In this article
- Why does konjac have so much fiber in the first place?
- Shirataki noodles by the numbers
- How konjac compares with other high fiber superfoods
- Myth vs fact: are konjac noodles a free swap for pasta?
- What research says glucomannan can do
- A checklist for trying konjac foods
- The caveat that matters most
- Konjac fiber: questions people ask
- Sources
Drop a pinch of konjac fiber into water and it can swell to 80 to 100 times its original volume, according to a 2023 review in Nutrients. Few foods behave anything like it.
That swelling is the short version of why does konjac have so much fiber. The plant stores most of its dry weight as a single soluble fiber, and food makers turn that fiber into noodles, rice and jellies that are mostly water held in a fiber gel.
Why does konjac have so much fiber in the first place?
Konjac is an Asian plant also known as elephant yam, devil’s tongue or voodoo lily, as Cleveland Clinic notes. The part people eat is the corm, a starchy underground bulb that can grow to about 10 inches across.
Starchy foods like potatoes store most of their energy as starch, which your body digests into sugar. Konjac’s corm leans heavily on a different molecule called glucomannan, a long chain of mannose and glucose sugars joined mostly by what chemists call beta-1,4 links.
The 2023 review reports that konjac bulbs are about 50% glucomannan by dry weight, with polysaccharides making up about 70% of the dry matter. Refined konjac powder generally tops 65% glucomannan and can reach about 80% with better processing.
Your body can’t digest glucomannan, which is why the FDA has said it intends to count it as dietary fiber rather than a carbohydrate you burn for energy. When half of a plant’s dry matter is a fiber like that, its products land very high on the fiber scale.
A fiber built to hold water
Glucomannan is soluble fiber, the kind that dissolves in water and forms a gel. In the review, its viscosity was much higher than carrageenan, xanthan gum and gum arabic at the same concentration, and about five times that of guar gum and oat beta-glucan.
That thickness is what lets a little konjac flour set a lot of water into a firm noodle. It’s also why the fiber behaves so strongly in your gut, where it forms a gel with stomach fluids.
How konjac’s fiber stacks up against other soluble fibers
Oat beta-glucan and psyllium husk are two of the best known soluble fibers, and both are already on the FDA’s list of added fibers that count on a label. In the 2023 review, glucomannan’s gel was about five times as thick as oat beta-glucan’s at the same concentration.
That doesn’t make it better in every way. It does explain why such a small amount of konjac flour can change the texture of a whole pot of water.
Shirataki noodles by the numbers
Shirataki, Japanese for “white waterfall,” are the best known konjac food. Cleveland Clinic describes them as roughly 97% water and 3% konjac flour, boiled and shaped into noodles or rice-sized pieces.
A 1 cup serving has about 20 calories, 6 grams of carbohydrate and 6 grams of fiber, which is about 21% of the 28 gram Daily Value. Nearly every carbohydrate gram in the noodle is fiber.
By the FDA’s rule of thumb, 20% or more of the Daily Value counts as high. That puts a cup of shirataki in the high fiber group, a spot few foods reach at 20 calories.
Not sure how much fiber your own day should hold? Our fiber calculator works it out from a few details about you.
Other konjac foods you’ll see
The corm is ground into flour or turned into a gel, and that base shows up in more than noodles. You’ll find konjac shaped into rice-sized pieces, set into jellies and sold as glucomannan capsules or powder.
Fiber per serving varies across these products, so the Nutrition Facts panel is the number to go by. Supplements in particular deliver concentrated glucomannan, which is why the safety advice later in this article matters most for them.
How konjac compares with other high fiber superfoods
Konjac’s real standout is fiber per calorie. Here’s shirataki next to some of the strongest fiber foods in the Dietary Guidelines list:
| Food | Serving | Fiber | Calories | Fiber per 100 calories |
|---|---|---|---|---|
| Shirataki noodles | 1 cup | 6.0 g | 20 | 30.0 g |
| Artichoke, cooked | 1 cup | 9.6 g | 89 | 10.8 g |
| Broccoli, cooked | 1 cup | 5.2 g | 54 | 9.6 g |
| Raspberries | 1 cup | 8.0 g | 64 | 12.5 g |
| Navy beans, cooked | 1/2 cup | 9.6 g | 128 | 7.5 g |
| Chia seeds | 1 tablespoon | 4.1 g | 58 | 7.1 g |
| Bulgur, cooked | 1/2 cup | 4.1 g | 76 | 5.4 g |
Per calorie, shirataki gives you more than twice the fiber of raspberries and about three times that of broccoli. Per serving, though, artichokes and navy beans still deliver more grams.
This is why konjac often shows up on lists of high fiber superfoods. It’s less about volume of nutrients and more about how much fiber you get for almost no energy.
Myth vs fact: are konjac noodles a free swap for pasta?
Myth: Konjac noodles are a zero-calorie stand-in that gives you everything pasta does, minus the carbs.
Fact: They replace the texture, not the nutrition. Cleveland Clinic notes shirataki have no antioxidants, vitamins or minerals of note, and the dietitian it quotes doesn’t recommend eating them every day, mainly so your diet stays varied.
Treat konjac as a fiber-rich base, then build the nutrition on top of it. Vegetables, beans and a protein turn a 20 calorie bowl of noodles into an actual meal.
Here’s one way to build it. Start with 1 cup of shirataki for 6 grams of fiber, then add 1 cup of cooked snow peas for 4.5, 1 cup of cooked mushrooms for 3.4 and half a cup of chickpeas for 6.3.
