This Dr. Axe content is medically reviewed or fact checked to ensure factually accurate information.
With strict editorial sourcing guidelines, we only link to academic research institutions, reputable media sites and, when research is available, medically peer-reviewed studies. Note that the numbers in parentheses (1, 2, etc.) are clickable links to these studies.
The information in our articles is NOT intended to replace a one-on-one relationship with a qualified health care professional and is not intended as medical advice.
This article is based on scientific evidence, written by experts and fact checked by our trained editorial staff. Note that the numbers in parentheses (1, 2, etc.) are clickable links to medically peer-reviewed studies.
Our team includes licensed nutritionists and dietitians, certified health education specialists, as well as certified strength and conditioning specialists, personal trainers and corrective exercise specialists. Our team aims to be not only thorough with its research, but also objective and unbiased.
The information in our articles is NOT intended to replace a one-on-one relationship with a qualified health care professional and is not intended as medical advice.
Glucomannan: A Super Fiber for Weight Loss & More?!
August 17, 2017
In recent decades, glucomannan has been introduced to the United States and European markets as a food additive and dietary supplement. What is glucomannan? It’s a beneficial, soluble and fermentable dietary fiber derived from the root of the konjac plant, which is native to Asia.
People in East Asia have used konjac fiber, also known as glucomannan powder, for thousands of years as both food and traditional medicine. The indigenous people of China have used konjac to treat asthma, breast pain, coughs, hernias, burns and various skin disorders. Fast-forward to present day and scientific studies have revealed that supplementing with konjac glucomannan can significantly lower plasma cholesterol, improve carbohydrate metabolism, encourage bowel movements and promote a healthy colon. (1)
One of the reasons some people may be familiar with glucomannan is because it’s marketed for its ability to promote weight loss. Search for “glucomannan Walmart” and you’ll see that chains like Walmart are already selling this plant fiber as a supplement. There is even a brand-name dietary supplement called Lipozene with glucomannan as its primary ingredient.
Glucomannan weight loss just might be possible if you also lead a generally healthy lifestyle, but it’s important to choose the right product and take it in a safe manner. The fiber from konjac root also holds many other surprising health benefits. There are not many glucomannan side effects, but the most dangerous one (choking) is possible yet avoidable. Pretty much tasteless, glucomannan powder can be added to smoothies and be used to make a high-fiber pasta. If you’re not using it already, let’s talk about why you may or may not want to become a consumer of this Asian plant fiber.
5 Glucomannan Health Benefits
1. Weight Loss
Konjac root’s fiber has a very low calorie content but is very high in fiber. Similar to many vegetables, this is a combination that promotes a healthy waist line. Of course, the rest of your diet has to be healthy, and you also need to be exercising regularly. Consuming konjac powder can help weight loss by promoting a feeling of fullness or satiety, which makes you less likely to overeat.
In a 2005 study, 176 healthy overweight people were randomly assigned to ingest either a fiber supplement or a placebo while on a calorie-restricted diet. The fiber supplements were either glucomannan, glucomannan and guar gum, or glucomannan along with guar gum and alginate. All of the subjects consumed a balanced 1,200-calorie diet plus either the fiber supplement or a placebo. After a five-week observation period, the researchers found that all of the fiber supplements plus controlled diet led to a decrease in weight compared to placebo plus diet. However, they conclude that glucomannan specifically produced a reduction in body weight in overweight yet otherwise healthy subjects, but the addition of guar gum and alginate did not seem to cause any additional loss of weight. (2)
Conversely, some studies, like a 2012 one published in the Journal of the American College of Nutrition, did not show that taking glucomannan led to any statistically significant weight loss. (3) However, I think it’s safe to say that glucomannan can likely be effective for promoting weight loss when it’s combined with an overall weight-reducing lifestyle, including a healthy diet and regular exercise.
2. Natural Prebiotic
Probiotic foods are certainly essential for gut health and overall well-being, but prebiotics are what actually help “feed” probiotics. Prebiotics — like glucomannan as well as garlic, jicama and artichokes — are types of non-digestible fiber compound. Glucomannan, like all prebiotics, passes through the upper part of the gastrointestinal tract and remains undigested because the human body can’t fully break it down. But once prebiotics reach the colon, where they’re fermented by the gut microflora, they create probiotics.
Konjac root powder is a prebiotic that feeds the friendly bacteria in the intestine. A study published in 2008 demonstrated that glucomannan supplementation increases the fecal concentration of probiotics in general as well as specific probiotics like bifidobacteria and lactobacilli. (4)
Why is this important? Higher intakes of prebiotics are linked to benefits, including: (5)
- lower risk for cardiovascular disease
- healthier cholesterol levels
- better gut health
- improved digestion
- lower stress response
- better hormonal balance
- higher immune function
- lower risk for obesity and weight gain
- lower inflammation and autoimmune reactions
The fact that konjac root is a prebiotic is one of the reasons why it has the next benefit.
