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Is Glucomannan Safe? (Benefits, Side Effects, Diet Uses)

Michael Garrico
Published by Michael Garrico | Co-Founder & Marketing Director
Fact checked by Donald Christman, BHSc FACT CHECKED
Last updated: May 22, 2023
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As a personal fitness coach, I spend a lot of time working with my clients and their dietitians to come up with weight loss and cutting plans.

And because the diet is such a central part of achieving weight loss goals, I’ve spent a lot of time talking to nutritionists about different natural ingredients like konjac glucomannan that can help with those efforts.

To help you understand what benefits glucomannan supplements do and don’t provide, I gathered up all my research into this post.

Let’s dive right in.

Quick Summary

  • Glucomannan is safe for human consumption and has been approved and listed as a dietary fiber by FDA.
  • This dietary fiber was used to treat cough, asthma, skin disorders, breast pain, and for detoxing.
  • Currently, glucomannan helps reduce LDL cholesterol levels, promote weight loss, reduce blood sugar levels, and reduce total plasma cholesterol.

Is It Safe To Take Glucomannan For Diet Efforts?

stack of white capsules in a spoon

Yes, konjac glucomannan is generally classed as safe for diet efforts, and the FDA has taken steps to declare it a dietary fiber [1].

Now, this doesn’t mean that it is an FDA-approved substance, and dietary supplements like this don’t require such approval.

“Dietary fiber that can be declared on the Nutrition and Supplement Facts labels includes certain naturally occurring fibers that are “intrinsic and intact” in plants and added isolated or synthetic non-digestible soluble and insoluble carbohydrates that the FDA has determined have physiological effects that benefit human health.”

- Sharon Spielman, Writer at

But the FDA generally only considers such labeling decisions when there are only limited or no significant side effects associated with them. And in the case of glucomannan, the known side effects are very limited [2].

I was unable to find any resources that indicated that glucomannan poses significant risks of allergic reactions, so for most people, it most likely won’t cause any issues.

What Is Glucomannan?

Glucomannan is an extract from the konjac plant, and it's basically a viscous dietary fiber. It’s extracted from the root of the konjac plant and has been used for generations in alternative medicine.

Some of the reasons it was used in traditional Chinese medicine were for [3]: 

  • Asthma
  • Cough
  • Detox
  • Breast pain
  • Skin disorders

While this might still be a common reason for some people to use it, we couldn’t find clinical trials that support these benefits.

But because it’s a fiber that turns into a gel in the stomach, it does have some benefits for your digestive system.

Let’s take a closer look.

How Does Glucomannan Work?

fresh konjac plant

Glucomannan works by affecting blood sugar and appetite, among other things.

The Journal of Clinical Nutrition did extensive research into studies that have evaluated the use of glucomannan supplements.

These studies included an assessment of cholesterol levels and weight loss in overweight and obese patients [ 4].

The results of this research showed that regular use of glucomannan helped:

  • Reduce total plasma cholesterol
  • Reduce LDL cholesterol
  • Promote weight loss
  • Reduce blood sugar levels

A further study has revealed that glucomannan is also an appetite suppressant [5]. This would explain why people take it to help with extended fasting periods or avoid snacking between meals.

The result would be a further stabilization of blood sugar and ultimately more successful weight loss efforts.

Related Article: How To Lose Weight Through Nutrition

What Are The Benefits Of Taking Glucomannan?

There are both direct and indirect benefits of taking glucomannan that clinical trials have proven.

First of all, there is a direct impact on low-density lipoprotein cholesterol (LDL), which reduces cardiovascular risk factors [6]. This would then further indirectly impact blood pressure with a better cholesterol profile.

There is also a scientific link to insulin resistance syndrome [7]. This would indicate that it influences your blood glucose level, and a more stable blood sugar plays an important role in maintaining a healthy body weight [8].

The main reason I take it during cutting phases is the effect on my appetite mentioned above [5]. It seems to help me extend my intermittent fasting times more easily.

person holding up one pill from a stack of it

A recommended dosage of glucomannan dietary fiber is 1g, as multiple studies suggest [6].

That seems to be a good starting point if you’re trying to lose weight in a more controlled and sustainable way.

However, other controlled metabolic trial results were also based on doses up to 13g per day [9]. Personally, I think that’s a bit much and could make you feel very bloated.

If you’re starting with a raw powder, then like most viscous dietary fibers, it’s best to start with a small amount of 1g. You can then slowly increase it by spreading the dosage out over the day.

When Should You Take Glucomannan?

You should take glucomannan powder first thing in the morning, which is generally what I recommend my readers and clients take as part of a carbohydrate-restricted diet. This would allow you to eat your breakfast significantly later, e.g., after 10 or 11 am.

Such an intermittent fasting approach has been shown to lead to weight reduction [10].

And if you have been struggling with snacking between your main meals, then taking a small glucomannan capsule or other weight loss supplement would help you bridge those gaps without reaching for a donut or candy bar.

Who Shouldn’t Take A Glucomannan Supplement?

person showing her stomach

People with sensitive stomachs probably shouldn't take glucomannan supplements.

However, because there are limited known side effects of glucomannan, it’s generally safe for healthy adults to take it on a regular basis [2].

For overweight and obese individuals, the question will mainly come down to whether they are suffering from other significant health issues.

If you have a sensitive stomach, then it is possible that it will cause bloating and diarrhea [11].

And there’s one other important thing to keep in mind.

Because glucomannan swells up into a gel when it mixes with your stomach fluid, it might also absorb medication that you take at the same time [12].

So, if you do take oral pills for health issues like blood pressure, make sure you don’t take them at the same time as your glucomannan. Give it at least an hour or more to be on the safe side and talk to your doctor for further advice.

Should You Take It Raw Or As A Dietary Supplement?

If you head to a health food store, you’ll likely find pulverized konjac glucomannan in a tub or in glucomannan capsules. The capsules are convenient as they give you the exact same dosage each time.

The powder gives you a bit more flexibility in each dosage, which might be helpful if you’ve worked out exactly how much you want to take.

The other option is to take glucomannan supplements that also contain other ingredients. There are several fat burner supplements that I’ve successfully tried out that contain a good dose of glucomannan.

And with the added other ingredients, you might be in a position to speed up your weight loss progress.

Fat burner supplements containing glucomannan:


Is Glucomannan Safe for Kidneys?

Yes, glucomannan is safe for kidneys. Research suggests that dietary fiber may also have a protective effect on the kidneys [13].

How Much Weight Can You Lose with Glucomannan?

With a calorie-restricted diet and plenty of exercise, it’s possible to lose 2lbs a week with glucomannan [14]. But how much body weight you lose with glucomannan is entirely dependent on how consistent your diet and exercise efforts are.

Is Glucomannan The Right Option For You?

My own experience and research with a nutritionist have led me to conclude that this is a good weight loss supplement for most people. I regularly take it for intermittent fasting and cutting phases with good success.

It’s not going to significantly alter body composition on its own. But with the right diet and exercise routine, it can make enough of a difference to help you get to your target weight.

The one weight loss supplement that we recommend to readers and clients that contains glucomannan is Instant Knockout. The combination with thermogenic ingredients has given us great results in cutting phases.

But it will also help you if you’ve hit a weight loss plateau and want to extend your fasting times for more calorie restriction. Find out more about it in our Instant Knockout review to see what kind of results we achieved with it.


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