Best Naturals Konjac Root Glucomannan Powder 1 lb. Glucomannan is a soluble bulk-forming fiber derived from Konjac Root (Amorphophallus konjac). Glucomannan is a water-soluble polysaccharide with hygroscopic properties and is considered a dietary fiber. Glucomannan is an excellent addition to a sensible weight loss program (Natural source of fiber).*