Will the real relation between dietary fiber and colorectal cancer please stand up? Depending on the study design and type of fiber investigated, reports find that fiber protects you from colorectal cancer, does nothing, or even bumps up your risk. The latest big study, published in the December 14, 2005, Journal of the American Medical Association, pooled the results from 13 prospective studies, which together tracked some 725,000 people for up to 20 years. Although they could not control for confounding dietary factors or solubility of fiber, the authors found that those eating the least fiber (less than 10 grams a day) were at increased risk of colorectal cancer. But high intake of fiber did nothing to reduce risk. The results also suggested that fiber from cereals and whole grains, but not from fruits and vegetables, confers a somewhat lower risk of rectal cancer.
This article was originally published with the title "Fiber Irregularities" in Scientific American 294, 2, 29 (February 2006)