Glucomannan is a natural, water-soluble dietary fiber extracted from the roots of the elephant yam, also known as konjac. Marketed as an effective weight-loss supplement, it has gained considerable attention. This article offers a detailed examination of the science behind glucomannan and its potential benefits and drawbacks.
What is Glucomannan?
Glucomannan comprises 40% of the dry weight of the elephant yam, which is originally from Southeast Asia. It has a long history of use in herbal mixtures and traditional foods like tofu, noodles, and konjac jelly. In addition to being sold as a dietary supplement, it’s used as a food additive - an emulsifier and thickener denoted with the E-number E425-ii.
Glucomannan is available as a supplement, in drink mixes and is also added to food products, such as pasta and flour. It’s also the main ingredient in shirataki noodles. Glucomannan has an exceptional ability to absorb water and is one of the most viscous dietary fibers known. It absorbs so much liquid that a small amount of glucomannan added to a glass of water turns the entire content into a gel. These unique properties are believed to mediate its effects on weight loss.
How Glucomannan Promotes Weight Loss
Like other soluble fibers, glucomannan is believed to promote weight loss in several ways:
Low in Calories: It’s very low in calories.
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Promotes Satiety: It takes up space in your stomach and promotes a feeling of fullness (satiety), reducing food intake at a subsequent meal.
Delays Stomach Emptying: It delays stomach emptying, contributing to increased satiety.
Reduces Absorption: Like other soluble fibers, it reduces the absorption of protein and fat.
Nourishes Gut Bacteria: It also feeds the friendly bacteria in your intestine, which turn it into short-chain fatty acids like butyrate, shown to protect against fat gain in some animal studies. Feeding your gut bacteria may also have other benefits. Some studies have shown a correlation between altered gut bacteria and body weight.
Glucomannan differs from most other soluble fibers, as it’s exceptionally viscous, making it particularly effective for weight loss.
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Scientific Evidence for Weight Loss
Several randomized controlled trials have studied the effects of glucomannan on weight loss. In the largest study, 176 healthy but overweight people on a calorie-restricted diet were randomly assigned either a glucomannan supplement or a placebo. Three different glucomannan supplements with varying dosages were tested. Some also contained other fibers. After 5 weeks, weight loss was significantly greater among those who supplemented with glucomannan.
Several other studies agree with these results. Glucomannan caused modest weight loss in overweight and obese individuals when regularly ingested before a meal. It’s particularly effective when combined with a weight-reducing diet. The same applies to all weight-loss methods - they work best in combination.
Additional Health Benefits
In addition to promoting weight loss, glucomannan may improve some heart disease risk factors. According to a systematic review of 14 studies, glucomannan can lower:
- Total cholesterol by 19 mg/dL (0.5 mmol/L).
- “Bad” LDL cholesterol by 16 mg/dL (0.4 mmol/L).
- Triglycerides by 11 mg/dL (0.12 mmol/L).
- Fasting blood sugar by 7.4 mg/dL (0.4 mmol/L).
According to this research, adding glucomannan to your diet could potentially lower your risk of developing heart disease and type 2 diabetes. As a water-soluble fiber, glucomannan has also been successfully used to treat constipation.
A meta-analysis evaluating the impact of glucomannan supplementation on serum/plasma levels of total cholesterol (TC), low-density lipoprotein cholesterol (LDL-C), triglyceride (TG), high-density lipoprotein cholesterol (HDL-C), Apo B1, Apo A1, APO-B/ A1 ratio, and LDL-C/ HDL-C in adults, showed that glucomannan supplementation decreased TC, LDL-C, and Apo-B, while it had no significant effect on TG, Apo-B/A1, LDL-C/HDL-C, and APO-A1. Moreover, it significantly decreased HDL-C levels.
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Recommended Dosage and Safety
For weight loss, a dosage of 1 gram, 3 times per day is considered sufficient. Mixed with water, glucomannan expands and can absorb up to 50 times its weight. Therefore, the recommended dosage of glucomannan is lower compared to other fiber supplements. Glucomannan does not have any effect on weight loss unless it is taken before a meal. Timing recommendations range from 15 minutes to 1 hour before a meal.
Glucomannan is well tolerated and generally considered safe. However, if glucomannan expands before reaching the stomach, it may cause choking or blockage of the throat and esophagus, the tube that moves food from your mouth to your stomach. To prevent this, it should be washed down with 1-2 glasses of water or another liquid. Some people may experience mild side effects, such as bloating, flatulence, soft stools or diarrhea, but these negative effects are uncommon. Glucomannan can also reduce the absorption of oral medications like sulfonylurea, a diabetes drug. This can be avoided by taking the medication at least four hours after or one hour before ingesting glucomannan.
