Glucomannan
OTHER NAME(S): glucomannan, konjac mannan
Overview
Glucomannan is a type of soluble fiber that comes from konjac root. It is available over the counter as a dietary supplement. It is used to improve digestive and metabolic health. Common side effects include constipation, diarrhea, bloating, and gas. Before taking glucomannan, make sure to tell your health care provider about any health conditions you have or medicines you are taking. If you are taking glucomannan tablets, it is important to drink a full glass of fluid with each dose.
Uses
What is glucomannan used for?
Glucomannan is commonly used to improve metabolic and digestive health. Its benefits for other uses are not well defined.
Note: The FDA has not reviewed glucomannan for safety and effectiveness. Learn more about dietary supplements here.
How does glucomannan work (mechanism of action)?
Glucomannan is a type of soluble fiber that comes from the roots of the konjac plant (Amorphophallus konjac). Dietary supplements that contain glucomannan are made from these roots. Some foods that are made from konjac, such as shirataki noodles, contain large amounts of glucomannan.
Soluble fiber, whether from foods or supplements, can help keep bowel movements regular. It can also act like a prebiotic, which means that it can increase the growth of healthy bacteria in your gut and slow down the growth of bad bacteria. As a soluble fiber, glucomannan may be used to improve digestive health and help manage constipation and diarrhea. But it is not clear how much glucomannan is needed to help with digestive health, and it is not expected to help with severe constipation or diarrhea.
Soluble fibers may reduce how much cholesterol you absorb from the foods you eat, which may help lower cholesterol levels after a meal. They may also make you feel more full during and after a meal, which may help reduce how much you eat. But glucomannan does not seem to help with weight loss, and any changes in cholesterol levels are likely to be small. Regardless, soluble fiber is considered an important and healthy part of the diet. Learn more about dietary fibers here.
How should I store glucomannan?
You should store glucomannan according to the product label. Most dietary supplements should be kept in a cool, dry location that is out of the reach of children and pets and not in direct sunlight.
Side Effects
What are the most common side effects of glucomannan?
The most common side effects of glucomannan are listed below. These side effects may vary depending on the dose you are taking or the specific product you are using. Tell your health care provider if you have any of these side effects that bother you.
- Bloating or gas
- Constipation or diarrhea
There may be other side effects of glucomannan that are not listed here. Contact your health care provider if you think you are having a side effect of a supplement. In the U.S., you can report side effects to the FDA at www.safetyreporting.hhs.gov or by calling 888-SAFEFOOD (888-723-3366). In Canada, you can report side effects to Health Canada at www.health.gc.ca/medeffect or by calling 866-234-2345.
What are the serious side effects of glucomannan?
While less common, the most serious side effects of glucomannan are described below, along with what to do if they happen.
Severe Allergic Reactions. Glucomannan may cause allergic reactions, which can be serious. Stop taking glucomannan and get help right away if you have any of the following symptoms of a serious allergic reaction.
- Breathing problems or wheezing
- Racing heart
- Fever or general ill feeling
- Swollen lymph nodes
- Swelling of the face, lips, mouth, tongue, or throat
- Trouble swallowing or throat tightness
- Itching or skin rash
- Bumps on the skin called hives that can be red, pink, white, or brown depending on your skin tone
- Nausea or vomiting
- Dizziness, feeling lightheaded, or fainting
- Stomach cramps
- Joint pain
Precautions
Who should not use glucomannan?
Allergies to Ingredients. People who are allergic to any of the following should not take glucomannan.
- Glucomannan
- Any of the ingredients in the specific product
Your pharmacist can tell you all of the ingredients in the specific glucomannan products they stock.
What should I know about glucomannan before using it?
Glucomannan is a dietary supplement. It cannot be marketed to treat or cure a disease.
Read and follow the directions on the specific product you are taking, or take it as recommended by your health care provider.
Keep glucomannan out of the reach of children.
Taking glucomannan with food may help reduce the risk of side effects.
Glucomannan tablets should be taken with a full glass of fluid so that they do not get stuck in your throat (esophagus). If glucomannan tablets get stuck in your throat, they can swell up and block it completely. Taking glucomannan as a powder or capsule can help reduce the risk of this side effect.