3. Constipation Relief
Constipation is a common problem typically caused by a low-fiber diet, dehydration and lack of exercise. Several studies have demonstrated that glucomannan may be helpful for constipation. When consumed, the powder works as a prebiotic in your system, which is very helpful for promoting healthy bowel movements.
Glucomannan is considered a bulk-forming natural laxative, which means that the intake of it is able to promote a larger, bulkier stool that more easily passes through the colon. It also encourages a stool that requires less straining to expel.
A preliminary trial and a number of double-blind trials found glucomannan to be an effective constipation treatment. For constipated individuals, glucomannan and other bulk-forming laxatives typically encourage a bowel movement within 12 to 24 hours of intake. Studies have shown three to four grams to be effective for constipation. (6)
One 2008 study specifically found that a modest dose of a konjac glucomannan supplement encouraged bowel movements in constipated adults by 30 percent and improved colonic ecology in general. (7)
4. Lowers Cholesterol
A systemic analysis of 14 glucomannan studies was published in the American Journal of Clinical Nutrition, and it revealed that the use of glucomannan had significantly beneficial effects on total cholesterol, LDL cholesterol, triglycerides, as well as body weight and fasting blood glucose. However, it did not affect HDL cholesterol or blood pressure.
More specifically, glucomannan was able to do the following in these studies: (8)
- Lower total cholesterol by 19.3 mg/dL
- Lower LDL cholesterol by 16 mg/dL
- Lower triglycerides by 11.1 mg/dL
- Lower fasting blood sugar by 7.4 mg/dL
How in the world does glucomannan help the body lower these important measures of health? Being the fiber-centric substance it is, it’s able to decrease absorption of cholesterol in the gut by sponging up water in the digestive tract, which reduces the absorption cholesterol by the body. You then have less cholesterol floating around in your blood.
5. Helps Diabetics
There are more than 20 scientific studies involving glucomannan and diabetes. One of the ways it can help diabetics is because it delays the stomach’s natural emptying process, which leads to more gradual sugar absorption and lower blood sugar levels after meals.
A study published in Diabetes Care was small (only 11 hyperlipidemic and hypertensive type 2 diabetics), but it showed very positive effects of konjac fiber. The study subjects, who were being treated conventionally with a low-fat diet and drug therapy, were given biscuits enriched with konjac fiber. Overall, the researchers concluded that the addition of konjac fiber to conventional treatment may improve blood sugar control, blood lipid profile as well as systolic blood pressure in high-risk diabetic patients. In turn, they believe konjac fiber can improve the effectiveness of conventional type 2 diabetes treatment. (9)
Another study gave 72 type II diabetic subjects konjac food for 65 days. Overall, it was concluded that konjac food is very useful in the prevention and treatment of hyperglycemia. (10) Hyperglycemia or high blood sugar commonly affects diabetics. It’s a condition in which an excessive amount of glucose (sugar) circulates in the blood.
Overall, taking glucomannan by mouth or including it in your diet may help to reduce cholesterol, blood sugar levels and blood pressure in people with diabetes, which is why it should be part of a healthy diabetic diet plan.
How to Find Glucommanan Dosage Info
For medicinal purposes, glucommanan powder, capsules or tablets can be purchased at your local health store or online. I recommend entirely avoiding capsule and tablet options, which have both been linked to serious digestive obstructions. Tablets have been known to swell before reaching the stomach. There have also been anecdotal reports of internal bleeding after taking glucomannan pills. (11)
When choosing a powder or flour, you want to make sure that it’s 100 percent pure with no additives or fillers. Organic versions are great idea too but can be harder to find. Eating shirataki noodles or using glucomannan powder to make homemade noodles can be a great, safe way to incorporate glucomannan into your diet. Japanese shirataki noodles are the most famous glucomannan food product. Adding the powder to a shake or smoothie is also another great idea. Again, I recommend staying away from glucomannan pills.
The recommended dosage of glucomannan is lower compared to other fiber supplements because it expands so greatly in water (up to 50 times its weight). One study specifically showed that at doses of two to four grams per day, glucomannan was well-tolerated and resulted in significant weight loss in overweight and obese individuals. (12) For constipation, three to four grams have been shown to work as an effective laxative.
I highly recommend starting with one very small dose per day. Most powdered products suggest a half level teaspoon (two grams) daily with at least eight ounces of water 30 to 45 minutes before a meal. Make sure to follow directions carefully when taking glucomannan powder. It’s absolutely essential to take the powder with a sufficient amount of water so you don’t risk choking.
Store the flour or powder in a cool, dry place.
Glucomannan Plant Origin and Nutrition Facts
Glucomannan comes from the konjac plant (Amorphophallus konjac), specifically the plant’s root. The plant is native to warm, subtropical to tropical eastern Asia, from Japan and China south to Indonesia. The edible part of the konjac plant is the root or corm, from which glucomannan powder is derived. The konjac corm looks similar to an oval-shaped yam or taro. It’s almost entirely fiber with just a little bit of starch. In order for konjac root to become edible, it’s first dried and then milled into a fine powder. The final product is a dietary fiber called konjac flour, also known as glucomannan powder.
