Fiber diet fails to prevent colon cancer, study finds

A major colon cancer prevention study has failed to find any evidence that a high-fiber, low-fat diet can protect a person from the deadly disease. <br><br>Although its cancer-fighting benefits are touted

Monday, April 24th 2000, 12:00 am

By: News On 6

A major colon cancer prevention study has failed to find any evidence that a high-fiber, low-fat diet can protect a person from the deadly disease.

Although its cancer-fighting benefits are touted on cereal boxes and bread wrappers, a high-fiber diet didn't prevent formation of polyps - small buds of tissue that can morph into tumors. The study enrolled people with a history of polyps who were at risk of developing more of the growths.

"We're very disappointed," said Dr. Arthur Schatzkin of the National Cancer Institute, who led the study. The research, estimated to cost at least $25 million, was described Thursday in The New England Journal of Medicine.

A smaller study published in the journal, from scientists at the University of Arizona, also found that eating high-fiber cereal every day failed to prevent polyps from reappearing. The study, of about 1,300 adults, examined the effect of adding more than 10 extra grams of dietary fiber a day. (One cup of Raisin Bran has about 8 grams.)

Researchers were surprised by the findings but stressed that the results don't mean that people should abandon a diet rich in fruits and vegetables and low in fat. There are many reasons the study could have failed to find any benefit, and there are other ways that fruits and vegetables can prevent disease, they said.

"To go out and say everyone should eat cheeseburgers is not correct," said Dr. Bernard Levin, a colon cancer expert from the University of Texas M.D. Anderson Cancer Center in Houston, who was not involved in the research. A diet emphasizing fruits and vegetables "is probably good for heart disease, weight control; it may be helpful for diabetes."

But not, it seems, for colon cancer.

Until recently, most evidence that fiber protects against colon cancer had come from animal experiments and observations of people who seemed somehow protected from the malignancy.

For example, people who live in countries with low-fat, high-fiber diets have some of the lowest rates of colon cancer in the world. Yet, when those people migrate to countries such as the United States, their colon cancer rates soar. Also, as the fat consumption in certain countries has risen, so has the frequency of colon cancer.

Experts have offered theories to explain this. Fiber may speed up digested food's journey through the intestine, they said, perhaps reducing the body's exposure to cancer-causing compounds. Fat, on the other hand, is thought to produce harmful compounds during digestion.

To prove an actual cause and effect in humans, researchers began a nationwide study in the early 1990s, recruiting more than 2,000 volunteers from eight sites. Half the participants were given intense counseling and support to lower the amount of fat they ate, and to increase the amount of fiber, fruits and vegetables. Each person was followed for four years.

In the end, the changes in diet did not decrease the number of polyps. That doesn't necessarily mean, however, that fiber is useless in the fight against colon cancer.

"It's hard to extrapolate to the whole of colon cancer," M.D. Anderson's Dr. Levin said.

The people in the study might simply not have changed their eating habits enough to make a difference. After four years, they were getting about 24 percent of their calories from fat - compared with 34 percent of calories from fat in the comparison group - but the number may have to fall even lower, scientists said.

Or, suggested Dr. Tim Byers of the University of Colorado School of Medicine, perhaps four years wasn't long enough to detect any effect.

"I think the more important question is whether those kinds of diet changes might have made a difference later," he said.

Dr. Byers was not involved in the research, but he wrote an editorial published with the new study.

Colon cancer may simmer for decades before it shows itself. For that reason, a fraction of the people in the experiment will continue to be watched. Fiber could also make a difference early in life, before polyps develop for the first time. This, too, wasn't studied in the experiment.

Meanwhile, Dr. Byers said, "For people who want to prevent colon cancer, I think we're back to what works. That is, find and remove polyps." Only about 5 percent to 10 percent of polyps lead to cancer if they are not removed, but physicians can't tell which ones are harmful.

Dr. Elena MartÃnez, one of the scientists who conducted the cereal study, said doctors had embraced the notion that fiber could protect against colon cancer because the idea sounded plausible and easy to adopt. Along with other researchers, she will now advise patients to direct their colon cancer prevention efforts back to regular checkups.

"If everybody would get screened, we wouldn't have to worry about colon cancer," said Dr. MartÃnez, who is from the Arizona Cancer Center in Tucson. Doctors recommend that people begin screenings for the cancer at age 50, or earlier if certain risk factors, including family history of the disease, are present.

Although the case for cereal fiber has crumbled, she said she still believes that vegetables may be important for colon-cancer prevention and should be investigated further.

Colon cancer remains the second-most-common cancer killer among Americans, she said. "We have to keep trying to find the clues for this disease."