Konjac

Konjac (Amorphophallus konjac)

1. Identity: Botanical Name, Source, and Common Forms

Botanical and Chemical Identity

The scientific name of konjac is Amorphophallus konjac, which belongs to the family Araceae. It is also known by the common names elephant yam and devil's tongue. Konjac is native to warm subtropical and tropical Asia and is widely grown as a cash crop in countries such as China, India, and Japan. The plant is a tropical perennial that grows a single leaf that can reach over a meter across, with a stalk patterned like snakeskin. The part of primary commercial and medicinal interest is the underground corm.

One of the most widely utilised species is Amorphophallus konjac K. Koch ex N.E.Br. (synonym A. rivieri), which has been used in China for thousands of years. In Japan it is called konnyaku, in China jǔruò, and in Korea gonyak.

Key Constituent: Konjac Glucomannan (KGM)

The predominant compound in konjac corms is glucomannan, which accounts for approximately 49–60% of the corm weight. Additionally, corms contain 10–30% starch and 2.6–7% inorganic elements including key minerals such as calcium, aluminum, magnesium, manganese, iron, chromium, and cobalt. These corms also possess crude protein content ranging from 5% to 14%, 3% to 5% soluble sugars, and 3.4–5.3% ash. A small amount of alkaloids (trigonelline) and saponin are present at the stem base.

Konjac glucomannan (KGM) consists of D-mannose and D-glucose residues linked by β-1,4 bonds, with a molar ratio of approximately 1.6:1 or 1.4:1, depending on the genotype. On average, there is an acetyl group on the C-6 position of the backbone per every 9–19 sugar residues, and side chains may exist with a degree of branching of approximately 8%. The molecular weight of KGM ranges from 500,000 to 2,000,000 Daltons, depending on the plant source and processing methods.

KGM exhibits high viscosity, solubility, and swelling properties, as well as good film-forming and gel-forming properties in aqueous solutions. The solubility of KGM in water is attributed to the presence of 5% to 10% acetyl substituent residues on the main chain.

Common Forms and Preparations

Flour extracted from the corm of konjac is used in Far Eastern cuisine to make noodles, tofu, and snacks. It often appears in the form of konjac noodles, konjac tofu, and konjac jelly. Supplemental glucomannan is the concentrated and purified fiber, sold as powder, capsules, and tablets. The historical significance of konjac in Japanese cuisine is particularly notable, where it has been used to produce traditional foods like konnyaku (a gelatinous food made from konjac flour) and shirataki noodles. These foods have been integral components of Japanese cuisine for centuries, appreciated for their unique texture and versatility.

At low concentrations, KGM is capable of forming a strong gel that is approximately 97% water when in the presence of a coagulant, representing one of the lowest energy-density foods available. In Japan, where konjac has a long history of use, it is classified as a traditional food rather than an additive.

2. Traditional and Historical Use

China

The historical significance of konjac is underscored by its first documentation in the Shen Nong Materia Medica during the Western Han Dynasty, which highlights its longstanding role in ancient Chinese medicine. Traditionally, KGM has been utilized in Chinese medicine for over 2,000 years, serving various health purposes such as detoxification, tumor suppression, and treatment of respiratory and skin disorders.

In traditional Chinese medicine (TCM), a gel prepared from the flour has been used for detoxification, tumour-suppression, blood stasis alleviation, and phlegm liquefaction; and for more than 2,000 years it has been consumed by the indigenous people of China for the treatment of asthma, cough, hernia, breast pain, burns, as well as haematological and skin disorders.

Japan and Korea

Over the centuries, konjac has been integrated into various cultural practices, especially in China and Japan, where it has been consumed for its health benefits. This historical context underscores the significance of konjac in both dietary and medicinal practices, highlighting its role as a staple food source in countries like China and Japan. In Japan, the food products konnyaku and shirataki noodles have represented the dominant culinary form of konjac for centuries.

