Study: Fiber Fails To Prevent Colon Cancer
B O S T O N, October 13, 2000 -- The belief that a diet high in fiber can prevent colon cancer continues its downward spiral, with a new report further discrediting the once highly regarded theory.
A team of European researchers reporting Thursday in the British journal Lancet found fiber as an additive to food did not seem to prevent the formation of potentially cancerous polyps in the colon.
But doctors say your morning bowl of bran shouldn’t be dumped entirely: fiber, which is found in fruits, veggies, nuts and grains, probably still can lower cholesterol, improve bowel regularity and help diabetics control their blood sugar.
The Lancet study comes on the heels of two high-profile reports published in the New England Journal of Medicine in April that found no link between colon cancer prevention and a high-fiber diet, consumed either as a supplement or as part of a whole food. The association has been nearly dogma among health-care professionals for decades.
In fact, the Food and Drug Administration in 1993 approved claims that low-fat diets rich in fiber-containing grain products, fruits and vegetables “may reduce risk of certain cancers,” allowing food manufacturers to advertise those properties on the sides of cereal boxes.
But this week, the agency announced it would not permit any dietary supplement manufacturer to make the more direct claim that fiber can reduce the risk of colon cancer, in light of more current evidence.
History of a Hypothesis So how did the theory of fiber and cancer risk ever come to pass? The idea dates to an observation made by Dr. Denis Burkitt, a British missionary doctor who in the early 1970s compared colon cancer rates between America and Africa. He attributed the high cancer incidence in affluent Western countries to diets high in animal fats, and the low cancer rates in poorer countries such as Africa to the diets high in plant-based fiber.
Initially, research in animals and observations of large populations seemed to bear out his theory.
Doctors posited fiber prevented colon cancer by binding to cancer-causing substances or by acting as a laxative. Fiber, they argue, absorbs water, lubricates the feces and decreases the amount of time the potentially contaminated excrement remains in the colon. Both actions would lower the interaction of any carcinogens in the stool with the cells lining the colon.
More Contradictory Results
But now, doctors seem to have better evidence contradicting the early results.
In this most recent study, researchers of the 21-center European Cancer Prevention study randomly assigned 655 patients with a history of developing polyps to take calcium, fiber supplements or a dummy pill. After three years, the patients had a colonoscopy, a test that inspects the colon and removes precancerous polyps.
The doctors found that 29 percent of those taking 3.5 grams of soluble fiber daily, developed at least one polyp, compared to only 20 percent of those taking a placebo pill. Previous studies had mainly tested the effects of insoluble fiber, found in wheat and rice, rather than soluble fiber, found in oats and barley.
“Our findings did not accord with the hypothesis of a preventive effect of fiber on the risk of colon cancer,” wrote the researchers, led by Dr. Claire Bonithon-Kopp of Dijon, France.
Finale on Fiber? Some scientists say the findings of these new studies should not be considered the final word.
Ritva Butrum, vice president of research for the American Institute for Cancer Research, believes a high-fiber, low-fat diet may need to be maintained as a “lifelong commitment, not a stop-gap measure.”
Perhaps the three-year intervention was not long enough to make a difference in such a slow-progressing disease, she says. Sprinkling fiber supplements on top of a high-fat diet may fail to work as effectively as changing one’s diet overall, says Cheryl Rock, a cancer prevention specialist at the University of California in San Diego. Supplements may contain different ingredients than a diet of fruits and vegetables which contains fiber and other possible cancer-fighting ingredients, she adds.
One of the NEJM studies did look a patients assigned to take a high-fiber, low-fat diet and still found it did not reduce their risk of developing colon polyps. But critics like Rock say that those study participants did not rigorously adhere to the diet.
Firm Evidence But several experts are convinced these results provide firm evidence that fiber should be abandoned as a colon cancer cure-all.
“I don’t think there’s very compelling data for fiber anymore,” says Dr. Charlie Fuchs, a medical oncologist at the Dana-Farber Cancer Institute in Boston, whose findings last year from the Nurses Health Study, which followed 90,000 women for 16 years, also negated the high-fiber diet/reduced-cancer link. “Let’s spend our money trying to find a hard-earned answers rather than beating this one to a pulp.”
Dr. Bernard Levin, vice president of cancer prevention at the University of Texas’s M.D. Anderson Cancer Center in Houston wrote in an accompanying editorial that these findings should spur research into other preventives, such as non-steroidal anti-inflammatory drugs like aspirin.
Colon cancer is the second leading cause of cancer death in the United States. Around 130,000 Americans are diagnosed with colon cancer annually. Those rates have been dropping, according to the American Cancer Society, largely because of better treatments and improved early detection.