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Konjac is an East Asian plant, Amorphophallus konjac, grown for its underground tuber, usually sold as konjac root. Its main carbohydrate is glucomannan, a soluble fiber that soaks up water and turns into a thick gel. Ground konjac becomes shirataki noodles and konjac jelly, and purified glucomannan is sold in capsules and powders. That same swelling is why glucomannan labels carry choking warnings and why regulators have acted against some konjac candies and tablets. This guide covers the plant, the fiber, konjac foods, what research has measured and how to read a label.
Peptide Labs sells a glucomannan capsule, which we use as a label example. This article is general information, not medical advice.
Key Takeaways
- Glucomannan is the soluble fiber in konjac root; it holds a great deal of water and becomes very thick.
- Shirataki noodles and konjac jellies are konjac foods; firm mini-cup konjac jellies are blocked from U.S. import as a choking risk.
- Glucomannan must be taken with plenty of liquid; Australia bans glucomannan tablets because they can swell in the throat.
- The EU allows a weight-loss claim only with 3 g a day, water and a calorie-restricted diet; a 2014 meta-analysis found no significant weight loss.
What is konjac?
Konjac belongs to the arum family (Araceae) and is native to East Asia, where it has been eaten for more than a thousand years, according to a 2004 review in Nutrición Hospitalaria. The edible part is a large underground tuber (botanically a corm), which is why products say konjac root. The tuber is dried and milled into konjac flour, and glucomannan is the fiber purified from it.
What is glucomannan?
Glucomannan is a long chain of two sugars, mannose and glucose, joined by bonds that human digestive enzymes cannot break. That makes it a soluble dietary fiber. The same review describes an extraordinarily high water-holding capacity and says glucomannan has the highest molecular weight and viscosity of any known dietary fiber. In practice, a small amount of powder stirred into water becomes a thick gel.
In the U.S., FDA said in January 2020 that it intends to add glucomannan to the regulatory definition of dietary fiber, which affects whether it can be counted as fiber on Nutrition and Supplement Facts labels. For how glucomannan compares with psyllium, inulin and other fibers, see our fiber supplements comparison.
Konjac foods: shirataki noodles and konjac jelly
Konjac shows up in the grocery aisle more often than in the supplement aisle. Shirataki noodles are mostly water with a small share of konjac and are very low in digestible carbohydrate and calories, and konjac flour is used as a gelling agent and gelatin substitute. Konjac jelly is a firmer, chewier cousin of gelatin desserts, and that firmness is the problem with one format.
In 2001 FDA warned about mini-cup gel candies made with konjac after choking deaths and near deaths among children and elderly people. The candies were packaged in small, mouth-sized cups and, unlike gelatin, they keep their shape and do not melt in the mouth. FDA Import Alert 33-15 now allows these mini-cup gel and jelly candies of firm consistency to be detained at the border without examination.
| Konjac form | What it is | Safety note |
|---|---|---|
| Konjac root or flour | Dried, milled tuber | Used as an ingredient; swells a lot in water |
| Shirataki noodles | Noodles made from konjac and water | Chew well; a food, not a supplement |
| Mini-cup konjac jelly candy | Firm, bite-sized gel in a small cup | Under FDA import alert as a choking risk |
| Glucomannan capsules or powder | Purified konjac fiber | Take with plenty of water as the label directs |
| Glucomannan tablets | Compressed fiber tablets | Permanently banned in Australia; can swell in the throat |
Glucomannan supplements and the "take with plenty of water" warning
Glucomannan starts to swell as soon as it meets liquid, including saliva. If a capsule or tablet sticks on the way down, it can expand in the throat or esophagus. Australia has a permanent ban on glucomannan in tablet form for exactly this reason, and European labels must warn that people with swallowing difficulties or who drink too little fluid risk choking, and that it should be taken with plenty of water so it reaches the stomach.
The 2004 review also lists possible downsides: gas, abdominal pain, blockage of the esophagus or lower gut, and a possible change in how other medicines are absorbed. If you take prescription drugs, ask your pharmacist how far apart to take them from a fiber supplement.
- Read the water instruction on the label and follow it every time.
- Skip glucomannan if you have ever had esophageal narrowing or trouble swallowing, as the label we sell advises.
- Keep it away from children; the label we sell says for adults only.
