From The February 2001 Issue of Nutrition Science News

Colon Cancer Prevented, Promoted by Diet

Adding to the confusion of current research regarding diet and colon cancer, a pan-European study shows that calcium supplementation may prevent colorectal cancer recurrence while soluble fiber supplementation may increase it. The European Cancer Prevention Organization (ECP) intervention study, directed by Claire Bonithon-Kopp, M.D., of the Medical School of Dijon, France, involved 10 countries ranging from Ireland to Israel. The 552 participants had previous colorectal cancer (65 percent women, average age 59) and were randomly divided into three groups, then supplemented daily for three years. The first group received 2 g calcium, the second group 3.5 g soluble fiber as ispaghula (Plantago ispaghula) husk, and the third group a placebo.

During the three years, colorectial adenomas developed in 16 percent of the calcium group, 20 percent of the placebo group, and 29 percent of the fiber group. The calcium group reduced their risk of recurrent colorectial adenoma by 33 percent. Soluble fiber, on the other hand, was associated with an increased risk of adenoma recurrence. The soluble fiber group as a whole had a 50 percent higher chance of recurrence. However, the response to soluble fiber supplementation depended on subjects' baseline dietary calcium. If below median, soluble fiber supplementation did not increase their risk of a recurrence, but if it was above median their risk increased by 280 percent. The researchers did not test the combination of calcium and fiber supplementation together.

These results were unexpected and confusing. Why should calcium supplementation by itself reduce risk; but the combination of adequate calcium and soluble fiber increase risk? And why should ispaghula husk, a powerful colon tumor protector in animals, increase the risk in humans? One explanation might be that the soluble fiber and calcium connected to each other so strongly that they were unable to bind to carcinogenic bile acids, leaving these acids free to cause new adenomas. In conjunction with recent studies showing a lack of protection by insoluble fiber (see "Low Fat, High Fiber Doesn't Cut Colon Cancer Risk"), this new research runs contrary to the hypothesis—and hope—that fiber prevents the initial stages of colon cancer development, although it does not rule out the possibility that it helps protect against later stages.

—The Lancet
2000 Oct 14;356:1300-6.