Fiber Doesn’t Deter Cancer, Study Finds

Eating lots of fiber does not appear to protect people from colon cancer, according to an ongoing study of 88,000 women that contradicts federal dietary guidelines and will surprise many a grudging bran consumer in mid-bite.

In the 16-year study by Harvard researchers, women who consumed a substantial 25 grams of fiber daily had the same risk of colon or rectal cancer as did women consuming a meager 10 grams. The U.S. average daily intake of fiber is 13 grams, and public health authorities recommend 20 to 35.

The new results, made public today in the New England Journal of Medicine, counter the popular nutrition wisdom promoted by health agencies, cereal companies and health gurus. The study is the largest and longest-running of its kind to address the question.

“Our findings do not support the notion that fiber is protective against colon cancer,” said the lead author, Dr. Charles Fuchs of the Dana-Farber Cancer Center in Boston. He said he used to strongly recommend high-fiber diets to patients as a means of preventing colon cancer, but stopped doing so after seeing the new data.

However, Fuchs and other medical researchers say that people eating a fiber-rich diet for other reasons should not give it up. Fiber, or indigestible plant material, can help regulate digestive function and substantially reduce the risk of heart disease and symptoms of diabetes, among other benefits, studies have shown.

Still, this new finding is expected to send a shock wave through medical and nutrition circles. And it appears to deal a symbolic blow to the whole-food fad, the movement to avoid refined or excessively processed foodstuffs that is partly tied to the 30-year-old theory that fiber could prevent colon cancer.

But if this apparent fiber flip-flop is maddening to consumers, experts said it should not be taken as grim news about colon and rectal cancer, which health authorities tally as “colorectal” cancer.

Disease Much Less Deadly Now

Though the disease remains the third leading malignancy in the United States--with about 129,400 people afflicted this year--it is less common and less deadly today than a decade ago, thanks to early screening, removal of precancerous lesions and other factors.

Researchers have gathered evidence that physical exercise, high intakes of the vitamin folic acid and the mineral calcium, regular low-dose aspirin consumption, and hormone replacement therapy in post-menopausal women reduce colon cancer risks.

While the new data found no benefit of fiber in colon cancer prevention, it “doesn’t end the story,” said Dr. Arthur Schatzkin, a medical epidemiologist at the National Cancer Institute, who has done studies on the question.

One limitation of the study, he said, was its reliance on the subjects’ responses to periodic dietary questionnaires, which can be misleading. “There is a lot of error in those dietary assessments,” he said, “and that error can obscure modest effects that are real.”

Shoppers interviewed Wednesday expressed suspicion of this latest nutrition reversal. At the Follow Your Heart natural foods store and restaurant in Canoga Park, Pierce Community College student Amy Copeland said: “Five years from now, they’ll come out with another study saying ‘we were wrong, it really does help fight cancer.’ ”

Not that consumers crave a reminder, but the new study shows once again that the role of diet in causing or preventing cancer is complex. At the very least, Fuchs said, the Harvard research undermines the widely held view that fiber simply scrubs cancer-causing chemicals out of the digestive tract. “The common-sense picture of things is not always the right one,” Fuchs said.

The fiber hypothesis got started three decades ago when British physician Denis Burkitt noted that some African populations had much less colon cancer than did Westerners. He speculated that the reason was diet: Africans ate foods high in fiber, whereas Westerners relied heavily on refined white flour and the like.

Researchers tested the theory in numerous modest studies over the years, often confirming that people who ate a lot of fiber had lower cancer rates than people who ate little. At the same time, some research failed to find an effect but received less publicity.

In the 1980s, the National Cancer Institute teamed with Kellogg’s, maker of All-Bran, to advertise the theory that eating fiber helped prevent cancer. After the ad campaign, surveys found that as many as one-third of people surveyed were aware of fiber’s cancer-fighting potential.

Today, the cancer institute advises Americans to “increase fiber” to 20 to 35 grams a day as part of its basic diet “geared to cancer prevention.”

Kellogg’s says on its Web site that “fiber may literally behave to protect against certain types of cancers--particularly colon cancer.”

Dr. Andrew Weil, a leader of the alternative health movement, says in a best-selling book to “eat a high-fiber diet to protect against colorectal cancer,” among other diseases.

Whether the new results will dent the appetite for high-fiber cereals remains to be seen. About 8% of those who purchased a high-fiber product did so in part to prevent colon cancer, according to a 1989 Prevention magazine survey. The Food Marketing Institute has found that about 3% of shoppers look for fiber on food package labels.

Cereal makers and other food producers downplayed the study, saying that it would have minimal impact on their marketing messages and in their consumers’ minds. “People eat these [high-fiber foods] for a variety of other reasons--it’s heart-healthy,” said Gene Grabowski, spokesman for the Grocery Manufacturers of America, which represents Kraft, Heinz and other firms. “One study is not a reason to overreact.”

Researchers Praise Study Methods

The new research draws on the massive Nurse’s Health Study, which began in 1976 when Harvard-affiliated researchers sent extensive health questionnaires to 121,700 female registered nurses. Over the years, researchers led by medical epidemiologist Walter Willett have correlated the nurses’ disease and death rates with various lifestyle factors, from body weight and diet to exercise and cigarette smoking.

For the latest analysis, the women were classified into five groups according to how much fiber the dietary questionnaires suggested they consumed each day, from a low of 10 grams to a high of 25.

Overall, the incidence of colorectal cancer did not vary, with 0.9% of the women in each group of about 17,700 women developing cancer in the 16 years of the study. The researchers also found the same rate of benign lesions, or polyps, in the women, regardless of fiber intake.

“It is a very good study,” said Geoffrey Howe, chairman of epidemiology at the Columbia University School of Public Health and co-author of a widely cited 1992 data review suggesting that a high-fiber diet seemed to prevent colon cancer.

But the new data outweigh the previous research, which was flawed because it was based largely on cancer patients’ long-term recollection of their dietary habits, he said.

Howe and other medical experts pointed out that diets that are high in fiber tend to include lots of fruits, vegetables and grains that may have other, as yet undiscovered, benefits. The federal recommendation to eat more of those foods and reduce fat intake remains sound advice, he said.

Times staff writers Stuart Silverstein and Jeff Leeds contributed to this story.