That bowl comes to about 20.2 grams of fiber for roughly 266 calories, using Dietary Guidelines numbers for the add-ins. The chickpeas also bring protein that the noodles don’t.
Want ideas for stir fries and noodle bowls that pair konjac with vegetables and beans? Our recipe eBooks have high-fiber meals ready to try.
What research says glucomannan can do
Most of the evidence comes from glucomannan supplements rather than konjac foods. The 2023 meta-analysis pooled six randomized trials with 440 adults who had type 2 diabetes, using doses of about 1.2 to 15 grams a day for 3 to 16 weeks.
Compared with control groups, glucomannan lowered fasting blood sugar, blood sugar two hours after meals, fasting insulin, total cholesterol and LDL cholesterol. Body weight, triglycerides, HDL cholesterol and blood pressure didn’t change significantly.
Some control groups got a placebo and others got wheat bran, so glucomannan was sometimes measured against another fiber. The trials tested supplements, and none of them looked at konjac noodles as a regular food.
The authors flagged real limits. The trials were small, published between 1999 and 2007, and run only in Asia and Canada, so longer and larger studies are still needed.
Cleveland Clinic adds that a systematic review found small but significant weight loss in people with overweight or obesity who took glucomannan. The fiber may also act as a prebiotic, food for helpful gut bacteria, and help firm stool.
Regulators have taken notice too. The FDA counts only certain added fibers on the Nutrition Facts label, and in January 2020 it said it intends to add glucomannan to that list.
A checklist for trying konjac foods
- Rinse first. Run shirataki under cold water for a couple of minutes to cut the fishy smell, which comes from a compound called trimethylamine.
- Heat briefly. Dry packaged noodles need about 3 minutes in boiling water, while wet packed noodles are already cooked and only need reheating.
- Dry them in a pan. A quick toss in a dry skillet drives off extra water and firms the texture.
- Start with a small portion. Large amounts at once can bring gas, bloating or diarrhea.
- Drink water. Cleveland Clinic suggests plenty of fluids when you add konjac foods.
- Add color. Toss in cooked broccoli or Brussels sprouts for more fiber plus the vitamins konjac lacks.
Shirataki also contain no wheat, milk or eggs. Cleveland Clinic notes they suit gluten free, keto, low FODMAP and vegan eating patterns.
If your gut is sensitive to sudden fiber changes, our gut health guides walk you through adding fiber at a pace that feels comfortable.
The caveat that matters most
The same swelling that makes konjac a fiber powerhouse can also make it a choking hazard. Glucomannan expands in liquid, and Cleveland Clinic warns that this risk applies to children and adults, especially people with swallowing problems.
In the early 2000s, the FDA issued warnings after konjac fruit jelly candies swelled in some people’s throats. Supplements carry a similar risk, so the dietitian Cleveland Clinic quotes advises taking capsules with a full 8 ounces of water.
Two more groups need extra care. Because konjac can lower blood sugar, people on insulin or other diabetes medicines could see dangerously low levels, and Cleveland Clinic notes that people on anti-obesity drugs may run into severe constipation or other digestive problems.
Konjac fiber: questions people ask
How much fiber is in konjac noodles?
About 6 grams per cup, according to Cleveland Clinic. That’s roughly 21% of the 28 gram Daily Value for about 20 calories.
What kind of fiber is in konjac?
Glucomannan, a soluble fiber that forms a thick gel in water. Konjac bulbs are about 50% glucomannan by dry weight.
Is konjac a superfood?
It’s a standout for fiber per calorie, with shirataki giving about 30 grams of fiber per 100 calories. It lacks notable vitamins and minerals, so pair it with other foods.
Does konjac help with weight loss?
Possibly a little. A systematic review found small but significant weight loss with glucomannan supplements, but a 2023 meta-analysis in type 2 diabetes saw no significant weight change.
Can konjac lower cholesterol?
Glucomannan supplements lowered total and LDL cholesterol in a 2023 meta-analysis of six trials. Most of that evidence comes from supplements rather than konjac noodles.
Is konjac safe to eat?
For most people, in normal food amounts, yes. It can cause gas or bloating in large amounts, and its swelling makes jelly candies and supplements a choking risk.
Is konjac a grain or a vegetable?
It’s closer to a root vegetable. The edible part is the corm, an underground bulb, though konjac noodles and rice are often used like grains or pasta.
Sources
- Zhang Z, Zhang Y, Tao X, Wang Y, Rao B, Shi H. “Effects of Glucomannan Supplementation on Type II Diabetes Mellitus in Humans: A Meta-Analysis.” Nutrients, 2023. pmc.ncbi.nlm.nih.gov
- Cleveland Clinic. “5 Ways Konjac Can Help Boost Your Health.” 2024. health.clevelandclinic.org
- Cleveland Clinic. “4 Reasons To Give Shirataki (Miracle) Noodles a Try.” 2024. health.clevelandclinic.org
- U.S. Food and Drug Administration. “Questions and Answers on Dietary Fiber.” 2024. fda.gov
- U.S. Department of Agriculture and HHS. “Food Sources of Dietary Fiber.” Dietary Guidelines for Americans, 2020 to 2025. dietaryguidelines.gov
- U.S. Food and Drug Administration. “Daily Value on the Nutrition and Supplement Facts Labels.” 2024. fda.gov
