Glucomannan is a water-soluble polysaccharide that is considered a dietary fiber.

Glucomannan is a food additive used as an emulsifier and thikener. Products containing glucomanan, marketed under a variety of brand names, are also sold as nutritional supplements for constipation, obesity, high cholesterol, acne vulgaris and type 2 diabetes. Though there is some clinical support for potential health benefits.

Glucomannan comprises 40% by dry weight of the roots or corm of the konjac plant. It is also a hemicellulose that is present in large amounts in the wood of conifers and in smaller amounts in the wood of dicotyledons.