It’s said that dry glucomannan can absorb up to 50 times its weight in water. Chemically speaking, glucomannan is a fiber composed of mannose and glucose. It has the highest viscosity and molecular weight when compared with other dietary fibers. When you put dry glucomannan powder in water, it swells tremendously and turns into a gel, similar to psyllium husk powder. Certain gut flora bacteria like Aerobacter mannaolyticus, Clostridium butyricum and Clostridium beijerinckii are able to help break down glucomannan into disaccharides and eventually to glucose and mannose.
The dried corm of the konjac plant contains around 40 percent glucomannan gum. Konjac is very low calories but very high in fiber. A typical serving of the powder is a half level teaspoon (two grams), which contains about five calories and 2.5 grams of fiber. (13) This amount of fiber fulfills roughly 10 percent of daily fiber requirements.
Glucomannan History and Interesting Facts
Konjac is also known as konjak, konjaku, konnyaku potato, devil’s tongue, voodoo lily, snake palm or elephant yam. It’s grown in many Asian countries, including China, Korea, Taiwan and Japan, as well as southeast Asia.
The konjac plant is highly valued for its large, starchy corms (more commonly referred to as konjac roots), used to create konjac flour and jelly. Corms are technically short, vertical, swollen underground plant stems that serve as storage organs used by some plants to survive winter or other adverse conditions, such as summer drought and heat.
Konjac powder is used as a vegan substitute for gelatin and an ingredient in vegan alternative seafood products.
Konjac glucomannan was first used and studied by the Chinese when its medicinal properties were first described in the Shen Nong Materia Medica during the Western Han Dynasty (206 B.C. to 8 A.D.).
Glucomannan is commonly used in foods, drinks and cosmetics for its gelling properties. It’s gotten some bad press in the recent past due to candies containing konjac that caused a series of choking deaths and near-deaths among children and elderly individuals. Brand names included Fruit Poppers, Jelly Yum and Mini Fruity Gels. The problem with these candies was that although they resembled jello-like products, some of them had a gel that was so strong that only chewing could break down the gel. Consumers are supposed to gently squeeze the gel’s cup, but some consumers sucked the product out with enough force to accidentally lodge it in their windpipes. Health officials said the candy can be almost impossible to dislodge if swallowed whole by small children. (14)
Due to choking hazards, konjac fruit jelly was banned from being imported into the United States by the FDA in 2001. (15)
Lately, konjac sponges are gaining popularity as a skin care accessory in in the United States. They’re gentle and especially great for sensitive skin. (16)
Potential Side Effects, Interactions and Caution with Glucomannan
Glucomannan powder is considered safe when consumed as a food. In medicinal amounts, powder and capsules are likely safe for most healthy adults for up to four months. When used medicinally, minor side effects can include diarrhea, flatulence and bloating. Lipozene side effects can include abdominal discomfort, constipation and diarrhea.
However, solid tablets containing glucomannan can be unsafe for adults and are likely unsafe for children due to the fact that they can sometimes cause throat or intestinal blockages. The risk is especially great if you have any structural abnormalities of the esophagus or gut.
Don’t take glucomannan powder or pills if you have ever had esophageal narrowing or swallowing difficulties.
NEVER take glucomannan products without water. It’s highly possible to choke if you try to swallow it dry. Just think of a balloon blowing up in your mouth and throat, and you’ll understand the danger. ALWAYS take glucomannan with plenty of water.
One of the health benefits of konjac is also one of the common glucomannan side effects. It’s the ability of konjac root’s fiber to lower blood sugar. If you have diabetes and take glucomannan, you should monitor your blood sugar closely since it can lower blood sugar levels. If you’re taking it along with a blood sugar-lowering drug, it may cause your blood sugar to go too low. Speak with your doctor to see if the dose of your diabetes medication might need to be changed to account for the glucomannan. Also due to blood sugar effects, stop using it at least two weeks before any scheduled surgery.
If you’re pregnant or breast-feeding, it’s best to avoid glucomannan products since the safety of taking them under these conditions is still unclear. If you have any medical condition or are taking medication already, consult a doctor before taking glucommanan.
Of course, always keep this powder out of reach of children.
Final Thoughts on Glucomannan
The No. 1 reason people are interested in glucomannan is for its potential ability to shed unwanted pounds. Science shows that it might be able to help with weight loss, but as always, there really is no magical weight loss pill. You need to follow a healthy lifestyle, including a whole foods-based diet and regular exercise, in order to have any additional element help you lose weight. Glucomannan taken in a safe and appropriate manner may help your efforts.
Even if you have no interest in losing weight, konjac powder is a prebiotic that can significantly improve issues with constipation, which is excellent for detoxification and overall health. It also may help to improve high cholesterol and blood sugar management.
If you’re on the fence about this powder as a supplement, I suggest trying Japanese shirataki noodles — aka “miracle noodles.” They’re an easy way to give glucomannan a try and have a high-fiber meal at the same time.