What is glucomannan, from which plant is it derived, what does the European Food Safety Authority (EFSA) say about it, and why this fiber must always be consumed with a sufficient amount of water.
You will often find glucomannan in the ingredients of fiber supplements, and in stores as konjac noodles or rice. It stands out for one property: it absorbs an extraordinary amount of water. This is exactly why it is talked about so much, and precisely why one must be cautious with it.
In this article, we rely on EFSA scientific opinions, European Union legislation, and European Medicines Agency (EMA) documents. You will find the sources at the end of the article, and they are marked in the text with numbers, for example [1]. If fiber is new to you, start with our guide “Fiber: what is it and where is it found?”.
What is glucomannan?
Glucomannan is a soluble dietary fiber derived from the tubers of the konjac plant (lat. Amorphophallus konjac). This plant is also known as konjac. EFSA notes that it is mainly grown in Japan and China, and that approximately two-year-old tubers are processed [1]. In East Asia, it has long been used to make traditional dishes, such as jelly and noodles.
Chemically, glucomannan is a polysaccharide, i.e., a long chain of sugars. It consists of mannose and glucose units in a ratio of approximately 1.6 : 1, linked by β(1→4) bonds [1]. The chains are very long: the average molecular weight of konjac glucomannan ranges from 500,000 to 2,000,000 [1]. Human digestive enzymes do not break down such bonds, so glucomannan remains undigested in the small intestine. EFSA notes that it is significantly fermented by the gut microbiota [1].
Why is it called by several names?
- Glucomannan is the name of the fiber itself.
- Konjac is the name of the plant, which you will often see on products.
- Amorphophallus konjac is the scientific name of the plant, which you will find in product ingredients.
- E 425 is the food additive number for konjac. It denotes konjac gum (E 425 i) and konjac glucomannan (E 425 ii) [1].
How much water can glucomannan absorb?
Glucomannan is one of the most water-absorbent dietary fibers. EFSA states that, depending on purity, konjac materials can absorb up to 200 times their weight in water [1]. For comparison, the EMA writes about psyllium that its husks absorb up to 40 times their weight in water [7].
| Fiber | Water absorption capacity compared to its own weight | Source |
|---|---|---|
| Glucomannan (konjac) | up to 200 times, depending on purity | [1] |
| Psyllium husks | up to 40 times | [7] |
When mixed with liquid, glucomannan swells and forms a thick, viscous gel. This is the source of both its popularity and the primary safety rule: it must swell in the stomach, not in the throat or esophagus. We write more about this below.
- Konjac noodles and rice. In these, the gel is already swollen with water.
- Thickener. Therefore, in the food industry, konjac is also used as the food additive E 425 [1].
- Supplements daily fiber intake. EFSA indicates that 25 g of fiber per day is a sufficient amount for the normal functioning of the adult intestine [10].
What do EFSA and EU law say about glucomannan?
In the European Union, only health claims that have been evaluated by EFSA and approved by the European Commission can be used for food products and supplements. EFSA has published two scientific opinions on glucomannan: in 2009 regarding blood cholesterol levels [3] and in 2010 regarding body weight [2]. Based on these, two authorized claims have been included in Commission Regulation (EU) No 432/2012 [4].
Most importantly, both claims have strict conditions of use. A claim can only be used when the product provides the specified amount of glucomannan, and the consumer must be informed about how much to consume and how to use it to achieve the described effect [4].
| Claim area | Required glucomannan amount | Conditions | Source |
|---|---|---|---|
| Normal blood cholesterol levels | 4 g per day | Product must provide 4 g of glucomannan per day; EFSA indicated that it can be consumed in one or more servings | [3, 4] |
| Body weight, when following an energy-restricted diet | 3 g per day | 1 g of glucomannan per quantified portion; three portions per day before meals, each with 1–2 glasses of water; only in conjunction with an energy-restricted diet | [2, 4] |
| For both claims | Not applicable | Mandatory warning about the risk of choking for people with swallowing difficulties or when consumed with insufficient liquid, and advice to drink with plenty of water to ensure the substance reaches the stomach | [4] |
In other words, these claims are not a general property of glucomannan that can be attributed to any product containing konjac. They apply only when the product serving contains the specified amount and all conditions are met.
Important: this data is about glucomannan and EU legal requirements in general. It is not a description of the effects of the fruttberry product. Our mixture contains less glucomannan per serving than these conditions require, therefore we do not use these claims about our product.
Glucomannan safety
Glucomannan is considered a safe food ingredient, but its property of rapid swelling requires attention. Several points are highlighted in EU documents.
Choking risk
The 2017 EFSA assessment recalls that severe adverse events have been reported, such as esophageal obstruction, when the additive was consumed in tablet form and washed down with insufficient liquid [1]. Therefore, Regulation (EU) No 432/2012 requires that a warning about choking risk and advice to drink with a large amount of water accompany glucomannan claims [4].
