Glucomannan: Usage, Health Benefits & Side Effects

by on |

Glucomannan is a common ingredient in weight loss and fat burner supplements.

You might have read that it is the ingredient responsible for the appetite-suppressant effects of weight loss supplements.

What exactly is glucomannan? How does it work? Is it effective? Should you look for fat loss supplements that contain glucomannan?

In this article, we will review the scientific evidence behind the use of glucomannan for weight loss.

What is Glucomannan?

Konjac glucomannan, more commonly known as only glucomannan is a complex sugar (polysaccharide) that is extracted from the tuber of a spice native to warm and tropical parts of Asia (1, 2).

Its scientific name is Amorphophallus konjac (1). Other names for glucomannan are elephant foot yam, devil’s tongue, and snake palm (2).

In the US and in Europe glucomannan is mostly known only in capsule form or as an ingredient in drink mixes to be used as a supplement, but glucomannan is very well known in East and Southeast Asia for its several ethnic and medicinal uses (3, 8).

The ingredient found in weight loss supplements is glucomannan, which is derived from the konjac root. It is a fiber that has highly viscous properties, meaning that it turns into a gel that cannot be absorbed when it is consumed (4).

The gelling properties of glucomannan have led it to be used for culinary purposes in Japan. It is still used as a food additive because of its thickening and emulsifying qualities. 

However, interest in glucomannan peaked after research showed that it can help to improve weight management, partially block the absorption of fat, reduce appetite, or increase a sense of satiety (the feeling of fullness) (4).

Research also shows that it may help to control cholesterol levels, act as a prebiotic, and have anti-cancer properties (5). We will go into the details behind the research-backed effects of glucomannan in later sections.

How Does it Work?

Glucomannan is a fermentable dietary fiber that is made up of a chain of polysaccharides (complex sugars). The complex sugars are connected by certain bonds that cannot be broken down by our saliva like it can with other sugars (6).

When it can’t be broken down, our body cannot absorb it into our bloodstream, meaning it doesn’t turn into energy like other sugars (6). For this reason, it will sit in the stomach for a while and not be absorbed.

Here, it can absorb up to 50 times its weight in water, becoming a thick gel (6). Additionally, stomach emptying is delayed, making you feel fuller for longer (12).

In other words, glucomannan, when exposed to water, forms a gel and grows up to 50 times its size. As a result, it takes up lots of space in the stomach, making you feel full. But, even though you feel full, glucomannan doesn’t actually contribute to your calories consumed.

So, overall, you’ll eat less, and consume fewer calories. Once it passes the stomach, it moves into the intestine relatively unchanged. Here, “good” stomach bacteria use it as food (a prebiotic) (7).

Evidence shows that prebiotics, like glucomannan, not only promote weight loss, they also help to prevent cancer, reduce cholesterol levels, promote digestive health, and boost the immune system (9). However, to see these benefits, you would need to use glucomannan or other probiotic substances for a long period of time.

Finally, glucomannan, like other soluble fibers, reduces the absorption of proteins and fats, meaning that you will absorb fewer calories (6). Note that the weight-loss effects of glucomannan are best when paired with a low-calorie diet (7).

So, after this review of evidence you can see that glucomannan has the potential to promote weight loss in multiple ways, but is most effective when you take the supplement together with controlling your food intake and/or exercising.

Is it safe?

Most studies have focused on the safety of glucomannan use in the short term, but few have evaluated its safety for use for over more than a few months. Existing studies monitored liver health and blood work and found that glucomannan is safe for use in the short term (7).

However, it is important to note that it may block the absorption of nutrients in the stomach. For this reason, if you have or are at risk of nutrient deficiencies, don’t take glucomannan at every meal.

Most importantly, note that glucomannan is on the FDA’s Generally Recognized as Safe List (10, 11).

Health benefits

Shirataki Noodles
Shirataki noodles – typical Japanese noodles high in glucomannan

Some of the health benefits of using glucomannan or taking supplements that contain glucomannan include:

It’s low in calories

Since most of glucomannan cannot be absorbed, it contributes very little to your energy needs. Most people take glucomannan with the goal of losing weight, so the fact that it is low in calories is important to that end.