Broader Southeast Asia

The konjac plant grows in Southeast Asia, where dishes made from the root tuber have been valued for around 1,500 years because of their high satiety. Konjac has been used as a culinary ingredient and in herbal medicine for thousands of years in Southeast Asia, China, and Japan.

3. Key Constituents and Mechanisms of Action

Gel Formation and Viscosity

KGM has the highest hydrated volume at the lowest concentration of any dietary fiber. Oral KGM can thus instill a feeling of fullness at a lower dose than other fiber supplements. Glucomannan can absorb up to 50 times its weight in water, forming a viscous gel. This extraordinary water-absorbing property is central to most of KGM's physiological mechanisms.

Satiety and Gastric Mechanisms

Appetite reduction may occur through increasing gastric retention and delaying gastric emptying by the "mass effect" of a gel-like viscous mass forming in the stomach that triggers afferent vagal signals of fullness. Absorption of nutrients in the lumen is slowed and beneficially increases the levels of appetite-related hormones.

Bile Acid Sequestration and Cholesterol Reduction

The gel formed by KGM binds bile acids and cholesterol in the gut, promoting their excretion and thereby reducing circulating LDL cholesterol. The capture of bile acids by glucomannan forces the liver to draw on cholesterol to synthesize new bile acids, thereby reducing cholesterol levels.

Slowing Carbohydrate Absorption

The viscous gel formed by KGM slows absorption of carbohydrates and fats, which helps moderate post-meal blood sugar peaks and fat absorption. KGM may slow the absorption of sugar and cholesterol in the gut, helping to control sugar levels in people with diabetes and reduce cholesterol levels.

Prebiotic and Microbiota Modulation

KGM is degraded by gut microbiota-derived β-mannanase into small-molecule nutrients, which exert diverse physiological regulatory effects. As a prebiotic, KGM modulates gut microbiota composition. Research reveals that depolymerized KGM (DKGM) selectively stimulates Lactobacillus and Bifidobacterium in the colon, cecum, vagina, and skin surface. By blocking their adhesion on mucosal surfaces, DKGM can also restrain the growth of pathogenic bacteria such as coliforms, enterococci, Staphylococcus aureus, Propionibacterium acnes, Clostridium, and Salmonella typhi.

Upon reaching the colon, glucomannan is fermented by the gut microbiota, producing acetate, propionate, and butyrate. These molecules nourish colonic cells (butyrate), modulate insulin release (propionate), and activate FFAR2/FFAR3 receptors involved in appetite regulation.

Anti-inflammatory Mechanisms

Researchers have found that KGM and its derivatives can regulate the polarization of macrophages, inducing their transformation into classically activated M1-type macrophages or alternatively activated M2-type macrophages, and even facilitating the interconversion between M1 and M2 phenotypes. KGM has demonstrated efficacy in reducing pro-inflammatory cytokines such as TNF-α, IL-1β, IL-4, and IL-13, particularly in experimental models of colitis, atopic dermatitis, and skin inflammation. These findings are largely from animal and in vitro models; robust human clinical data confirming these mechanisms remain limited.

4. Scientific Evidence by Area of Use

4.1 Body Weight and Obesity

In 2010, the European Food Safety Authority (EFSA) confirmed that konjac glucomannan is beneficial for weight loss, reducing postprandial blood sugar, and lowering blood cholesterol concentration, and issued a health statement. Specifically, EFSA validated in 2010 the following claim, incorporated into EU Regulation No. 432/2012: "Glucomannan, in the context of an energy-restricted diet, contributes to weight loss."

Despite this regulatory endorsement, clinical evidence on weight loss per se is mixed. EFSA approved the 3 g/day weight-loss claim in an energy-restricted diet, but a 2014 systematic review and meta-analysis by Onakpoya of 9 RCTs found no statistically significant weight loss versus placebo. Limited data suggest that, in the short term, glucomannan has the potential to reduce body weight, but not BMI, in adults.