Why did the EU ban konjac in jelly candies?
EFSA recalls that EU restrictions were introduced following fatal choking incidents after consuming small jelly candies in cups (so-called jelly mini-cups) [1]. A small, dense, and elastic piece of jelly can get stuck in the throat.
- 2003. Directive 2003/52/EC banned the use of konjac (E 425) in jelly confectionery due to the risk of choking [1].
- 2004. By Commission Decision 2004/374/EC, the placing on the market and import of jelly mini-cups containing other gel-forming additives (E 400–E 418) were suspended [5]. Konjac is not on this list because it was already banned in jelly confectionery.
- Today. Annex II to the Food Additives Regulation (EC) No 1333/2008 specifies that E 425 cannot be used in jelly confectionery [1, 6].
EFSA re-evaluation of E 425 (2017)
In 2017, EFSA re-evaluated konjac gum and konjac glucomannan as food additives [1]. The main conclusions:
- no numerical acceptable daily intake (ADI) is needed, and at the maximum permitted level of 10 g/kg in food, there are no safety concerns for the general population [1];
- glucomannan is not absorbed intact by the body and is significantly fermented by gut microbiota [1];
- in a study where adults consumed 3,000 mg per day for 12 weeks, some participants felt abdominal discomfort, including diarrhea or constipation [1];
- EFSA agreed with the previous conclusion that the use of the food additive is acceptable provided that total consumption from all sources does not exceed 3 g per day [1].
Water is the most important rule
The regulation regarding the weight claim specifies that each 1 g portion of glucomannan must be taken with 1–2 glasses of water [4]. This shows how much liquid is needed even for a small amount of this fiber. When glucomannan is part of a fiber blend, water is needed for the entire blend: fruttberry recommends mixing one 5 g scoop with 200–250 ml of water and drinking it immediately.
| Safe consumption rule | Why it is important |
|---|---|
| Drink a sufficient amount of water with each serving | To ensure the fiber reaches the stomach and does not swell in the esophagus [4] |
| Drink the mixed beverage immediately | Fibers swell quickly and the drink thickens |
| Do not consume if you have difficulty swallowing | Such individuals have a higher risk of choking [4] |
| Do not take tablets or capsules without liquid | Cases of esophageal obstruction have been reported when taken with too little liquid [1] |
| Do not take just before sleep | This is EMA advice for taking psyllium, which also swells strongly [8] |
| Start with a small amount and increase gradually | Larger amounts cause abdominal discomfort for some [1] |
| Take medications separately | Swelling fibers can affect medication absorption; in the case of psyllium, EMA specifies a gap of at least ½–1 hour, and for safety, we advise a 2-hour gap [8] |
Also, consult your doctor or pharmacist if you take medications regularly, have diabetes, are pregnant or breastfeeding, have chronic digestive system diseases, or want to give fiber to a child.
Glucomannan, psyllium, and inulin: what is the difference?
All three fibers are soluble, but each has its own characteristics. Therefore, they are often combined in mixtures.
| Fiber | Source | Water absorption | Intestinal fermentation | Main feature |
|---|---|---|---|---|
| Glucomannan | Konjac tubers | Up to 200 times its weight [1] | Significantly fermented [1] | Forms a very viscous gel; requires a lot of water |
| Psyllium | Psyllium seed husks | Up to 40 times its weight [7] | Limited fermentation [7] | Forms a water-retaining gel [7] |
| Inulin | Chicory, agave | Soluble, does not form a thick gel | Rapid [9] | Rapidly fermented soluble fiber; consuming larger amounts causes more gas [9] |
Interestingly, fibers can complement each other. In a magnetic resonance imaging study involving 19 people with irritable bowel syndrome, inulin consumed together with psyllium caused significantly less gas in the colon than inulin alone (median gas volume 618 vs. 3,145 ml·min) [9].
Important: this research data refers to fibers in general. It is not a description of the effects of the fruttberry product and does not replace a doctor's consultation.
You can find more about each fiber in the articles “Psyllium: what is it and how to use it” and “Soluble and insoluble fiber”.
Glucomannan in the fruttberry fiber blend
Glucomannan is one of the ingredients in the fruttberry +fiber blend. It is present in a smaller amount than psyllium and inulin.
What are the ingredients?
- Psyllium husk is the base of the mixture.
- Agave inulin is a soluble, fermentable fiber.
- Freeze-dried strawberries (12%) and blackcurrants (8%) provide taste and color from real berries, not from flavorings.
- Glucomannan from konjac tubers is another soluble fiber.
