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15 Glucomannan Health Benefits, Risks & Side Effects

Written by Biljana Novkovic, PhD | Last updated:
Medically reviewed by
Jonathan Ritter, PharmD, PhD (Pharmacology) | Written by Biljana Novkovic, PhD | Last updated:

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Glucomannan is a fiber with many beneficial effects. It lowers cholesterol, helps control blood sugar in diabetes, and may even help with weight loss. Surprisingly, it also decreases inflammation, potentially helps with allergies, protects the skin from UV radiation, and may delay aging. Read this article to discover more glucomannan health benefits and why you should take this supplement with care.

What Is Glucomannan?

Glucomannan is a complex sugar and soluble fiber. The most commonly used type is konjac glucomannan, which is taken from the tubers of konjac, a plant native to Asia [1].

It is also extracted from [1]:

  • Eastern white pine
  • Higanbana
  • Lily
  • Orchid
  • Ramie
  • Redwood
  • Suisen

It absorbs water extremely well and has the highest viscosity of any known dietary fiber [2].

A few grams of glucomannan powder can turn a whole glass (eight ounces) of water into a gel.

This fiber has been used in food for thickening and binding, as a fat substitution, and as a preservative [1, 1, 1].

It has gained in popularity as a dietary supplement, mainly due to its potential weight-reducing effects.

Mechanisms of Action

Glucomannan works by:

  • Taking up space in the stomach, making you feel full and eat less
  • Decreasing the amount of hunger hormone ghrelin [3]
  • Decreasing the absorption of nutrients (proteins, fats, and sugars) [4, 1]
  • Removing bile acids [5]
  • Promoting the growth of good bacteria in the gut [6, 7]

Health Benefits of Glucomannan

1) Lowers Cholesterol

Bile acids are made from cholesterol. Glucomannan binds to bile acids and helps remove them from the body. As a result, the body has to convert more cholesterol into bile acids, lowering cholesterol levels [5].

Two meta-analyses, one including 12 studies and the other including 14 studies, showed that this supplement significantly lowered LDL and non-HDL cholesterol types. LDL and non-HDL cholesterol increase the risk of heart disease when elevated [8, 9].

2) Beneficial in Diabetes

Glucomannan causes a more gradual absorption of sugar, which reduces spikes in blood sugar levels [1].

A study of 22 diabetic subjects showed that this fiber helped decrease blood glucose levels and cholesterol [10].

In addition, in two studies, each of 20 diabetic adults, glucomannan taken before a meal decreased the spike in blood sugar levels and decreased appetite by decreasing ghrelin [11, 3].

Similarly, glucomannan-enriched food reduced blood sugar levels in type 2 diabetic patients [12].

In another study of 11 type 2 diabetic patients, this supplement didn’t lower blood sugar, but it lowered total: HDL cholesterol ratio and blood pressure [13].

A study of 34 pregnant women showed that this fiber safely decreased blood glucose levels in both diabetic and non-diabetic patients [14].

3) May Help with Weight Loss

Five studies showed that this supplement can help increase weight loss [15, 16, 17, 18, 19].

However, other studies showed that it did not have a significant impact on weight loss [20, 21, 22].

Glucomannan may help with weight loss in certain groups of people but doesn’t seem to have an effect on others. Hopefully, future studies will explain why this supplement works for some and not others, and show which groups benefit most from glucomannan supplementation.

4) Helps with Constipation

In six studies, this supplement was effective in treating constipation and had no side-effects [23, 24, 25, 6, 7, 26].

However, there is also a study of 72 children, that showed this fiber was not more effective than the placebo in treating constipation [27].

5) Is a Prebiotic

Glucomannan increased the production of beneficial bacteria (lactic acid bacteria and bifidobacteria) in seven constipated subjects and eight healthy adults [6, 7].

A small dose of this fiber also increased the number of beneficial bacteria and the production of short-chain fatty acids (SCFAs) in the gut of mice and rats [28, 29].

6) Is Beneficial in Polycystic Ovary Syndrome

PCOS (polycystic ovary syndrome) can cause insulin resistance. A study of 30 women with PCOS showed that this supplement was efficient in reducing their glucose and insulin levels [30].

7) Helps Lower Thyroid Hormones in Hyperthyroid Patients

In a study with 48 hyperthyroid patients, those who received glucomannan, in addition to standard therapy, had significantly lower thyroid hormone levels during the first weeks of treatment [31].

8) May Help Combat Acne

Glucomannan and probiotic bacteria blocked the growth of acne-causing bacteria in a cell study [32].

9) May Decrease Inflammation

This supplement decreased inflammation in rats with arthritis [33].

It also decreased gut and skin inflammation in mice [34, 35].

In these studies, glucomannan decreased Th2 response (IL-4 and IL-13).

10) May Help with Allergies

This supplement prevented allergic rhinitis and dermatitis (nose and skin allergies) in mice [36, 37].

It did so by decreasing IgE levels [38, 39].

11) Promotes Antioxidant Activity

This supplement increased antioxidant and antioxidant enzyme levels in mice and rats [40, 41, 42].

12) May Protect Skin from UV radiation

Glucomannan decreased UV-induced skin redness in human volunteers and protected skin cells against UVB-induced damage [43].

13) May Delay Aging

Long-term feeding with this supplement delays aging in mice and rats [44, 45].

14) Reduces Cholesterol

In a with 120 people with high cholesterol, glucomannan combined with policosanol or chromium-polynicotinate was effective in reducing total and LDL cholesterol but didn’t affect HDL or triglyceride levels [46].

In another trial, 2.4 g/day of chitosan and glucomannan reduced total, LDL, and HDL cholesterol but not triglycerides in 21 overweight people [47].

15) Protects the Skin from UV

A 0.5% glucomannan emulsion applied on skin decreased UV-induced skin injuries in people [43].

Side Effects & Precautions

This fiber has been recognized as safe by the FDA since 1994 and since 1996, it’s been approved as a binder in the food industry [48, 1].

Side effects may include flatulence, stomach pain, and gut obstruction [2, 49].

To prevent it from expanding prematurely and blocking the gut, make sure you take enough water or other liquids. Also, don’t take it immediately before going to bed.

Glucomannan may, in addition, interfere with the bioavailability of ingested drugs [2, 49]. Therefore, you should avoid taking it along with other medication.

This supplement lowers blood glucose. Mixed with diabetic medication, it can cause low blood sugar [1].



Studies usually administer 1 to 5 grams, 1 to 3 times a day with water, 1h before a meal [16, 17, 18, 9, 24].

User Reviews

Users say glucomannan is good for:

  • Controlling blood sugar levels
  • Weight loss
  • Hunger control
  • Constipation
  • Lowering cholesterol
  • Insulin resistance in PCOS

However, some also report:

  • Dizziness
  • Nausea
  • Bloating and gas


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About the Author

Biljana Novkovic

Biljana received her PhD from Hokkaido University.
Before joining SelfHacked, she was a research scientist with extensive field and laboratory experience. She spent 4 years reviewing the scientific literature on supplements, lab tests and other areas of health sciences. She is passionate about releasing the most accurate science & health information available on topics, and she's meticulous when writing and reviewing articles to make sure the science is sound. She believes that SelfHacked has the best science that is also layperson-friendly on the web.

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