Glucomannan is a fermentable dietary fiber that's in konjac, and it turns out that human salivary and enzymes in our mouth cannot split linkages of glucomannan, so this fiber passes relatively unchanged into the colon until the bacteria in the colons ferment it afterward. That’s why konjac is said to be beneficial for people who are looking to lose or maintain a healthy weight. Additionally, konjac absorbs water in the gastrointestinal tract to form a fiber, which in turn controls cholesterol levels.