Recent advances in dietary fiber and colorectal diseases.

Dietary fiber has emerged in the past decade as a factor in nutrition that appears to have complex physiological and clinical implications. A great deal of research has focused on its effect on colorectal diseases. Some human epidemiological studies on colon cancer point to a possible preventive role of dietary fiber, but the results are confounded by the difference in the intake of many other food substances such as fat and the overall differences in the dietary pattern of the populations investigated. Animal studies using chemical carcinogens, such as 1,2-dimethylhydrazine, have lent support to a protective role of certain components of fiber, such as purified cellulose. Other fiber polymers, such as pectin, have not shown any protective effect. Perhaps the strongest evidence for a protective role of fiber in the colon comes from studies relating low dietary fiber intake to the higher incidence of diverticular disease of the colon; addition of dietary fiber to the diet of patients with symptomatic diverticular disease seems to relieve pain effectively. Recently, some preliminary studies have shown the possible correlation of low dietary fiber intake with a greater incidence of ulcerative colitis and Crohn's disease, but these studies are too limited in number and scope to allow any conclusion to be reached at this time.