The everyday diet should deliver to the organism the appropriate quantity of nutritious elements. Beside these elements the important feeding function fulfils the alimentary cellulose which is not digested and not absorbed from the alimentary tube. This compound exerts positive influence on some metabolic and physiological processes setting in the organism. A rich diet in dietary fiber plays an important role in the prevention and treatment of the diseases of an alimentary and blood system, diabetes, the tumors of thick intestine, kidney stone, hemorrhoids and the metabolism disturbances. In this article the notion of dietary fiber, its principal sources with the division on solvable dietary fiber and insoluble and its influence on a man’s health is presented.