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Heard of glucomannan or konjac flour and want to know what it actually is? We’ve got the expert, fact-based guide to glucomannan
Summary
1Glucomannan for gut health
Glucomannan supports gut health by promoting beneficial bacteria, producing appetite-regulating short-chain fatty acids and easing constipation.
2Glucomannan and heart health
Glucomannan may support heart health by helping maintain normal cholesterol levels and potentially lowering LDL cholesterol.
3Glucomannan and blood sugar
Glucomannan may aid blood sugar management by slowing carbohydrate absorption, supporting fullness and promoting metabolic health.
If glucomannan is on your radar, you may be wondering if it can help with weight loss. Made from konjac flour – yes, the same konjac that is also used for your konjac cleansing sponge – glucomannan is a functional fibre with unique properties that may benefit your health.
So, what exactly is glucomannan and is there any science behind using glucomannan for weight loss? We talked to Karine Patel, registered dietitian and founder of Dietitian Fit, to find out.
What is glucomannan?
Glucomannan is a natural, water-soluble fibre derived from the roots of a South-East Asian plant called the konjac plant (or elephant yam). While glucomannan and konjac flour are often used to mean the same thing, strictly speaking konjac flour is the raw, ground-up powder of the root while glucomannan is the purified, active compound extracted from the root.
Glucomannan has been used in China for over 2,000 years as a traditional medicine for numerous conditions and in traditional foods such as noodles and tofu. These days, glucomannan is available as a supplement in capsules and powder and is added to some diet foods such as very low-carb pastas and noodles. It is also used to bulk up foods – you’ll see it as E425 on food labels.1
A lot of the attention around glucomannan is down to its unique water absorption capabilities – just a small amount of glucomannan will turn a glass of water into a gel.
What are the benefits of glucomannan?
Many of the benefits of glucomannan come from this unique ability to expand so dramatically when it absorbs water. “As it’s a fibre that expands and forms a gel when mixed with water, it can increase levels of fullness and therefore possibly reduce appetite,” says Karine.
Glucomannan may also have other benefits beyond weight loss, says Karine. “Some research has also shown it may support with reducing cholesterol levels and regulating blood sugar, as well as supporting gut bacteria.”2
Let’s take a look at the benefits of glucomannan in more detail:
Glucomannan for weight loss
Glucomannan has been shown to support weight loss when taken before meals, with water, as part of an energy-restricted diet.
- One 2024 trial found that adults with certain obesity-related genetic variants lost more weight when taking a blend of fibres including glucomannan, inulin and psyllium, alongside lifestyle changes, than those taking a placebo. However, because the intervention combined several fibres, the effect cannot be attributed to glucomannan alone3
- A 2025 systematic review4 of 10 randomised controlled trials concluded that konjac glucomannan supplementation was frequently associated with reductions in body weight, BMI and waist circumference in people with overweight or obesity, particularly when combined with calorie restriction. However, the review reported substantial variation in dose and protocol across studies
- Perhaps most significantly, the European Food Safety Authority has approved health claims for glucomannan and weight loss but only when 3g per day is taken in three 1g doses before meals with one to two glasses of water, as part of an energy-restricted diet
“Glucomannan can support with reduced feelings of hunger, but it needs to be combined with a reduction in overall calorie intake, whilst eating healthy and nutritious meals,” says Karine.
Glucomannan for gut health
Interestingly, recent studies have shifted focus from just ‘fullness’ to how glucomannan changes your gut bacteria.
Glucomannan acts as a prebiotic that increases short-chain fatty acids (SCFAs). These signal to the brain to lower appetite and improve insulin sensitivity. This means glucomannan may influence metabolic processes (how your body converts food into energy and regulates blood sugar, fat storage and appetite) via the gut microbiome.”4
Glucomannan specifically promotes the growth of good gut bacteria and is a gentle, effective way to support chronic constipation without the cramping that stimulant laxatives can cause.6-8
Glucomannan and heart health
Looking after your cholesterol is an important part of supporting long-term heart health – and this is where glucomannan may lend a helping hand. This is because glucomannan contributes to the maintenance of normal blood cholesterol levels when consumed as part of a healthy, balanced diet.
