The weight loss space is awash with hundreds of dietary supplements, all promising to help you shed the most weight over the shortest period. But as our experiences show, not many are effective or even safe to use. You may have noticed a relatively new dietary fiber that’s being touted as the "best way to control hunger, suppress appetite, and lose weight." But is glucomannan safe for weight loss?
Here is everything you need to know about glucomannan, its benefits, safety, and side effects.
What Is Glucomannan
Glucomannan is a water-soluble dietary fiber extracted from the tuber or roots of the ‘Amorphophallus konjac,’ or elephant yam – a herb that grows in parts of Asia. Glucomannan makes up to 40% of konjac’s dry weight.
Glucomannan has a long history of use making traditional Asian foods like tofu. This fiber is the main ingredient in noodles sold under ‘Tofu Shirataki’ or ‘zero’ noodles. ‘Zero noodles’ claim to have zero calories, making them appealing to people looking to lose weight.
Glucomannan is also sold as a dietary supplement in tablet forms or as a powder added to food products such as pasta and flour. It’s also sold as a food additive as an emulsifier and thickener.
Glucomannan is a soluble dietary fiber, but it has a few extra qualities that normal fibers don’t have. The main property that sets it aside from other fiber supplements is that it expands when it comes into contact with water.
Glucomannan can absorb water up to 50 times its weight, and because it can expand, its recommended dosage is lower than other fiber supplements. But how does glucomannan work for weight loss?
How Glucomannan Aids Weight Loss
Like other fibers, glucomannan has a few tricks up its sleeve that may aid weight loss, but it's still best to use it in addition to other weight loss therapies, including exercise, a healthy diet, and intermittent fasting.
Also, glucomannan is only effective if it's taken before a meal. Different sources recommend taking it between 15 minutes to an hour before a meal. With that in mind, here is how glucomannan aids weight loss.
1. Takes space in the stomach to reduce food intake
Glucomannan is a renowned thickener and gelling agent. When it comes into contact with water, it expands, absorbing up to 50 times its weight. Consuming glucomannan creates a feeling of satiety by absorbing water in the stomach to create a sticky, bulky fiber.
As the bulky fiber expands, it pushes against the stomach sides, triggering neurons that tell your brain that you are full. This helps regulate your appetite and ensures that you don’t eat much at a subsequent meal, but you still feel full.
2. Reduces the absorption of fats and protein and delays absorption of sugars
Glucomannan's sticky, viscous form also holds on carbohydrates and sugars in the gastrointestinal tract, delaying their absorption into the system. This delay or slowed absorption means there will be less of an insulin spike after meals, which may lower blood sugar levels.
Managing blood sugar and insulin levels may play a part in managing weight.
3. Feeding good gut bacteria
Glucomannan is a fiber, so it positively impacts your gut microbiota. The bacteria in your gut play an essential role in regulating vital bodily functions, including the immune function, metabolism, and now, studies  have linked them to body weight.
According to studies, prebiotic fibers such as Glucomannan help promote the growth of beneficial bacteria in the gut, which may help promote weight loss.
Glucomannan Weight Loss Success Stories
Several studies have examined the effects of glucomannan on weight loss.
In one large study , 176 healthy but overweight men and women were randomized to receive a placebo or three types of fiber supplement combinations – glucomannan, glucomannan and guar gum, or glucomannan, guar gum and alginate.
The subjects were then placed on a restricted 1200 Kcal diet. The researchers noted that glucomannan alone induced bodyweight reduction in healthy overweight people, while the addition of alginate and guar gum didn’t seem to cause any additional weight loss.
Another study  observed the effects of glucomannan fiber in 20 obese subjects for eight weeks. The participants were given either a placebo or 1g glucomannan fiber in 2 capsules with 8 ounces of water 1 hour before each of the three meals per day.
The study found that subjects given glucomannan lost an average of 5.5 pounds without changing their diet or exercise pattern compared to those given a placebo. They also had lower cholesterol, and no adverse reactions were reported.
Another study  involving over 200 overweight or obese patients found that participants who took a glucomannan and psyllium husk mixed dose two to three times a day lost an average of 10 pounds over 16 weeks compared to 1.7 pounds in the placebo group.
How Much Glucomannan Should You Take For Weight Loss?
If you are wondering what the best glucomannan dosage for weight loss is, note that it’s a supplement, and as such, there are no official guidelines on how much you should take. However, the most common dosage used in studies  is 1 gram before each of the three meals per day.
Is Glucomannan Safe For Weight Loss?
With no harsh chemicals or additives, glucomannan fiber supplements are considered pretty safe in adults. It is well-tolerated; although some people may experience mild side effects such as bloating, flatulence, or diarrhea, these adverse effects are however uncommon. If you have known digestive issues, it’s best to check with your registered dietitian, physician, or healthcare provider before using glucomannan.
If glucomannan expands before reaching the stomach, it could become a choking hazard or cause blockage of the esophagus. To prevent this, experts recommend washing it down with a glass or two of water or another liquid.
Glucomannan could also reduce the absorption of prescription drugs. However, this could be overcome by taking the medication one hour before or at least four hours after taking glucomannan. If you take prescription medications, please consult your pharmacist, physician, or healthcare provider before using glucomannan to minimize the risk of drug-nutrient interactions.
- Baer DJ, Rumpler WV, Miles CW, Fahey GC Jr. Dietary fiber decreases the metabolizable energy content and nutrient digestibility of mixed diets fed to humans. J Nutr. 1997 Apr;127(4):579-86. doi: 10.1093/jn/127.4.579. PMID: 9109608.
- Ley RE, Turnbaugh PJ, Klein S, Gordon JI. Microbial ecology: human gut microbes associated with obesity. Nature. 2006 Dec 21;444(7122):1022-3. doi: 10.1038/4441022a. PMID: 17183309.
- Birketvedt GS, Shimshi M, Erling T, Florholmen J. Experiences with three different fiber supplements in weight reduction. Med Sci Monit. 2005 Jan;11(1):PI5-8. PMID: 15614200.
- Walsh DE, Yaghoubian V, Behforooz A. Effect of glucomannan on obese patients: a clinical study. Int J Obes. 1984;8(4):289-93. PMID: 6096282.
- Salas-Salvadó J, Farrés X, Luque X, Narejos S, Borrell M, Basora J, Anguera A, Torres F, Bulló M, Balanza R; Fiber in Obesity-Study Group. Effect of two doses of a mixture of soluble fibres on body weight and metabolic variables in overweight or obese patients: a randomised trial. Br J Nutr. 2008 Jun;99(6):1380-7. doi: 10.1017/S0007114507868528. Epub 2007 Nov 22. PMID: 18031592.
- Keithley J, Swanson B. Glucomannan and obesity: a critical review. Altern Ther Health Med. 2005 Nov-Dec;11(6):30-4. PMID: 16320857.