Health Benefits of Glucomannan

Root Extract Used to Treat High Cholesterol and Constipation

Shirataki noodles, peas, asparagus, star-shaped tofu
Westend61 / Getty Images

Glucomannan is a substance extracted from the root of the konjac plant (Amorphophallus konjac) native to Asia. Glucomannan is rich in soluble fiber, the type of fiber that attracts water and helps soften stools.

Long used in traditional Chinese medicine, glucomannan is now sold as a dietary supplement and weight loss aid. The herbal remedy is made from the yam-like tubers of the konjac plant. The tubers, commonly referred to as elephant yams, are used in Japanese kitchens to make yam cakes (konnyaku) and noodles (shirataki).

Konjac is also known as own as devil's tongue, voodoo lily, and snake palm. In traditional Chinese medicine, konjac flour is used to make a herbal medication known as hongqu.

Health Benefits

As a soluble fiber, glucomannan works by building bulk in the intestines. This not only helps relieves constipation, but it can also slow the absorption of sugar and cholesterol from the gut.

In alternative medicine, glucomannan has a long history of use as a "detox aid." Proponents claim that glucomannan can aid in the treatment of allergies, asthma, cough, skin problems, constipation, diabetes, high blood pressure, and high cholesterol.

Glucomannan is also believed to promote weight loss, slow the aging process, and even fight certain forms of cancer. Some of these claims are better supported by research than others. Here is a look at some of the key findings:

High Cholesterol

Glucomannan may help keep cholesterol levels in check, suggests a 2008 review of studies published in the American Journal of Clinical Nutrition.

Based on a review of 14 clinical trials, glucomannan appeared to lower total cholesterol and "bad" low-density lipoprotein (LDL) cholesterol. On the other hand, it did nothing to improve "good" high-density lipoprotein (HDL) cholesterol or blood pressure.

The quality of reviewed studies was moderate to poor. Further research is needed to establish whether glucomannan is a safe and viable treatment option for hyperlipidemia (high cholesterol).


Soluble fiber of any sort can help maintain or improve digestion. Most health authorities recommend a total dietary fiber intake of 25 to 30 grams per day with about one-fourth—6 to 8 grams—coming from soluble fiber.

Glucomannan is a reasonable option, particularly if you have chronic constipation. It also appears to be safe for short-term use in children and pregnant women.

A 2018 study in the Journal of Family Medicine and Primary Care reported that glucomannan was more effective in relieving constipation than magnesium hydroxide (used in Mylanta and Milk of Magnesia) during the third trimester of pregnancy.

Weight Loss

There is some contention as to whether the metabolic effects of glucomannan translate to weight loss. The results of clinical studies have been largely mixed.

A 2005 review of studies published in Alternative Therapies in Health and Medicine concluded that glucomannan supplements, taken in 2- to 4-gram daily doses, increased weight loss in overweight or obese adults. The loss was mainly attributed to premature satiation (the feeling of fullness following the consumption of certain foods).

Recent studies have not drawn similar conclusions.

According to a 2013 study from Rush University, a daily 4-gram dose of glucomannan taken over eight weeks did nothing to promote weight loss or significantly alter body composition, hunger/satiation, or cholesterol or blood sugar levels.


Contrary to popular belief, glucomannan has less impact on blood sugar levels than expected. This is surprising given that glucomannan passes through the intestines largely intact and can absorb up to 50 times its weight in water.

While it would fair to assume that this would slow the absorption of sugar (glucose) in the digestive tract, most research has shown that this doesn't occur.

According to the 2013 study from Rush University, an eight-week course of glucomannan actually led to a slight increase in fasting blood glucose compared to placebo.

Among study participants, any individual reversals were attributed to weight loss rather than the effects of glucomannan itself.

Other studies have shown that taking glucomannan supplements before a meal may provide a transient drop in blood glucose but had no demonstrable effect on insulin or HbA1c levels.