In a systematic review and meta-analysis encompassing six RCTs, Mohammadpour et al. (2020) indicated that KGM may produce modest yet statistically significant effects on weight loss. However, their analysis exclusively focused on overweight and obese individuals, omitting studies involving subjects with hypertension, insulin resistance, glucose intolerance, and atherogenic dyslipidemia.

A more recent 2025 review reinforced the modest positive signal: KGM supplementation at ≥5 g/day for ≥12 weeks was frequently associated with reductions in BMI (mean: 1.49 kg/m²) and weight (mean: 3.18 kg). These data come from 10 RCTs reviewed between 2014 and 2024.

Regarding appetite specifically, evidence is somewhat stronger. The landmark meta-analysis by Onakpoya et al. (2014) published in Journal of the American College of Nutrition, pooling 8 randomized controlled trials (n=308), confirmed significant weight loss in the glucomannan group versus placebo, under caloric deficit conditions. An early double-blind trial found that glucomannan fiber (from konjac root) given in 1-g doses (two 500-mg capsules) with 8 oz water, 1 hour prior to each of three meals per day, resulted in a significant mean weight loss of 5.5 lbs over an eight-week period in 20 obese subjects.

Overall evidence strength for weight loss: Moderate for appetite suppression and satiety; contested and mixed for actual body weight reduction when dietary restriction is not controlled. The EFSA approval specifically restricts the claim to energy-restricted diets.

4.2 Blood Lipids (Cholesterol and Triglycerides)

The cholesterol-lowering effect of KGM is among the best-supported areas of clinical evidence. In the same early 8-week double-blind trial in 20 obese subjects, serum cholesterol and LDL cholesterol were significantly reduced by 21.7 and 15.0 mg/dL, respectively, in the glucomannan-treated group.

A meta-analysis (Hoang et al., 2017; 12 trials, adults) showed that on average 3 g/day of glucomannan reduces LDL cholesterol by approximately −0.35 mmol/L (−10%) and non-HDL cholesterol by approximately −0.32 mmol/L (−7%). This study concluded that approximately 3 g/day is sufficient for these significant reductions in LDL. A more recent systematic review (2024) of 14 RCTs showed that glucomannan supplementation induced a statistically significant decrease in total cholesterol (SMD −3.30, p<0.001) and LDL (SMD −2.99, p≈0.006).

In a randomized crossover metabolic trial in type 2 diabetic patients, KGM fiber-enriched biscuits (providing 0.7 g glucomannan per 100 kcal) significantly reduced the total:HDL cholesterol ratio by 10% (P=0.03) and systolic blood pressure by 6.9% (P=0.02) compared with placebo.

Overall evidence strength for lipid reduction: Moderate to strong. Multiple meta-analyses and RCTs consistently demonstrate reductions in LDL cholesterol and total cholesterol. EFSA has approved a maintenance claim for normal blood cholesterol concentrations at 4 g/day.

4.3 Blood Glucose and Type 2 Diabetes

Clinical evidence for glycemic benefits is positive but not fully consistent across all trials. In a crossover metabolic trial in type 2 diabetics using KGM fiber-enriched biscuits (0.7 g/412 kJ of glucomannan), KGM significantly reduced serum fructosamine by 5.7% (P=0.007) compared to placebo wheat bran.

Research has shown that KGM demonstrated significant efficacy in reducing glucose levels by 55.37% when administered at a dose of 1.5 g/kg in animal models and clinical settings. Additionally, konjac flour resulted in a 40.9% reduction in blood sugar levels under similar experimental conditions. In clinical trials involving type 2 diabetic patients, KGM supplementation has been associated with a reduction in fasting glucose levels by 23.2% compared to placebo.

However, results in the relevant literature have failed to reach a consensus; for example, konjac glucomannan significantly reduced fasting glucose in several studies, but Vuksan et al. showed that there was no significant difference. The heterogeneity of study designs, populations, doses, and durations limits firm conclusions.