If you are taking glucomannan powder, use an appropriate measuring device, such as the device included with the product. Read the label carefully, and mix the powder with the amount of fluid stated on the label.
The FDA has not tested glucomannan products to confirm that they contain the ingredients stated on their labels. Some dietary supplements have been tested by third-party organizations to confirm that they contain the ingredients listed on their labels and do not contain any harmful chemicals. Learn more about how to choose a safe dietary supplement product here.
What should I tell my health care provider before using glucomannan?
Tell your health care provider about all of your health conditions and any prescription or over-the-counter (OTC) medicines, vitamins/minerals, herbal products, and other supplements you are using. This will help them know if glucomannan is right for you.
In particular, make sure that you discuss any of the following.
Gastrointestinal (GI) Conditions or Past GI Surgery.Glucomannan swells up when it absorbs the fluids in your mouth, throat, stomach, and intestines. If you have an abnormal GI tract, there is a rare risk that glucomannan can block (obstruct) your throat, stomach, or intestines. If you have a GI condition that changes the shape of your stomach or intestines or have had GI surgery in the past, speak with a health care provider before taking glucomannan.
Other Medicines and Supplements.Glucomannan may interact with other medicines and supplements. Before taking glucomannan, tell your health care provider about any prescription or over-the-counter (OTC) medicines, vitamins/minerals, herbal products, and other supplements you are using. See the Interactions section for more details.
Pregnancy. It is not known if or how glucomannan could affect pregnancy or harm a fetus. Tell your health care provider if you are pregnant or plan to become pregnant.
Breastfeeding. It is not known if glucomannan passes into breast milk. Tell your health care provider if you are breastfeeding or plan to breastfeed.
Interactions
Does glucomannan interact with foods or drinks?
There are no known interactions between glucomannan and foods or drinks, but taking glucomannan with food may help reduce the risk of side effects.
It is unknown if drinking alcohol will affect glucomannan.
Does glucomannan interact with medicines (drug interactions)?
Always tell your health care provider about any prescription or over-the-counter (OTC) medicines, vitamins/minerals, herbal products, and other supplements you are using.
Glucomannan may affect the absorption of some medicines. Tell your health care provider about all medicines that you take or have recently taken.
The interactions between glucomannan and medicines are not fully understood. As with most dietary supplements, the research on drug interactions with glucomannan is incomplete. Always check with your health care provider before taking glucomannan with any medicines.
Dosing
What should I do if I accidentally use too much glucomannan?
If you or someone else has used too much glucomannan, get medical help right away, call 911, or contact a Poison Control center at 800-222-1222.
Glucomannan is available as a powder, capsule, or tablet. Read the product label closely, and speak with a health care provider about how to take glucomannan safely. Do not take double or extra doses, even if you miss a dose.
References
- Drugs and Lactation Database (LactMed) [Internet]: “Glucomannan.”
- EFSA Journal: “Re‐evaluation of konjac gum (E 425 i) and konjac glucomannan (E 425 ii) as food additives,” “Scientific opinion on the substantiation of health claims related to glucomannan and maintenance of normal blood cholesterol concentrations (ID 836, 1560) pursuant to Article 13(1) of Regulation (EC) No 1924/2006,” “Scientific Opinion on the substantiation of health claims related to konjac mannan (glucomannan) and reduction of body weight, reduction of post-prandial glycaemic responses, maintenance of normal blood glucose concentrations, maintenance of normal (fasting) blood concentrations of triglycerides, maintenance of normal blood cholesterol concentrations, maintenance of normal bowel function and decreasing potentially pathogenic gastro-intestinal microorganisms pursuant to Article 13(1) of Regulation (EC) No 1924/2006.”
- National Institutes of Health Office of Dietary Supplements: “Dietary Supplements for Weight Loss, Fact Sheet for Consumers,” “Dietary Supplements for Weight Loss, Fact Sheet for Health Professionals.”
- FDA: “Questions and Answers on Dietary Fiber.”