Konjac glucomannan

Konjac glucomannan is a high-molecular-weight polysaccharide that can absorb up to 50 times its own weight in water, forming a highly viscous gel in the stomach. This rheological behaviour is central to its satiating effect (Parry, 2009). Once ingested, the resulting increase in gastric volume promotes mechanical distension and activates mechanoreceptors in the stomach wall, helping trigger an earlier feeling of fullness (Salleh et al., 2019). The increased viscosity of the chyme also slows gastric emptying, helping extend postprandial satiety (Shang et al., 2020).

From a clinical perspective, Birketvedt et al. (2005) reported significant weight loss with glucomannan supplementation in a controlled trial involving 176 overweight subjects following a calorie-restricted diet. Earlier, in a randomized, double-blind trial in obese patients, Walsh et al. (1984) found that 3 g/day for 8 weeks produced greater weight loss than placebo.

In a controlled crossover trial, Shang et al. (2020) incorporated 4 g of glucomannan into a test meal and showed that, by increasing the viscosity of gastric contents, glucomannan significantly delayed gastric emptying. This higher viscosity was associated with increased levels of satiety-related hormones (GLP-1, PYY, CCK) and reduced ghrelin levels, leading to a measurable decrease in hunger and food intake at the following meal.

Beyond its bulking effect, the viscous gel formed by konjac glucomannan may act as a diffusion barrier in the intestine, limiting the access of digestive enzymes to their substrates and slowing the absorption of glucose and lipids (Parry, 2009). This mechanism may help attenuate postprandial glucose spikes and support improvements in selected lipid markers.

With regard to lipid metabolism, a 2008 meta-analysis of 14 randomized controlled trials reported that konjac glucomannan supplementation was associated with significant reductions in total cholesterol (≈ −19 mg/dL) and LDL-cholesterol (≈ −16 mg/dL) (Sood et al., 2008). A more recent analysis including 12 trials confirmed a mean LDL reduction of approximately 0.35 mmol/L at doses close to 3 g/day (Ho et al., 2017).

In terms of glycaemic regulation, a meta-analysis of 12 randomized controlled trials (≈ 840 participants) showed that supplementation with approximately 3 g/day of glucomannan for 4 to 8 weeks significantly reduced fasting blood glucose and fasting insulin levels (Ashtary-Larky et al., 2022). Complementary evidence from a meta-analysis conducted in 440 patients with type 2 diabetes confirmed significant reductions in fasting blood glucose, postprandial blood glucose and glycated haemoglobin (HbA1c) after 4 to 12 weeks at 3–5 g/day (Zhang et al., 2023).

Glucomannan is a fermentable soluble fibre that can serve as a substrate for the gut microbiota and support the growth of beneficial bacteria such as bifidobacteria and lactobacilli. Its fermentation leads to the production of short-chain fatty acids (SCFAs), including butyrate, which helps maintain intestinal barrier integrity and regulate local immune responses. SCFA production also lowers intestinal pH, contributing to the maintenance of a balanced gut microbiota (Changchien et al., 2020).

In healthy adults, these mechanisms have been supported by a controlled study showing that konjac glucomannan supplementation (4.5 g/day) increased bifidobacteria and lactobacilli, as well as SCFA levels, while reducing faecal pH (Chen et al., 2006).

A randomized, double-blind trial also reported an increase in these beneficial bacteria, together with reductions in β-glucuronidase*, secondary bile acids and faecal water toxicity (Wu et al., 2011). These findings suggest that glucomannan may help promote a healthier intestinal environment and has potential as a prebiotic ingredient.

*Bacterial enzyme involved in the reactivation of potentially harmful compounds.

However, when they are used for nutritional purposes, as in food supplements, konjac gum and konjac glucomannan are no longer additives and the “Specific Maximum Level” does not apply. They can therefore be incorporated into capsules at much higher doses.

Konjac glucomannan is listed in the 4th edition of the Food Chemical Codex (1996).

The US Food and Drug Administration (FDA) has classified konjac flour as “generally recognized as safe” (GRAS) (FDA, 1997).

The 40 mesh grade of konjac glucomannan is particularly well suited to capsules thanks to its high bulk density, which helps optimise dosage formats.

Functional properties

• High fibre content (TDF/DM ≥ 95%) : enables 1 g of glucomannan to be delivered in 2 size 0 capsules
• High bulk density : optimised filling and compact formats
• Gradual hydration after ingestion

Typical applications

• Slimming food supplements
• Satiety / weight management formulas
• Products for digestive comfort

The low-viscosity (LV) grade is designed for liquid applications requiring high fibre fortification without compromising flowability.

Functional properties

• Low viscosity, even at high inclusion levels : fibre enrichment without excessive thickening
• Non-gelling behaviour : maintains the flowability of liquid matrices
• Rapid hydration : easy incorporation and uniform dispersion
• Suspension stabilisation : compatible with complex liquid matrices (proteins, particulates)

Typical applications

• Fibre-enriched functional beverages
• Nutritional RTD products

The fine particle size of 120 mesh glucomannan enables rapid and uniform dispersion.

Functional properties

• Rapid cold hydration → efficient dispersion and reduced lump formation
• Fine particle size → improved solubilisation and blend homogeneity
• Controlled viscosity development → stability and texture control

Glucomannan is a fibre in accordance with Regulation (EU) No. 1169/2011 on the provision of food information to consumers (FIC Regulation).

Glucomannan-based food products may claim to be:

• “source of fibre” if they contain at least 3 g of fibre per 100 g or 1.5 g of fibre per 100 kcal.
• “high in fibre” if they contain at least 6 g of fibre per 100 g or at least 3 g per 100 kcal.

According to Commission Regulation (EU) No. 432/2012, two health claims may be made on foods and food supplements containing konjac glucomannan.