Find out all about glucomannan, including what it does, the benefits to taking it, side effects and how much you might need.
Glucomannan, or konjac as it is sometimes known, is a natural, water-soluble fibre derived from the roots of a south-east Asian plant called the elephant yam.1
It has been traditionally used by the Chinese to detoxify and ease symptoms of asthma, and is still used to make noodles and tofu.2
It is often used as a bulking agent in foods, appearing as E425 on food labels.3 It’s also available as capsules and powder, and is added to some diet foods such as pastas and noodles.
As with any fibre, glucomannan can help you feel more satisfied after eating, but what makes it interesting to scientists is that glucomannan has extraordinary water absorption capacities – it’s able to absorb up to 50 times its own weight in water!4
Now you know what glucomannan is, here are the top 5 potential glucomannan benefits.
Like all soluble fibres, glucomannan is highly absorbent, binding to water to form a gel.5 This helps:6
A 2005 study by Norway’s University of Tromso reported that dieters who took glucomannan lost more weight than those taking other high-fibre supplements.7
However, a 2013 study in Journal of Obesity found it had no effect on weight.8
As a viscous dietary fibre, glucomannan is the favourite food for certain friendly bacteria in our guts.
A 2010 laboratory study by the University of Reading found that it helped encourage healthy levels of gut bacteria populations, for example bifidobacterium, but more research on humans is still needed.9
And like all fibres, glucomannan can reduce constipation by increasing bulk, and speeding up food transit time through the colon.10
According to a 2008 review of evidence in The American Journal of Clinical Nutrition, glucomannan can reduce levels of total cholesterol and cause a drop in ‘bad’ LDL cholesterol, too.
Researchers suggested that glucomannan has this effect by altering both the way cholesterol is produced in the liver and how fats in the body are stored or used for energy.11
Consuming glucomannan when you’re feeling constipated could help to ‘get things moving’ in your gut and help you find relief.
This is thought to be because more fibre in general will help relieve constipation – and glucomannan is an excellent source of that!
One study on 31 children found that supplementing glucomannan was beneficial for treating chronic constipation with no significant side effects. Significantly fewer children complained of abdominal pain, too.12
Another study with pregnant women suggested that supplementing glucomannan could help improve their constipation symptoms. The participants reported that taking glucomannan improved consistency and frequency of stools.13
Glucomannan could help to keep your skin hydrated and healthy.
This is thought to be because glucomannan is a natural probiotic that can act as fuel for our skin’s microbiome and help keep it balanced.
There is limited research on its efficacy, but one 2013 study found that glucomannan may help to improve overall skin health, as well as potentially helping to soothe acne symptoms.14
You have a few choices when it comes to konjac / glucomannan supplements and products, including:
It totally depends on what you like!
Handpicked content: 7 of the best glucomannan supplements
A dose of around 2g to 4g per day has been used safely in studies, but always read the packaging or food label first.15
Take glucomannan 15 minutes to an hour before a meal, and make sure you swallow it with 1-2 glasses of fluid to avoid it expanding before it reaches your stomach, as this could be dangerous.16
Glucomannan has not been proved safe for the following people:
It is generally recommended that you take glucomannan around 15-30 minutes before you eat a meal if you are using it to try and manage your weight.
For other reasons, it shouldn’t really matter when you consume it, but try to avoid taking it too close to bedtime.
Generally, glucomannan is well-tolerated. Mild side-effects can include:18
This is because glucomannan predominantly impacts our gut – and while it may help relieve constipation, it could also swing the other way and cause us to feel these other symptoms.
Just take it slowly with glucomannan and see how your body reacts before taking it regularly.
Glucomannan is considered generally safe for adults, but you should always check with your GP if you have any health conditions before taking it – especially if you are diabetic.
Australia and the European Union banned konjac jellies as it may pose a choking risk, especially in children. This is because it does not dissolve easily and absorbs a lot of water – which is why it is important to chew konjac jelly thoroughly before swallowing.
Now that you're clued up on glucomannan, find out which are the best glucomannan supplements available right now: 7 of the best glucomannan supplements.
Last updated: 24 May 2021
Joined Holland & Barrett: Jan 2018
Bsc in Nutrition, Registered Associate Nutritionist and Certification in Pre and Post Natal Nutrition
Donia started her career as a freelance nutritionist, later she joined Nestle as their Market Nutritionist to help support their healthier product range, before joining the team at Holland & Barrett in January 2018.
Donia has over 6 years experience as a Nutritionist and also works with clients on a one to one basis to support their goals which include weight loss, prenatal and postnatal nutrition and children’s health.