How much fiber is in the blend?
| Indicator | Value |
|---|---|
| Fiber content per 100 g of blend | 77 g |
| Fiber per teaspoon (5 g) | approx. 3.86 g |
| Energy value per portion | 11 kcal |
| Water per portion | 200–250 ml |
In an independent study by the KTU Food Institute, our blend sample was found to contain as much as 84.4 g of fiber per 100 g.
Mix one teaspoon with 200–250 ml of water and drink immediately. Start with one teaspoon per day and increase the amount every 3–4 days. The mixture contains no added sugar, gluten, lactose, or preservatives and is suitable for vegans.
The 250 g pack is most convenient for home use, while the 30 portions of 5 g are ideal for work and travel.
All fruttberry dietary fibers in one place.
Frequently asked questions about glucomannan
Are glucomannan and konjac the same thing?
Not quite. Konjac (Amorphophallus konjac) is a plant, while glucomannan is a fiber derived from its tubers [1].
Why must glucomannan be taken with plenty of water?
Because it swells very quickly and can absorb up to 200 times its weight in water [1]. A sufficient amount of liquid helps it safely reach the stomach [4].
Do EU glucomannan claims apply to the fruttberry blend?
No, we do not use these claims about our product. EU-authorized glucomannan claims apply only to products that provide 3 g or 4 g of glucomannan per day and meet other conditions [4]. In our blend, glucomannan is one of several fibers, and its amount is lower.
Why were konjac jelly candies banned?
Due to choking incidents after consuming small jelly candies in cups. Konjac (E 425) cannot be used in jelly confectionery in the EU [1, 6].
Does glucomannan contain calories?
Less than digestible carbohydrates, because it is not digested in the small intestine. It is subsequently fermented by the gut microbiota [1].
Are konjac noodles the same as a glucomannan supplement?
Not quite. In noodles, glucomannan is already swollen with water, whereas in supplements, it is dry and only swells after consumption. Therefore, always mix dry powder with a sufficient amount of liquid.
Sources
- EFSA Panel on Food Additives and Nutrient Sources added to Food (ANS), Mortensen A, Aguilar F, Crebelli R et al. Re-evaluation of konjac gum (E 425 i) and konjac glucomannan (E 425 ii) as food additives. EFSA Journal. 2017;15(6):4864.
- EFSA Panel on Dietetic Products, Nutrition and Allergies. Scientific Opinion on the substantiation of health claims related to konjac mannan (glucomannan) and reduction of body weight, reduction of post-prandial glycaemic responses, maintenance of normal blood glucose concentrations (…) pursuant to Article 13(1) of Regulation (EC) No 1924/2006. EFSA Journal. 2010;8(10):1798.
- EFSA Panel on Dietetic Products, Nutrition and Allergies. Scientific Opinion on the substantiation of health claims related to glucomannan and maintenance of normal blood cholesterol concentrations (ID 836, 1560) pursuant to Article 13(1) of Regulation (EC) No 1924/2006. EFSA Journal. 2009;7(9):1258.
- European Commission. Commission Regulation (EU) No 432/2012 establishing a list of permitted health claims made on foods, other than those referring to the reduction of disease risk and to children’s development and health. Official Journal of the European Union. 2012;L 136:1.
- European Commission. Commission Decision 2004/374/EC of 13 April 2004 suspending the placing on the market and import of jelly mini-cups containing the food additives E 400, E 401, E 402, E 403, E 404, E 405, E 406, E 407, E 407a, E 410, E 412, E 413, E 414, E 415, E 417 and/or E 418. Official Journal of the European Union. 2004;L 118:70–71.
- European Parliament and Council. Regulation (EC) No 1333/2008 on food additives. Official Journal of the European Union. 2008;L 354:16–33.
- European Medicines Agency (EMA), Committee on Herbal Medicinal Products. Assessment report on Plantago ovata Forssk., seminis tegumentum. EMA/HMPC/199775/2012, 2013.
- European Medicines Agency (EMA). Community herbal monograph on Plantago ovata Forssk., seminis tegumentum. EMA/HMPC/199774/2012, 2013.
- Gunn D, Abbas Z, Harris HC et al. Psyllium reduces inulin-induced colonic gas production in IBS: MRI and in vitro fermentation studies. Gut. 2022;71(5):919–927.
- EFSA Panel on Dietetic Products, Nutrition and Allergies. Scientific Opinion on Dietary Reference Values for carbohydrates and dietary fibre. EFSA Journal. 2010;8(3):1462.
The information provided is general in nature and does not replace the consultation of a physician or nutritionist. The scientific data provided relates to fiber in general and is not a description of the properties of any specific product. If you have chronic illnesses, are taking medication, or are pregnant or breastfeeding, consult a healthcare professional before taking food supplements. A food supplement is not a substitute for a varied and balanced diet.
