Fiber May Not Be Way to Ward Off Cancer
We’ve been resisting fried chicken and doughnuts. We’ve been stocking up our kitchens with whole grain breads, bran flakes and fruits and vegetables. And now, depressing news--especially for anyone with a family history of cancers of the colon or rectum. In two studies reported last week, scientists found that high-fiber diets--long trumpeted as ways to ward off these cancers--apparently don’t do so.
The two large, controlled studies, published in the New England Journal of Medicine, tested such diets in people who had previously had at least one colon polyp removed. The people in the reports altered their diets--in one study, lowering fat and upping intake of fruits, vegetables and other sources of dietary fiber, and in the other, supplementing their diet with wheat bran fiber.
But over the course of several years, both groups developed additional colorectal adenomas--the type of polyp that can sometimes lead to cancer--at similar rates to folks who didn’t alter their diets.
These findings, which came as a surprise and a disappointment to many researchers, are discouraging news for people who hope that watching their diet can help them live longer, healthier lives. Colorectal cancer, after all, is not a rare disease: The American Cancer Society predicts that more than 130,000 Americans will be diagnosed with it this year and that more than 56,000 people will die from it. It would be nice to think there are measures we can take to avoid the scourge.
There are, experts stress.
The best protective measure--as it was before the two studies--is regular screening, starting at about age 50 (possibly earlier for people with family histories of the cancer). In that procedure, doctors using flexible probes examine all or part of the colon and remove any polyps they find.
“This is the cornerstone of protection from the disease--you eliminate 80% to 90% of the risk by removing polyps,” says James R. Marshall, professor of public health at the Arizona Cancer Center at the University of Arizona in Tucson, and a coauthor on both of the studies.
There’s also evidence that other measures we can take--exercising more, staying or becoming lean, eating less red meat, getting adequate folic acid and quitting smoking--may all reduce the risk of colorectal cancer (though these measures, too, need to be tested further, experts say).
“All these things together can probably prevent at least 70% of colon cancers,” says Dr. Walter Willet, professor of epidemiology and nutrition at Harvard School of Public Health in Cambridge, Mass.
Calcium supplements may also modestly protect against polyps. In a study reported last year, patients with a history of polyps had a 15% lower risk of a subsequent polyp after taking calcium carbonate supplements for four years. Selenium supplements may protect against colon cancer too.
But fiber? Keep eating a fiber-rich diet, urge scientists. There are many good reasons to do so.
“The message should be that fiber is still a very healthful part of the diet because it really reduces the risk for a number of chronic diseases, including coronary heart disease, hypertension and diabetes,” says Dr. David Alberts, director of cancer prevention at the Arizona Cancer Center and lead author on the wheat fiber study.
Hemorrhoids, vein inflammation, and inflammations and infections of the colon--can also be avoided by eating enough fiber.
Diets high in saturated fats and trans fatty acids, meanwhile, have been linked to maladies such as heart disease. And fruits and vegetables are packed with disease-fighting antioxidants.
What’s more--though opinions are divided on this--some scientists don’t think these two studies are the final word on the fiber-colon cancer link.
Willet is one who thinks the answer is in.
“The results aren’t really surprising, given what we’ve observed in other studies over the last several years,” he says. “Ten years ago, it did seem that low fat and fiber might be the most productive way to prevent colon cancer. But that has not been supported in studies since that time.”
Others, though, point to a wealth of evidence--from epidemiological and animal studies--that link a low fat, high-fiber diet rich in fruits and vegetables to reduced colon cancer risk. The American Cancer Society cautions against throwing in the towel on such diets.
What’s more, the patients examined in the two new studies were, on average, in their 60s and so didn’t have youthful, pristine colons. All had already developed polyps, says Dr. Arthur Schatzkin, chief of the Nutritional Epidemiology Branch at the National Cancer Institute in Bethesda, Md., and lead author of one of the studies. Perhaps the intervention came too late, after too many years of a diet of cheeseburgers and fries.
“The development of cancer is a long process--it may be that diet works earlier on, before a person develops their first polyp,” he says.
New drugs--including one just approved by the U.S. Food and Drug Administration for use in people who have a familial kind of colon cancer--are being developed to help treat polyps.
And scientists are still hashing out the best way to examine people’s colons. Such screenings can be done via a sigmoidoscopy, which takes about 15 minutes and examines the lower half of the colon, or a more involved procedure called a colonoscopy, in which the entire colon is viewed. In the study led by Alberts, many of the polyps were found further up in the colon and wouldn’t have been revealed by a sigmoidoscopy. This, write the authors, suggests that colonoscopy is the preferred exam, especially if people have had polyps in this area before.
Some people, of course, may be squeamish about the prospect of either procedure--but they shouldn’t be, Alberts says. Colon cancer runs in his family: So far he’s had 14 colonoscopies and counting.
“No, I won’t say I look forward to them--but frankly, they’re not that bad.”