EFSA has approved a health claim for KGM related to reduction of post-prandial glycaemic responses and maintenance of normal blood glucose concentrations, based on its review of the available evidence.

Overall evidence strength for glycemic control: Moderate for post-prandial glucose reduction and beneficial effects on fructosamine in type 2 diabetes, but results on fasting glucose are inconsistent across RCTs.

4.4 Bowel Function and Constipation

Glucomannan may work in the stomach and intestines by absorbing water to form a bulky fiber, which treats constipation. EFSA has approved a health claim for the maintenance of normal bowel function for KGM. A study cited in the EFSA dossier documented that konjac acts as a natural laxative by increasing stool bulk and improving colonic ecology in healthy adults.

Under KGM intervention, a decrease in colonic pH and an increase in the concentrations of acetate, propionate, and butyrate in stool were observed. These fermentation products of colonic metabolism are considered beneficial for intestinal health.

Overall evidence strength for bowel function: Moderate; this is one of the best-documented clinical effects, supported by mechanistic data and multiple trials, and is backed by an EFSA approved health claim.

4.5 Gut Microbiota (Prebiotic Effects)

Konjac gum and konjac glucomannan are unlikely to be absorbed intact and are significantly fermented by intestinal microbiota. This fermentation underpins prebiotic effects. Depolymerized KGM (DKGM), a degradation product of KGM, has been shown to improve the intestinal environment in numerous in vivo experiments. In in vitro tests, DKGM has shown a prebiotic effect that promotes the proliferation of beneficial lactic acid bacteria and intestinal microbiota.

The prebiotic properties of glucomannan foster a healthy gut microbiome, offering therapeutic possibilities for managing conditions such as irritable bowel syndrome (IBS) and other digestive disorders.

Overall evidence strength for prebiotic effects: Preliminary to moderate. Consistent mechanistic and in vitro data exist; human clinical evidence on specific microbiome composition outcomes is growing but not yet extensive.

4.6 Anti-inflammatory and Immune-Regulatory Effects

Emerging evidence highlights KGM's anti-inflammatory and immune-regulatory effects, with applications in managing inflammatory bowel disease, hyperthyroidism, and colorectal cancer (CRC). KGM has demonstrated efficacy in reducing pro-inflammatory cytokines such as TNF-α, IL-1β, IL-4, and IL-13, particularly in experimental models of colitis, atopic dermatitis, and skin inflammation. Additionally, KGM contributes to gut immune homeostasis by enhancing the growth of beneficial microbiota. Its application in wound healing further demonstrates its anti-inflammatory profile and biocompatibility.

A human study examined the tolerance and efficacy of low- and high-molecular-weight konjac glucomannan hydrolysates within healthy volunteers and patients suffering from IBD and associated gut conditions, including constipation, Crohn's disease, and ulcerative colitis. For general tolerance, 14 patients participated, while for the digestive disorder trial, there were 20.

Overall evidence strength for anti-inflammatory effects: Preliminary. The strongest data come from animal and cell culture models. Human clinical evidence specific to inflammatory bowel disease and related conditions is limited and requires further study.

4.7 Wound Healing and Skin Applications

KGM molecular chains contain a small amount of acetyl groups and a large number of hydroxyl groups, thereby exhibiting exceptional water retention and gel-forming properties that have been exploited in wound dressing research. In vitro study showed that KGM modified with gallic acid could stimulate macrophage polarization to the anti-inflammatory M2 phenotype and decrease reactive oxygen species levels. In vivo studies of skin wounds demonstrated that the KGM dressing significantly improved wound healing by accelerating wound closure, collagen deposition, and angiogenesis, and regulated M2 polarization, reducing intracellular ROS in the wound microenvironment.

Overall evidence strength for wound healing: Preliminary. Data are primarily from animal and in vitro models; clinical human trial evidence for wound healing applications is lacking.

