Definition of dietary fiber and hypotheses that it is a protective factor in certain diseases.

Crude fiber (CF) is the residue of plant food left after extraction by dilute acid followed by dilute alkali. Dietary fiber (DF), a new term, is the residue of plant food resistant to hydrolysis by human alimentary enzymes. DF is composed of cellulose, hemicellulose, and lignin; these constituents are not reported in food tables. For instance, whole wheatmeal has DF about 11%, CF about 2%. It is suggested that a new term, dietary fiber complex (DFC), should include all substances of DF plus all chemical compounds naturally associated with, and concentrated around, these structural polymers. CF supplies from starchy staples, wheat and potato, in England and Wales were probably stationary from 1770 to 1860, fell greatly from 1860 to 1910, rose during food controls in 1942 to 1953, and declined slightly from 1954 to 1970. It is postulated that fiber is a protective factor against certain colonic disorders, such as diverticular disease, and certain metabolic diseases, such as ischemic heart disease, diabetes mellitus, and obesity. These three diseases had changing trends of mortality rates in England during the food control years. Westernization of African diets is accompanied by a large fall in CF from starchy foods and vegetables and an increased prevalence of the same three diseases.