Some research also suggests it may help to lower LDL (‘bad’ cholesterol), particularly when taken regularly. This is thought to be down to its gel-forming fibre, which can bind to substances in the gut and help reduce the amount of cholesterol absorbed into the bloodstream. While results can vary, adding glucomannan-rich foods or supplements to a balanced, fibre-rich diet may support your overall heart health.
Glucomannan and blood sugar
Glucomannan may help to support blood sugar management, although the evidence is still emerging. It’s thought to work by slowing gastric emptying and the absorption of carbohydrates, which can lead to a more gradual rise in blood glucose levels after eating. It’s thought to work in a few key ways:
- the gel it forms in the stomach can slow the digestion and absorption of carbohydrates, helping to support a more gradual rise in blood glucose levels after eating
- by slowing gastric emptying, glucomannan may help you feel fuller for longer and support more stable energy levels throughout the day
- as a fermentable fibre, it’s broken down by gut bacteria in the large intestine to produce short-chain fatty acids (SCFAs), which are believed to play a role in metabolic health, including insulin sensitivity 2,9,10
While these effects are promising, glucomannan isn’t a replacement for medical treatment. If you have diabetes or concerns about your blood sugar levels, it’s important to speak to a healthcare professional before making any changes to your diet or supplement routine.
Is glucomannan effective for weight loss?
Glucomannan can support weight loss, but as already mentioned, this is only when taken at a dose of 3g per day, split into three 1g servings before meals with one to two glasses of water, as part of an energy-restricted diet.11
An active lifestyle is important too. “On its own, glucomannan is not a quick fix and should not be used purely as a weight loss supplement,” says Karine.
“Remember that weight loss supplements are not magic solutions – so anything that promises you a quick result by just taking a supplement is most likely a marketing strategy,” says Karine. “For weight loss to be maintained safely long term, you need to look at overall nutrition quality and calories consumed alongside behavioural and habit change.”
Is glucomannan safe?
Glucomannan expands once you take it, so there are specific rules for using it safely. “Take 1g, 30 minutes before a meal, mixed in with a glass or two of water,” says Karine. “Do not take it dry, as the water helps with absorption. If you don’t drink enough water, the fibre can expand in your throat or oesophagus before reaching your stomach, which can pose a choking risk if not taken with enough fluid."
This is true whether you take it as a powder or capsule. When glucomannan absorbs water, it forms a gel, which can slow down how your body absorbs medicine. “Speak to your doctor if you have any medical conditions such as diabetes, before starting to include glucomannan in your diet,” says Karine.
This is true whether you take it as a powder or capsule. When glucomannan absorbs water, it forms a gel, which can slow down how your body absorbs medicine. “Speak to your doctor if you have any medical conditions such as diabetes, before starting to include glucomannan in your diet,” says Karine.
Who can take glucomannan?
Glucomannan is considered safe for most fit and healthy people, as long as it is taken with 1-2 glasses of water. However, you should talk to your GP before using it, especially if you’re on any oral medications, as it can reduce their absorption.12
If you are taking oral medicines, it should be taken at least four hours after or one hour before taking glucomannan – or as your health professional advises you. Your needs could differ based on what you’re taking and why, as well as any underlying conditions.
As glucomannan expands so much, there’s a risk of it blocking the gut or oesophagus. It therefore shouldn’t be taken by people who have structural abnormalities (such as unusual shapes or injuries) in these organs.
It isn’t recommended for pregnant or breastfeeding women, due to a lack of studies.
The final say
There are no quick fixes for weight loss but glucomannan can help when taken correctly alongside a calorie-restricted diet. It may also have other benefits, including gut health and support with blood sugar levels.
Glucomannan FAQs
People use konjac glucomannan as a weight loss aid as it’s a soluble fibre that expands in the stomach and helps you feel fuller. That’s because glucomannan has unique water-absorbing properties, absorbing up to 50 times its weight in water to form a gel.
