Glucomannan is a polysaccharide derived from the tuber of the konjac plant, Amorphophallus konjac. It is used as a thickening agent in foods and is marketed in the United States as a dietary supplement. Glucomannan is considered a soluble dietary fiber that is indigestible by human intestinal enzymes. It can be degraded by intestinal bacteria into short chain fatty acids, such as propionic and butyric acids 1. Glucomannan is likely safe when used orally as food 2.