Cereals, cereal fibre and colorectal cancer risk: a review of the epidemiological literature.

Burkitt and Walker first promoted the idea that colorectal cancer could be prevented by dietary fibre. Early studies of this hypothesis were hampered by problems with the definition of dietary fibre, and the lack of good analytical methods to assess its intake. Dietary fibre is a complex carbohydrate of plant origin that escapes small-bowel digestion and so reaches the colon. It was assumed that the major plant polysaccharide, starch, is completely digested in the small bowel, and that dietary fibre consists of nonstarch polysaccharide. However, there is some evidence that nonstarch polysaccharide accounts for only about 25% of the true intake of dietary fibre. Therefore it is better at present to use fibre-rich foods as a measure rather than the inaccurate assays of dietary fibre found in epidemiological studies. A re-examination of the epidemiological literature has shown that although the strength of the protection given by dietary fibre may be disputed, there is no doubt about the protection afforded by cereal fibre.