviewed a number of trials where participants were administered Glucomannan or a placebo at least three times per day, with a glass of water before meals.

Several trials found that the participants given Glucomannan lost significantly more body weight than the placebo group. Interestingly they found that the only study into use of a Glucomannan as a weight loss supplement in children found no difference in those given Glucomannan compared to the placebo group, as both groups of children lost a significant amount of body weight during the trial. On the other hand, another review, investigating Glucomannan and obesity, did find that some studies had favourable results in children too⁴.

To conclude, the European Commission, has authorised that Glucomannan in the context of an energy-restricted diet contributes to weight loss. The claim may be used only for food that contains 1 g of Glucomannan per quantified portion. The beneficial effect is obtained with a daily intake of 3 g of Glucomannan in three doses of 1 g each, together with 1-2 glasses of water, before meals

Glucomannan for cholesterol

Another benefit of Glucomannan is its beneficial effect on lipids and cholesterol levels^1,7. The risk of cardiovascular disease may be lowered in people taking Glucomannan supplements due to its beneficial effect on lipids including cholesterol and triglyceride levels^7,8. It was found that Glucomannan reduces the absorption of cholesterol in the gut, promoting its excretion¹.

Systematic reviews of trials have found that individuals given Glucomannan had significantly reduced levels of total cholesterol, low-density lipoprotein (LDL cholesterol - sometimes known as our “bad” cholesterol), and triglycerides when compared to a placebo group^4,7. In turn, this has been found to reduce risk of cardiovascular disease⁷.

The European Commission has authorised how Glucomannan contributes to the maintenance of normal blood cholesterol levels. The claim may be used only for food that provides a daily intake of 4 g of Glucomannan⁶.

Glucomannan for Type 2 diabetes

Patients with type 2 diabetes were found to have lowered fasting blood glucose levels when taking Glucomannan, when compared to a placebo group⁸, this could be a result of the slower absorption of food and decreased appetite¹.

A study carried out by Chearskul et al (2007) focused on a Thai population with Type 2 diabetes. Results showed that Glucomannan may be beneficial in reducing the glycaemic and lipid controls in type 2 diabetes⁹.

Additionally, Vuksan et al, found that konjac mannan fiber when added to conventional diabetes treatment may improve glycemic control, blood lipid profile, and blood pressure in high-risk diabetic individuals¹⁰.

Glucomannan for gut health

Konjac Glucomannan has been found to relieve constipation⁵. Participants of a study in China on a low-fibre diet were found to have increased stool frequency when taking konjac Glucomannan as a dietary supplement, compared to the placebo group⁵.

The Chinese study also found that those taking the Glucomannan supplement had improved levels of healthy gut bacteria including lactobacilli and bifidobacteria, and improved concentrations of short-chain fatty acids⁵, suggesting that Glucomannan can also be used as a prebiotic.

How much Glucomannan do I need to take to feel the benefits?

Because Glucomannan is the most highly viscous soluble fiber known^3,4, when taken as a food supplement, a smaller dose is needed than when compared to other dietary fibre food supplements^1,4.

In order to feel the benefit of Glucomannan as a weight loss supplement, at least three grams of Glucomannan is required daily, split into three doses of at least one-gram each^4,6.

Higher doses may be recommended depending on what the Glucomannan supplement is to be used for. 3.6 to 13 grams daily have been recommended for management of type 2 diabetes, insulin-resistance syndrome and dyslipidaemia⁴.

What are the side effects of Glucomannan?

Glucomannan is usually well tolerated^1,4.However some side effects have been reported in some individuals, such as bloating, gas and mild diarrhoea; these have usually been mild symptoms^3,4.

What are the signs of Glucomannan deficiency?

There are no deficiency symptoms, as Glucomannan is not something you can be deficient in.

What are the risks associated and warnings with taking Glucomannan?

In the past there have been some cases reported of obstruction of the oesophagus after ingestion of Glucomannan tablets or chewable jellies⁴. This is likely because the Glucomannan absorbed water before it reached the stomach, causing it to swell and obstruct the throat resulting in choking. This is no longer an issue now that it is available only as a cellulose capsule or powder to be mixed with water, as the capsule protects the powder until it reaches the stomach⁴. It’s important to note that for these reasons Glucomannan capsules should be swallowed whole, do not open them.

Other than this, Glucomannan has very few adverse events associated with it, it is usually considered safe^1,4.However, there is also a possibility that it could affect the bioavailability of other drugs³, as discussed further below.

What is a good Glucomannan supplement?

Feel Glucomannan is a good Glucomannan supplement. The product is 100% plant-based and made in the UK. Each capsule contains 500mg of Glucomannan (Konjac fibre).

Where can I buy Glucomannan?

Glucomannan is a food supplement and so it can be purchased from health food stores, online retailers such as Feel.

Glucomannan and Chromium

Chromium is a mineral that can help to regulate insulin¹¹ - the hormone that is released when our blood sugar levels rise, metabolising carbohydrates and sugar into fat storage. It’s therefore a potentially useful supplement to take for weight loss.

A recent pilot study published in the Journal of Functional Foods investigated the use of Glucomannan supplements taken in conjunction with chromium and oligofructose (a dietary prebiotic fibre) and a calorie-controlled controlled diet, by women who were overweight or obese¹¹. They found that the participants had a significant reduction in body weight, waist and hip circumference, and body fat percentage, as well as a significant reduction in systolic blood pressure. They also found that the women improved their mood and reduced cravings for savoury foods while participating in the study and were found to have improved levels of healthy gut bacteria.

Interactions and contradictions when taking Glucomannan Supplements

Because of Glucomannan’s bulking and viscosity effects, there is a possibility that it could reduce the absorption of prescription drugs taken orally^4,12. You should therefore take any oral drugs 1 hour before or 4 hours after Glucomannan⁴ and seek medical advice from your health care provider before taking Glucomannan supplements.

In particular, because Glucomannan has been found to lower blood glucose levels, it’s advised not to take it alongside medications or other supplements that also have a hypoglycaemic effect⁴.

Glucomannan can also affect the absorption of fat-soluble vitamins¹³. That’s because it has an impact on bile acids which are required for the absorption of fat-soluble vitamins¹³ - vitamins A, E, D and K. Water soluble vitamins (vitamin C and B vitamins) are not affected¹³. Therefore, as with prescription drugs, if you take a multivitamin supplement or any of the fat-soluble vitamins in supplement form, we suggest you take these at a different time of day from your Glucomannan supplement.

References

1.https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3892933/
2.https://pubmed.ncbi.nlm.nih.gov/30586587/
3.https://pubmed.ncbi.nlm.nih.gov/14983741/
4.https://pubmed.ncbi.nlm.nih.gov/16320857/
5.https://www.sciencedirect.com/science/article/pii/S0899900706003133
6.https://doi.org/10.2903%2Fj.efsa.2010.1798
7.https://pubmed.ncbi.nlm.nih.gov/18842808/
8.https://pubmed.ncbi.nlm.nih.gov/12569112/
9.https://pubmed.ncbi.nlm.nih.gov/18041436/
10.https://pubmed.ncbi.nlm.nih.gov/10372241/
11.https://www.sciencedirect.com/science/article/pii/S1756464620303819
12.https://pubmed.ncbi.nlm.nih.gov/6299917/
12.https://pubmed.ncbi.nlm.nih.gov/6096987/