Fiber, steroids, and cancer.

Fiber is a generic term for dietary components which are not metabolized by intestinal secretions. Fiber encompasses a variety of substances of unique structure having specific physical characteristics and physiological function. There are a number of epidemiological and case-control studies on diet and colon cancer, many of which suggest that dietary fiber or fiber-rich foods may exert a protective action, but the view is not unanimous. One study finds a negative correlation between cancer mortality and pentose-rich dietary fibers. Animal studies have been carried out using rats of different strain, semipurified or commercial diets, and various carcinogens administered in a variety of ways. Again, there is no unanimity. The results depend upon the type of fiber and the route of carcinogen administration. Some type of fiber bind bile acids and salts, and this property has been investigated as a means of explaining the protective action of fiber. Several recent studies in human subjects suggest that susceptibility to colon cancer is related inversely to the concentration of fecal bile acids rather than to the absolute quantity of fecal bile acids or their structure. Future studies require better standardization of protocols so that intradietary effects can be assessed.