The Effect of Dietary Fiber on Fecal Weight and Composition

Abstract

Present-day interest in fiber stems from the middle of the nineteenth century when the preoccupation of the Victorians with their bowel habits led many physicians to declaim the virtues of bran. John Burne,1 writing in 1840 in A Treatise on the Causes and Consequences of Habitual Constipation, recommends that “coarse brown and bran bread is very efficacious, the bran acting as a salutory stimulus to the peristaltic action of the intestines.” There was little need to convince Burne and his generation that bran stimulated colonic movement and increased fecal output. Nevertheless, each generation of medical scientists seems to have to rediscover this fact for itself, and medical and nutritional literature in the 1970s contained many papers in which little else but the laxative properties of bran were reported. By 1909, Sir Arthur Hertz (later Sir Arthur Hurst)2 was writing, “One of the most valuable foods for constipation in whole-meal bread ... white bread, which is made of the endosperm alone and those varieties of brown bread, such as Hovis, which are made from the endosperm and germ, contain only about one-fifth of the cellulose present in whole-meal bread. It is clear, therefore, that the substitution of whole-meal bread for white bread is a very important part of the dietetic treatment of constipation.” Thus, 75 years ago fiber was being singled out as the principal component of bran responsible for its colonic effects. In 1936, Dimock,3 in his M.D. thesis for the University of Cambridge entitled “Treatment of Habitual Constipation by the Bran Method,” was able to review over 50 papers reporting clinical, biochemical, radiological, and physiological studies of the use of fiber in constipation. He discussed various current ideas about the way bran produces its laxative effect, such as the presence of undigestible fiber, its content of vitamin B, phytin, hemicellulose, inorganic salts, and the production of volatile fatty acids from decomposition of cellulose and hemicellulose. As a result of his own observations, he concluded, “My view is that bran exerts a mechanical laxative action due to its fibre content. The fibre mixes intimately with the food residues in the colon, even when bran is taken only once a day. I believe that by so doing, it not only retains moisture itself but enables the other residues in the colon to resist dehydration.” The 1930s were a time of vigorous investigation of the laxative properties of dietary fiber. Purified forms of fiber such as ispaghula, various celluloses, agar, karaya, sterculia, and psyllium