Over the past two decades, reports have linked a high daily consumption of dietary fiber to reduced risk of cancers of the colon, rectum, and other gastrointestinal sites. However, the Boston team notes that other studies of dietary fiber produced conflicting results. Many of these studies did not permit a clear distinction to be made between the effects of fiber and those of other constituents of plant foods. In one of the largest and longest prospective studies of its kind to date, the investigators followed the 16-year dietary and medical histories of nearly 89,000 women as part of the ongoing Nurses' Health Study.
"We found no association between the intake of dietary fiber and the risk of colorectal cancer," the authors report.  They found that the 20% of study subjects consuming the highest amounts of dietary fiber per day had a nonsignificant 5% lower incidence of colorectal cancer, compared with women consuming the lowest amounts of dietary fiber.
The researchers report that according to their data, a high consumption of vegetable-derived fiber was actually associated with a significant increase (35%) in the risk of colon cancer. Previous studies supporting the anti-cancer benefits of fiber were largely based on retrospective research.
When you ask people to recall (dietary patterns in) the remote past, there's always the potential problem that you can exaggerate the factor you're looking at -- in this case fiber. So, those studies are important, but they're hardly definitive. In contrast, the Nurses' Health Study remains one of the largest and most-respected prospective studies ever undertaken, where researchers study medical histories and record events as the participants experience them.
The New England Journal of Medicine January 21,1999;340:169-176, 223-224
COMMENT: Interesting to note that fiber may actually INCREASE colon cancer. I am quite sure that it is related to the fact that when one eats fiber in this country one is likely eating it in the form of bread. Anyone reading this newsletter should be aware that grain carbohydrates INCREASE the risk of cancer by increasing insulin levels. I suspect that is the relationship that is being observed in this research. If one wants to decrease colon cancer, calcium and folic acid appear to be particularly useful.