5. Body Systems and Health Areas

• Gastrointestinal system: Bowel regularity, stool bulk, constipation relief, colonic pH modulation, microbiota modulation (prebiotic), and potential applications in IBD.
• Metabolic system: Blood glucose regulation, post-prandial glycemic response, fasting glucose in type 2 diabetes.
• Cardiovascular system: LDL cholesterol reduction, total cholesterol reduction, modest blood pressure reduction, triglyceride management.
• Endocrine system: Insulin sensitivity and insulin response modulation, proposed management of hyperthyroidism (emerging, limited human evidence).
• Immune system: Macrophage polarization, cytokine modulation, immune homeostasis through microbiota interaction.
• Integumentary system (skin): Traditional use for burns and skin disorders; modern research into KGM-based wound dressings.
• Body weight regulation: Satiety signaling, appetite suppression via gastric expansion and vagal nerve stimulation.

6. Dosage Forms and Dosages Reported in Studies

In one double-blind trial, glucomannan fiber (from konjac root) was given in 1-g doses (two 500-mg capsules) with 8 oz water, 1 hour prior to each of three meals per day (total: 3 g/day) over eight weeks.

In a study associated with the EFSA re-evaluation, a dosage of 3 g konjac glucomannan, divided into three times 1 g per person per day (corresponding to 33 mg/kg body weight per day based on a mean body weight of approximately 90 kg), for 12 weeks, was associated with gastrointestinal effects.

A 2026 placebo-controlled RCT tested the effects of glucomannan at 3 g/day over 12 weeks on body weight and composition, lipid profile, glucose metabolism, inflammation, adipokines, intestinal permeability, gut microbiota, and fecal metabolites in 40 adults.

A 2025 systematic review of 10 RCTs found that KGM supplementation at ≥5 g/day for ≥12 weeks was frequently associated with reductions in BMI and body weight.

A randomized controlled metabolic trial in type 2 diabetics used KJM fiber-enriched biscuits providing 0.7 g glucomannan per 412 kJ (100 kcal), during two 3-week treatment phases separated by a 2-week washout period.

Data suggest diarrhea, abdominal pain, and flatulence occur with dosages more than 5 g daily.

The EFSA health claims for cholesterol are associated with 4 g/day, and the weight-loss claim with 3 g/day in the context of an energy-restricted diet. The EFSA Panel agreed that uses of konjac as a food additive at levels up to 10 g/kg in food are acceptable, provided that the total intake from all sources stays below 3 g/day.

7. Safety Considerations and Drug Interactions

General Gastrointestinal Effects

Minor adverse effects are normally gastrointestinal-related and include diarrhea, flatulence, abdominal discomfort, and bloating. After a daily dosage of 3,000 mg in adults for 12 weeks, several individuals experienced abdominal discomfort including diarrhoea or constipation.

Esophageal and Gastrointestinal Obstruction

This is the most serious documented safety risk. Severe esophageal and GI obstruction have been reported with glucomannan tablets. Several cases of severe esophageal obstruction due to glucomannan diet tablets have been reported. Seven cases were noted during 1984 and 1985 by the Australian Adverse Drug Reactions Advisory Committee. Four of these obstructions occurred in the proximal one-third of the esophagus. One patient developed mediastinitis due to perforation of the esophagus. Thus, patients with conditions of the esophagus or who experience difficulty swallowing in general may be at increased risk of esophageal obstruction associated with glucomannan.

A published case report describes a 37-year-old female who developed delayed esophageal obstruction after ingesting an over-the-counter diet aid containing glucomannan. The patient cleared the obstruction through forceful emesis, just prior to upper gastrointestinal endoscopy. She was noted to have an esophageal web. This case illustrates the potential dangers of glucomannan and other hygroscopic medications in patients with a history of upper gastrointestinal pathology.

Given the risk of esophageal and gastric obstruction, use is not recommended in patients with structural abnormalities of the esophagus or gut.