It promotes a feeling of fullness

The scientific term for when you feel full is satiety. The two main ways in which glucomannan promotes satiety is by absorbing water and expanding in the stomach making you feel full fairly quickly (6).

Additionally, It sits in the stomach for longer, rather than passing quickly to the intestine. This lengthens the feeling of fullness, helping to fight cravings between meals (12).

It reduces fat and protein absorption

Glucomannan is a soluble fiber, so it helps to reduce the absorption of protein and fat.

This means that even if you consume more fat than what is ideal for your specific weight loss plan, glucomannan will help prevent all of it from being absorbed (13).

It may help to control glucose levels

People with insulin resistance and diabetes have difficulty maintaining healthy glucose levels, leading to sometimes dangerous spikes in their blood sugar. Some evidence shows that taking glucomannan may help to moderate glucose metabolism, thus helping to reduce blood sugar spikes (14).

Is a prebiotic

Glucomannan acts as a probiotic in your intestines, meaning that it feeds friendly bacteria that promote gut health. When it is digested by good bacteria, glucomannan is turned into butyrate, which may help prevent fat gain (15, 16).

Promotes weight loss

Since it is most commonly promoted as a weight-loss supplement, the big question is whether it actually does that.

A clinical study carried out with 176 men and women found that those that took a glucomannan supplement and were on a calorie-restricted diet lost significantly more weight than those who restricted calories and took another form of fiber (17).

However, note that in order to have an effect on weight loss it must be taken before a meal with plenty of water (18).

Side effects

Some rare, but possible, side effects if not taken per the instructions include:

  • Throat blockage, especially if you don’t drink it with enough water.
  • Bloating
  • Flatulence
  • Diarrhea

Usage and Dosing Considerations

If you are taking it for weight loss, you shouldn’t need to take more than 1 gram, three times a day (before meals) (18).

If you are just starting with glucomannan supplementation, try taking it once a day first (maximum 1 gram), and, if you don’t have any side effects, gradually increase the frequency. Remember to take glucomannan with abundant water for safe and effective use.

Risks and Precautions

Glucomannan has been found to interact with some medications. If taken with diabetes medications, it might compound the blood sugar lowering effect (19).

Just like glucomannan absorbs liquids and other substances in the stomach and intestines, it may also absorb any medications you are taking, reducing their effectiveness (19).

Remember that you should always consult your physician before taking on a new supplement regimen.


Is glucomannan an appetite suppressant?

Yes. it expands in your stomach, making you feel full. It also makes your stomach empty more slowly, extending the feeling of fullness. Together, this helps to reduce appetite.

What foods contain glucomannan?

Glucomannan is only naturally found in the konjac root. However, it is also used in processed foods as a thickener and emulsifier.

Does fiber help you lose belly fat?

Most research agrees that non-digestible fiber helps you lose body fat, and may target abdominal fat, specifically. Glucomannan is a source of non-digestible fiber (20).

How can I reduce my stomach fat?

A balanced diet with moderately lower calories than your body requires to maintain your weight and exercise are the safest and most effective ways to lose stomach fat. The effects of diet and exercise can be increased or accelerated with supplements like glucomannan.

Does glucomannan cause gas?

While it is rare, just like all fermentable fibers, glucomannan can cause gas in some people.

Is glucomannan a laxative?

Since glucomannan is a non-digestible fiber, it may cause some people to have more frequent stools. This may be more common in people who don’t regularly eat abundant fiber.


Glucomannan is an ingredient that is often included in weight loss supplements. As we have reviewed above, research shows it has the potential to help you lose weight, boost gut health, and lower blood sugar, among others.

To maximize its weight loss effect, glucomannan should be taken before meals with abundant water and paired with a balanced diet and exercise. Remember that you should always consult with your physician before taking on a new supplement regimen.




Leave a Comment