Possible Side Effects

Glucomannan supplements are generally considered safe if taken as prescribed but are intended only for short-term use only. Little is known about their long-term safety. Common side effects include flatulence, diarrhea, belching, bloating, and stomach upset.

Because glucomannan can absorb 50 times its weight in water, it is important that you take it with no less than 8 ounces of water. Swallowing the supplement "dry" can lead to choking or the blockage of the esophagus or intestines.

Although glucomannan is unlikely to affect your anti-cholesterol or anti-diabetes medications, it's important to speak with your doctor if you are on these drugs and intend to use glucomannan.

Even though they are presumed safe, never use glucomannan in children or during pregnancy without first speaking with your pediatrician or OB/GYN.

Dosage and Preparation

Glucomannan powders, capsules, and tablets are widely available online and sold in many natural food stores and shops specializing in dietary supplements. Most are formulated in doses ranging from 500 to 2,000 milligrams.

There are no guidelines directing the appropriate use of glucomannan supplements. Depending on the aims of treatment, dosages of up to 9 grams (9,000 milligrams) per day, divided into three to four doses, are considered safe. Always be sure to take each dose with at least 8 ounces (250 milliliters) of water.

For children, doses should not exceed 100 milligrams per kilogram per day (mg/kg/day). Work with your pediatrician to calculate the correct dosage.

What to Look For

Dietary supplements are largely unregulated in the United States and can vary significantly from one brand to the next. To ensure quality and safety, opt for supplements that have been tested by an independent certifying body like the U.S. Pharmacopeia (USP), ConsumerLab, or NSF International.

Also, keep an eye out for brands that have been certified organic under the regulations of the U.S. Department of Agriculture. This will ensure greater purity and safety.

Most importantly, try not to be swayed by health claims that may or may not be true. In the past, manufacturers like Vitacost, PediaLean, Herbal Worldwide Holdings, BioTrim, and Obesity Research Institute have been charged by U.S. Food and Drug Administration (FDA) or Federal Trade Commission (FTC) with making false claims about glucomannan supplements.

Other Questions

What are the best food sources of glucomannan?

Glucomannan is found in high concentrations in shirataki noodles, a type of gelatinous noodle with almost no calories or carbohydrates. Shirataki are often used as a pasta substitute in low-carb diets and take well to stir-frying and soups.

If you want to go straight to the source, you may be able to find konjac root in larger Asian grocery stores. It has a taro-like flavor and a slippery mouth sensation when eaten. Konjac root is most commonly used to make traditional Japanese dishes like oden (a type of fish cake) and nikujyaga (a slow-cooked meat stew).

Also known as elephant yam, konjac root should not be confused with Japanese yam (Dioscorea japonica).

Was this page helpful?
6 Sources
Verywell Fit uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. Sood N, Baker W, Coleman C. Effect of glucomannan on plasma lipid and glucose concentrations, body weight, and blood pressure: Systematic review and meta-analysis. Am J Clin Nutr. 2008;88(4):1167-1175. doi:10.1093/ajcn/88.4.1167

  2. National Institutes of Health. Dietary Reference Intakes (DRIs): Recommended Dietary Allowances and Adequate Intakes, Total Water and Macronutrients.

  3. Janani F, Changaee F. The effect of glucomannan on pregnancy constipationJ Family Med Prim Care. 2018;7(5):903‐906. doi:10.4103/jfmpc.jfmpc_168_18

  4. Keithley J, Swanson B, Mikolaitis S. Safety and Efficacy of Glucomannan for Weight Loss in Overweight and Moderately Obese Adults. J Obes. 2013;2013:610908. doi:10.1155/2013/610908

  5. Keithley J, Swanson B. Glucomannan and obesity: A critical reviewAltern Ther Health Med. 2005;11(6):30‐34.

  6. McCarty MF. Glucomannan minimizes the postprandial insulin surge: a potential adjuvant for hepatothermic therapy. Med Hypotheses. 2002;58(6):487-490. doi:10.1054/mehy.2001.1457