Dosage Form Risks

Tablet formulations carry the highest esophageal obstruction risk. Powder mixed in water before consumption is considered the safest form. Capsules expand more slowly than tablets but still require adequate water co-administration. In some jurisdictions, konjac jelly candies have been banned due to choking hazards, particularly for children and elderly individuals.

Drug Interactions

Reported negative effects include flatulence, abdominal pain, gastrointestinal obstruction, and possible modification of the bioavailability of other medications. The hypoglycemic effects are potentially dangerous to patients with diabetes taking glucose-lowering medications. Glucomannan has been linked in case reports to cholestatic hepatitis and occupational asthma. Key unknowns remain: long-term safety beyond one year, pregnancy and lactation data, and high-quality studies on clinically important interactions with warfarin and other narrow therapeutic index drugs.

Genotoxicity and General Toxicological Findings

Konjac gum and konjac glucomannan would be of no concern with respect to genotoxicity; no relevant adverse effects were seen in rats and dogs in 90-day feeding studies, and the no-observed-effect level (NOEL) in rats was 1,250 mg konjac glucomannan/kg body weight per day. The EFSA Panel concluded that there was no need for a numerical acceptable daily intake (ADI) and that there was no safety concern for the general population at the refined exposure assessment for the reported uses of konjac gum and konjac glucomannan as food additives under the current conditions of use of 10 g/kg.

Pregnancy and Lactation

Information regarding use during pregnancy and lactation is lacking. Until more information is obtained, use is not recommended in pregnant or breast-feeding women.

References

• Frontiers in Plant Science / PMC: Amorphophallus konjac: traditional uses, bioactive potential, and emerging health applications (2025)
• ScienceDirect: Traditional uses and potential health benefits of Amorphophallus konjac K. Koch ex N.E.Br. (2010)
• ScienceDirect Topics: Amorphophallus konjac — Overview
• ScienceDirect: Konjac Glucomannan: A functional food additive for preventing metabolic syndrome (2024)
• PMC / EFSA Journal: Re-evaluation of konjac gum (E 425 i) and konjac glucomannan (E 425 ii) as food additives (2017)
• EFSA: Scientific Opinion on health claims related to konjac mannan (glucomannan) (2010)
• EFSA: Re-evaluation of konjac gum (E 425 i) and konjac glucomannan (E 425 ii) as food additives (2017)
• PubMed: Konjac-mannan (glucomannan) improves glycemia and other associated risk factors for coronary heart disease in type 2 diabetes. A randomized controlled metabolic trial
• PubMed: The effect of glucomannan on body weight in overweight or obese children and adults: a systematic review of randomized controlled trials (2015)
• ScienceDirect: Effects of glucomannan supplementation on weight loss in overweight and obese adults: A systematic review and meta-analysis of randomized controlled trials (2020)
• PMC: Effects of Glucomannan Supplementation on Type II Diabetes Mellitus in Humans: A Meta-Analysis
• Springer / Discover Food: Konjac glucomannan as an emerging nutritional strategy for obesity control via gut microbiota and metabolic regulation (2025)
• PubMed: Esophageal obstruction from a hygroscopic pharmacobezoar containing glucomannan
• PMC: Depolymerized konjac glucomannan: preparation and application in health care
• PMC: Review of Konjac Glucomannan Structure, Properties, Gelation Mechanism, and Application in Medical Biology
• PMC: Extraction, structure, activity and application of konjac glucomannan
• British Journal of Nutrition: Effects of gelled konjac glucomannan fibre on appetite and energy intake in healthy individuals: a randomised cross-over trial
• Drugs.com Natural Product: Glucomannan uses, benefits and dosage
• medRxiv: Konjac Glucomannan Improves Body Composition and Reduced Blood Cholesterol, Inflammation, and Cardiovascular Risk in Adults with Excess Weight (2026, preprint)
• PubMed: Amorphophallus konjac: traditional uses, bioactive potential, and emerging health applications (2025)