Potential Drawbacks and Side Effects
While common side effects are usually mild, some people may experience gut-related issues like bloating, flatulence, diarrhea, and stomach pain. These symptoms typically subside as the body adjusts, but they can be more pronounced if too much is taken or if it's not consumed correctly.
It’s crucial to take glucomannan with plenty of water-at least one to two full glasses. This allows it to reach the stomach before expanding into a gel. Without enough water, there’s a risk it may swell too early, potentially leading to choking or blockages in the throat or digestive tract. In fact, due to this risk, glucomannan in tablet or dry powder form has been banned or restricted in some countries, including Australia and parts of the EU.
Taking too much glucomannan can increase the risk of digestive blockages and may interfere with the absorption of medications or nutrients. There isn’t enough evidence to recommend glucomannan for children, pregnant or breastfeeding women. And do check in with your doctor before taking glucomannan if you’re using any medications that affect blood sugar.
How to Maximize Glucomannan's Effectiveness
The general advice on the recommended glucomannan dosage for weight loss is to take 1g three times per day, around one hour before a meal. It’s best to take glucomannan alongside a healthy diet and regular exercise. Studies note that the beneficial effects of glucomannan may be enhanced via diet-namely, eating fewer calories than you burn each day.
Research Findings and Contradictions
A study by Walsh DE, et al. evaluated the safety and efficacy of glucomannan for achieving weight loss in overweight and moderately obese individuals consuming self-selected diets. Participants were randomly assigned to take 1.33 grams of glucomannan or identically looking placebo capsules with 236.6 mL (8 ounces) of water one hour before breakfast, lunch, and dinner for 8 weeks. The primary efficacy outcome was change in body weight after 8 weeks. Other efficacy outcomes were changes in body composition, hunger/fullness, and lipid and glucose concentrations. Safety outcomes included gastrointestinal symptoms/tolerance and serum liver enzymes and creatinine levels.
A total of 53 participants (18-65 years of age; BMI 25-35 kg/m2) were enrolled and randomized. The two groups did not differ with respect to baseline characteristics and compliance with the study supplement. At 8 weeks, there was no significant difference between the glucomannan and placebo groups in amount of weight loss (−.40 ± .06 and −.43 ± .07, resp.) or other efficacy outcomes or in any of the safety outcomes. Glucomannan supplements administered over 8 weeks were well tolerated but did not promote weight loss or significantly alter body composition, hunger/fullness, or lipid and glucose parameters.
The study enrolled only healthy overweight and moderately obese individuals consuming self-selected diets and maintaining usual physical activity levels. As noted by Sood et al., the beneficial effects of glucomannan on weight loss may be enhanced by dietary modifications, such as hypocaloric diets. The lack of body composition changes may be due to the absence of an exercise intervention as part of the study design. The study also found no changes in plasma lipid or glucose concentrations, possibly because it enrolled only healthy individuals and excluded those with dyslipidemia or elevated serum glucose.
Irregular eating patterns also may provide an explanation for the results. Rather than eating 3 meals, many participants reported that they “grazed” throughout the day and ate the majority of their calories in the evening, possibly circumventing the dosing schedule of 2 capsules one hour before breakfast, lunch, and dinner. Similarly, irregular eating patterns may explain the lack of difference in hunger and fullness sensations between the two groups. While the dosage (3.99 g/day) of glucomannan used in our study was similar to or at the lower range of those used in other studies, a higher dosage of glucomannan should be tested in future studies.
Glucomannan Complex
Glucomannan Complex is a nutritional supplement for weight loss. One time purchase of a bottle starts from £24.00. It often combines glucomannan with other ingredients for a compounded effect. For instance, glucomannan and chromium-which can help keep blood sugar under control-are often combined. Voy’s Glucomannan Complex capsules bring these ingredients together with green tea, offering a convenient supplement option.
Alternatives to Glucomannan
With weight loss supplements, we know that a big part of their appeal is how convenient they are to take. But there are plenty of other options worth knowing about, too-like weight loss medicines which have been studied in more detail. There are also injections, like Wegovy and Mounjaro, that can lead to losses of up to 25% of your starting weight. Or there’s orlistat, a pill that can support over 10% weight loss in some people.
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