Dietary fibers: their definition and nutritional properties

Fiber is a variable material with respect to its nutritional qualities depending upon its composition and physical properties. Biological properties possessed by one type of fiber might not be shared by another type. Separate methods are required to describe quantity, composition, and quality of fiber in foods. Fibers can be generally classified into three groups: vegetable fibers, which are highly fermentable with low indigestible residue; brans, which are less fermentable; and chemically purified fibers such as wood cellulose, which are relatively unfermentable. A class of soluble substances including pectins and gums may not be true fibers, but are considered part of the dietary fiber complex because of the similar effects they can elicit in the diet. A major need is the replacement of the crude fiber method, the present official method, which is seriously defective. Since crude fiber values are erratic and poorly related to the true fiber value of food, a second major need is the reanalysis of all foodstuffs by appropriate methods and the replacement of standard tables of food composition. Accomplishment of these purposes will require more support and promotion than is presently being received.