What Is Glucomannan? Effects, Dosage, and Side Effects

Glucomannan is a water-soluble dietary fiber with a remarkable ability to absorb water, extracted from the root of the konjac plant (Amorphophallus konjac). Traditionally, konjac has been used primarily in Asian cuisine. Well-known examples include shirataki noodles and konnyaku, a gel-like food that is particularly popular in Japan. Konjac is also known as a plant-based food additive: under the designation E425, it is used as a gelling and thickening agent.

The unique characteristic of glucomannan lies in its exceptional water-binding capacity. When mixed with water, it forms a gel-like mass that can absorb up to approximately 50 times its own weight in water. It is precisely this swelling property that makes glucomannan so interesting.

The most important effect of glucomannan is based on its ability to bind water. When glucomannan is taken with sufficient liquid, it forms a gel-like mass. This expands in the stomach and may therefore contribute to an earlier feeling of fullness.¹

¹Glucomannan contributes to weight loss in the context of an energy-restricted diet. This claim is only valid when 3 g of glucomannan are consumed daily, divided into three servings of 1 g each, taken with 1–2 glasses of water before meals and as part of an energy-restricted diet.

In addition, glucomannan can bind bile acids and cholesterol in the intestine, promoting their excretion. As a result, the body uses cholesterol from the bloodstream to produce new bile acids.²

²Glucomannan contributes to the maintenance of normal blood cholesterol levels. This beneficial effect is obtained with a daily intake of 4 g of glucomannan.

The mechanism is relatively simple: glucomannan binds water, expands, and can therefore create a greater feeling of fullness in the stomach. This may help you feel satiated sooner and thus consume fewer calories.* Nevertheless, glucomannan is not a miracle solution. Its scientifically proven effect on weight loss applies explicitly only in the context of an energy-restricted diet. Without a calorie deficit, a balanced diet, and regular physical activity, no long-term effect can be expected.

*In practice, this means: Follow the approved dosage – 1 g three times daily before the main meals, taken with plenty of water.

Pure glucomannan is a plant-based dietary fiber and is virtually calorie-free. When used correctly and taken with sufficient fluids, it is generally considered well tolerated and is used in numerous food supplements as well as foods such as konjac noodles.

Dietary fiber in general is an important component of a balanced diet. Among other things, it can influence the transit time of food through the stomach and intestines, stool consistency, the frequency of bowel movements, and feelings of fullness. The German Nutrition Society recommends a daily intake of at least 30 g of dietary fiber for adults. However, according to the German National Nutrition Survey II, this recommendation is often not met.

Glucomannan can therefore be a good option for enriching the diet with dietary fiber.

The side effects of glucomannan primarily affect the digestive system. Possible symptoms include bloating, a feeling of fullness, abdominal discomfort, soft stools, diarrhea, or constipation. This may occur because the body first needs to adapt to the increased intake of dietary fiber. In particular, insufficient fluid intake can make stools firmer and worsen these symptoms.

Special caution is required in cases of swallowing difficulties or inadequate fluid intake, as glucomannan can begin to expand before reaching the stomach, potentially creating a risk of choking. People with swallowing difficulties, narrowing of the esophagus, or structural problems of the gastrointestinal tract should therefore not use glucomannan without consulting a healthcare professional.

Caution is also advised when taking medications. Due to its swelling properties, glucomannan may reduce or delay the absorption of orally administered medications and other nutrients in the intestine. As a general guideline, we recommend taking other food supplements or medications 2 hours before or 4 hours after glucomannan. Anyone who regularly takes medication or has pre-existing medical conditions should always discuss the use of glucomannan with their doctor or healthcare provider.

Glucomannan use during pregnancy and breastfeeding should also be discussed with a healthcare professional beforehand.

Experiences with glucomannan vary from person to person. Many users report a greater feeling of fullness, particularly when glucomannan is taken with sufficient water before meals. Others notice little effect, especially if their overall diet is not designed with calorie awareness in mind.

It is therefore important to remember: Glucomannan is not a substitute for a balanced diet and is not a miracle weight-loss solution. Its effectiveness depends largely on correct use, adequate fluid intake, and whether it is consumed as part of an energy-restricted diet.

Glucomannan is most commonly available on the market in the form of capsules, tablets, or powder. Powders should be consumed immediately after mixing, as the fiber may otherwise gel too strongly in the glass. Capsules and tablets should not be chewed or sucked. To make supplementation easier, we chose the capsule form for our product.

For better tolerability, it may be beneficial to start with a lower amount and gradually increase the dosage. This allows the digestive system to adapt to the additional fiber intake. However, one thing remains essential: drink plenty of water.

Glucomannan is a natural, highly swellable dietary fiber derived from the konjac root. The EU-authorized claim regarding weight loss applies only when used at the correct dosage, with adequate fluid intake, and as part of an energy-restricted diet.

Glucomannan may be beneficial for individuals who wish to support their weight-loss efforts. When used correctly, it can serve as a plant-based aid for weight management. However, when used incorrectly—especially with insufficient fluid intake—it may cause adverse effects.

• Health Claims Regulation, accessed on 28.05.2026.
• Panel on Dietetic Products, Nutrition and Allergies (2010): Scientific Opinion on the substantiation of health claims related to konjac mannan (glucomannan) and reduction of body weight (ID 854, 1556, 3725), reduction of post-prandial glycaemic responses (ID 1559), maintenance of normal blood glucose concentrations (ID 835, 3724), maintenance of normal blood cholesterol concentrations (ID 3100, 3217), maintenance of normal bowel function (ID 834, 1557, 3901) and decreasing potentially pathogenic gastro-intestinal microorganisms (ID 1558) pursuant to Article 13(1) of Regulation (EC) No 1924/2006. EFSA Journal 2010;8(10):1798.
• Zusatzstoffe Online: Konjac, accessed on 28.05.2026.
• DGE: Reference values for dietary fibre, accessed on 28.05.2026.