While generally well tolerated, glucomannan should be avoided by people with problems swallowing, blockages in their gut or oesophagus, or structural gastrointestinal issues. This is because it can cause choking or obstructions as it expands. It is also not recommended for pregnant or breastfeeding women, or children or people on diabetes medication without medical supervision.
It is recommended to take glucomannan 15 minutes to an hour before eating if you want to harness the weight management benefits.
Because of the risk of choking or developing a blockage in the throat, gut or oesophagus, you should take glucomannan at least two to three hours before you go to bed.
Disclaimer – Always read the label and follow guidance when taking glucomannan-cased products. This article provides informational advice and is not a substitute for medical care. Working with experts for accuracy, we take great care to ensure the information is up-to-date and relevant. However, you should always consult your GP or healthcare professional before using supplements or alternative products, particularly if you have medical conditions or are under supervision.
1. EFSA Panel on Food Additives and Nutrient Sources added to Food (ANS), Mortensen A, Aguilar F, Crebelli R, Di Domenico A, Frutos MJ, et al. Re-evaluation of konjac gum (E 425 i) and konjac glucomannan (E 425 ii) as food additives. EFSA J. 2017;15(6):4864. doi:10.2903/j.efsa.2017.4864.
2. EFSA Panel on Nutrition, Novel Foods and Food Allergens (NDA). Oat beta-glucans and reduction of postprandial glucose peak: evaluation of a health claim pursuant to Article 13(5) of Regulation (EC) No 1924/2006. EFSA J. 2026;24(2):9942. doi:10.2903/j.efsa.2026.9942.
3. Pokushalov E, Ponomarenko A, Garcia C, Pak I, Shrainer E, Seryakova M, et al. The impact of glucomannan, inulin, and psyllium supplementation (SolowaysTM) on weight loss in adults with FTO, LEP, LEPR, and MC4R polymorphisms: a randomized, double-blind, placebo-controlled trial. Nutrients. 2024;16(4):557. doi:10.3390/nu16040557.
4. Ghosh A, Mohol P, Ghosh S. Konjac glucomannan as an emerging nutritional strategy for obesity control via gut microbiota and metabolic regulation. Discover Food. 2025;5(1):222. doi:10.1007/s44187-025-00533-0.
5. EFSA Panel on Dietetic Products, Nutrition and Allergies (NDA). 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 (fasting) blood concentrations of triglycerides (ID 3217), 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 J. 2010;8(10):1798. doi:10.2903/j.efsa.2010.1798.
6. Yu Y, Jin S, Yang Y, Han X, Guan R, Zhong H. Interaction between konjac glucomannan and gut microbiota and its impact on health. Biology (Basel). 2025;14(8):923. doi:10.3390/biology14080923.
7. Medicines and Healthcare products Regulatory Agency. Over-the-counter stimulant laxatives: benefit-risk review. London: GOV.UK; 2020.
8. Chen HL, Cheng HC, Wu WT, Liu YJ, Liu SY. Supplementation of konjac glucomannan into a low-fiber Chinese diet promoted bowel movement and improved colonic ecology in constipated adults: a placebo-controlled, diet-controlled trial. J Am Coll Nutr. 2008;27(1):102-8. doi:10.1080/07315724.2008.10719681.
9. Mirzababaei A, Zandkarimi R, Moradi S, Rasaei N, Amini MR, Pourreza S, et al. The effect of glucomannan on fasting and postprandial blood glucose in adults: a systematic review and meta-analysis of randomized controlled trials. J Diabetes Metab Disord. 2022;21:1055-63. doi:10.1007/s40200-022-00993-6.
10. (Insufficient bibliographic data to format accurately from the provided link. DOI: 10.3746/pnf.2025.30.2.120)
11. Kuczora S. Authorised EU health claims for glucomannan, guar gum and hydroxypropyl methylcellulose. In: Foods, Nutrients and Food Ingredients with Authorised EU Health Claims. Cambridge (UK): Woodhead Publishing; 2015. p. 175-188. doi:10.1016/B978-1-78242-382-9.00010-4.
12. Drugs.com. Glucomannan uses, benefits & dosage. 2025 May 21.
