Konjac

botanical

What is it

Konjac (Amorphophallus konjac), also known as elephant yam or devil's tongue, is a flowering plant native to East Asia whose corm (underground stem) is the source of glucomannan, a viscous dietary fiber. Konjac flour is used in traditional Asian cuisine to make jelly, noodles (shirataki), and tofu-like products.

How it works

Konjac's primary bioactive is glucomannan, a soluble polysaccharide that absorbs many times its weight in water to form a viscous gel. This gel slows gastric emptying, promotes satiety, reduces carbohydrate and fat absorption, and binds bile acids in the intestine, lowering cholesterol. Research suggests konjac glucomannan modulates post-meal blood glucose responses by slowing carbohydrate absorption from the small intestine. It also acts as a prebiotic, with partial fermentation in the colon producing short-chain fatty acids that support colon health. Konjac is essentially calorie-free as a food ingredient because its glucomannan content is largely indigestible. This property has made konjac foods (shirataki noodles, konjac jelly) popular in low-calorie and ketogenic diets. The European Food Safety Authority has approved a weight management claim for konjac glucomannan at 3 grams per day.

Evidence for 5 uses

AI-assisted evidence assessment — talk to your doctor before relying on any single supplement.

Weight management

Grade B

Good evidence

Konjac glucomannan at 3 grams per day produces modest weight loss in calorie-restricted diets. Effects are well established and recognized in EFSA health claims.

Cholesterol reduction

Grade B

Good evidence

Konjac glucomannan reduces total and LDL cholesterol by clinically meaningful amounts in randomized trials.

Blood glucose control

Grade B

Good evidence

Reduces post-meal blood glucose spikes and modestly improves HbA1c in type 2 diabetes.

Constipation

Grade C

Moderate evidence

Adds bulk to stool and improves bowel movement frequency. Works similarly to other soluble fibers.

Low-calorie meal replacement

Grade C

Moderate evidence

Konjac-based foods like shirataki noodles provide volume and satiety with minimal calories, supporting calorie-controlled diets.

4 commercial forms

Konjac glucomannan supplement (capsule or powder)

Concentrated glucomannan; requires careful use with water.

Used at 3 grams per day for weight management per EFSA. Take with a full glass of water before meals.

Shirataki noodles

Whole-food source; lower glucomannan concentration but easy to incorporate into meals.

Calorie-free noodles made primarily from konjac glucomannan and water. Popular in low-calorie cooking.

Konjac jelly

Food product; some forms have been banned due to choking risk in children.

Asian dessert and snack made from konjac flour. Read product labels for serving and safety guidance.

Konjac flour

Culinary ingredient for thickening and gel formation.

Used to make noodles, jellies, and other low-calorie foods.

Dosage

For weight management, the EFSA-approved dose is 3 grams of glucomannan per day in three 1-gram doses with water before meals. For cholesterol or glucose management, doses up to 15 grams per day have been used. Konjac noodles and other food forms can be eaten freely with normal caloric considerations.

When and how to take it

Take konjac glucomannan supplements 30 minutes before meals with at least 8 oz of water. Drink additional water afterward. Never take just before bedtime or while lying down. Konjac foods like shirataki can be enjoyed at any time as part of meals.

Food sources

Food	Amount	%DV
Shirataki noodles (1 cup)	approx 2-3 grams glucomannan	—
Konjac jelly (1 serving)	approx 1-2 grams glucomannan	—
Konjac tofu (1 cup)	approx 2 grams glucomannan	—

Safety

Konjac is safe as a food when properly prepared. Glucomannan supplements carry a risk of choking and esophageal/intestinal obstruction if taken with inadequate water or in tablet form. The FDA has banned konjac jelly products that pose choking hazards. Other side effects include bloating, gas, and diarrhea.

Who should be cautious

Avoid in people with esophageal narrowing, swallowing difficulties, or gastrointestinal motility disorders. Use cautiously in children due to choking risk. Diabetics on glucose-lowering medications should monitor blood sugar. Always sit upright while consuming and drink ample water with each dose.

Interactions

Konjac glucomannan can reduce the absorption of oral medications taken at the same time due to its bulk and viscosity. Separate from medications by 1 hour after or 4 hours before. May enhance blood-glucose-lowering effects of diabetes medications. May produce additive cholesterol-lowering effects with statins or other lipid-lowering drugs.

Frequently asked questions

What is konjac used for?⌄

Konjac is used as a low-calorie food ingredient (shirataki noodles, konjac jelly) and as a dietary fiber supplement for weight management, cholesterol reduction, and blood glucose control.

Are shirataki noodles healthy?⌄

Shirataki noodles are very low in calories and provide soluble fiber that supports satiety, glucose control, and cholesterol management. They are a useful tool in calorie-controlled diets.

Can konjac help me lose weight?⌄

Konjac glucomannan supplements at 3 grams per day before meals have demonstrated modest weight loss benefits in calorie-restricted diets. Konjac foods like shirataki also support satiety with few calories.

Is konjac safe to eat daily?⌄

Yes, konjac foods are safe for daily consumption. Glucomannan supplements should be taken with care and ample water to avoid choking or obstruction risk.

Does konjac taste like anything?⌄

Konjac itself is essentially flavorless and odorless, taking on the flavor of whatever it is cooked with. This neutrality makes it versatile in cooking.

References

EFSA: Konjac Glucomannan Health Claim — European Food Safety Authority link
Wikidata: Konjac — Wikidata link

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Disclaimer: These statements have not been evaluated by the FDA. This page is educational, not a substitute for personalized medical advice. Evidence grades are AI-assisted assessments — talk to your doctor before starting any new supplement, especially if you're pregnant, breastfeeding, on medications, or managing a chronic condition.