What research on konjac glucomannan and weight has measured
Glucomannan is widely marketed as a weight-loss ingredient because of its bulk, but the evidence is mixed and the regulatory picture differs by region.
- European Union: Glucomannan holds an authorized EU health claim that it contributes to weight loss in the context of an energy-restricted diet. The claim may only be used for products that provide 3 g a day, taken as three 1 g doses with water before meals. That is a regulatory condition of use, not a promise of results.
- 2014 meta-analysis: Researchers at the University of Exeter found 9 eligible randomized trials. Pooling 8 of them showed a difference of 0.22 kg versus placebo, which was not statistically significant. Reported side effects were abdominal discomfort, diarrhea and constipation, and trial reporting quality varied.
- 2013 U.S. trial: 53 overweight or moderately obese adults took glucomannan or placebo capsules with water before meals for 8 weeks while eating their usual diets. The groups did not differ in weight loss, body composition or hunger, and the capsules were well tolerated.
| Source | Design | What it found |
|---|---|---|
| EU health claim (Reg. 432/2012) | Regulatory authorization | Claim allowed only at 3 g a day with a calorie-restricted diet |
| Onakpoya et al., 2014 | Meta-analysis, 9 randomized trials | No statistically significant weight difference vs placebo |
| Keithley et al., 2013 | Randomized trial, 53 adults, 8 weeks | No difference in weight or hunger vs placebo |
The honest summary: glucomannan adds fiber and bulk, and people can feel full after taking it with water, but good-quality trials in U.S. adults eating their normal diets have not shown meaningful weight change on its own.
How to read a glucomannan label
- Amount per capsule and per serving. Capsules are small, so a serving is usually several capsules. Check both numbers.
- Form. Capsules and powders are common in the U.S.; avoid pressed tablets.
- Water instruction. The label should give a minimum amount of liquid per serving.
- Warnings. Look for the choking statement, swallowing-difficulty caution and adults only.
- Other ingredients and allergens, plus any statement about the facility.
Where NOW Glucomannan fits
NOW Glucomannan 575 mg contains glucomannan from konjac root in vegetarian capsules: 575 mg per capsule and 1,725 mg in a 3-capsule serving, with 180 capsules per bottle. The label directs taking each serving with at least 8 oz of water before a meal and warns that without enough liquid it may swell in the throat, causing blockage or choking. It says to avoid use if you have had esophageal narrowing or swallowing difficulties, is for adults only, and advises consulting a physician if pregnant or nursing, taking medication or managing a medical condition.
If you want a fiber that is easier to take as a drink, our psyllium husk guide compares powders, capsules and gummies. You can browse more options in our fiber and gut health category.
Frequently Asked Questions
What is konjac root?
It is the underground tuber of Amorphophallus konjac, an East Asian plant. It is dried and milled into konjac flour, which is used for shirataki noodles and jellies and as the source of glucomannan fiber.
Is glucomannan the same as konjac?
Glucomannan is the main fiber in konjac. Konjac flour contains glucomannan, while glucomannan supplements contain the purified fiber.
Why is konjac jelly a choking hazard?
Firm konjac jelly does not melt in the mouth the way gelatin does. FDA warned about mini-cup konjac candies in 2001 after choking deaths, and they are under an FDA import alert.
Why do glucomannan labels say to take it with water?
Glucomannan swells when it meets liquid. Without enough water it can swell in the throat and cause blockage or choking, so labels require a full glass of water with each serving.
Does glucomannan help with weight loss?
The evidence is mixed. The EU allows a claim only at 3 g a day with a calorie-restricted diet, while a 2014 meta-analysis and a 2013 U.S. trial found no significant weight difference versus placebo.
Are shirataki noodles the same as glucomannan supplements?
No. Shirataki noodles are a food made from konjac and water. Supplements concentrate the fiber into capsules or powder, which is why they carry specific water and choking warnings.
Questions about a label? Contact us or read our Buyer’s Guide. These statements have not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure, or prevent any disease.
Last reviewed September 2026.
Related guides: Psyllium Husk for Weight Loss: Fullness, Evidence, Timing and Safety, Appetite Suppressants: Prescription Drugs, Natural Options and the Risks, Fiber Supplement Side Effects: Gas, Choking Risk, Allergies and Medicine Timing, Why Am I Always Hungry? Everyday Reasons and Medical Causes to Rule Out.