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High-fiber diet does not reduce colon cancer risk, studies say


ATLANTA -- A high-fiber diet does not prevent the polyps that can lead to colorectal cancer, according to two large studies published in this week's New England Journal of Medicine (NEJM).

Each year 130,000 Americans are diagnosed with colorectal cancer, and 56,000 die from the disease. Previous research suggested a high-fiber diet could reduce a person's risk, but those studies did not directly measure the anti-cancer effects of a high-fiber diet.

"There may be many reasons to eat a diet that is low in fat and high in fiber, fruits, and vegetables or to supplement the diet with a food high in cereal fiber, but preventing colorectal adenomas, at least for the first three to four years, is not one of them," said Dr. Tim Byers of the University of Colorado School of Medicine in an accompanying editorial.

The doctors in both NEJM studies used colorectal adenomas -- polyps that can turn into tumors -- to gauge the effectiveness of a high-fiber diet. Polyps were used because they appear faster, while colorectal cancer itself can take years to develop.

In the first study, conducted at the National Cancer Institute (NCI), researchers put 958 people on a low-fat, high-fiber, high-fruit and vegetable diet. Another 947 people were given information on how to eat healthy and were told to follow their usual diets.

All the participants had had at least one precancerous polyp removed in the six months prior to the study, and therefore had a higher than normal risk of colorectal cancer.

After four years, researchers found the risk of developing another polyp was the virtually the same in both groups.

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    Source: WebMD

    The second study, led by David S. Albers of the Arizona Cancer Center, had similar findings.

    As part of that study, 719 people ate half an ounce of wheat bran fiber each day and another 584 ate less than a tenth of an ounce.

    Colonoscopies conducted after three years showed the risk of developing a polyp was the virtually the same in both groups.

    But the study authors expressed concern that three years may have not been enough time to see a difference in the two groups. However, there have also been two other studies which did not find cereal fiber to reduce risk of colon cancer. These were the Nurses' Health Study and the Health Professionals' Follow-up study.

    Researchers had been hopeful there was a connection between high-fiber diets and a reduction in the risk of colon cancer. Studies outside the U.S. had found colorectal cancer rates to be lower in places where people consumed more fruits and vegetables, and higher in people from those areas who changed to diets higher in fat and lower in fiber.

    Byers, in his editorial, said, the new research shows, "we still do not understand why."

    But experts say people shouldn't give up on high-fiber, low-fat diets just yet. This type of diet is still recommended for overall health and disease prevention.

    "All it (the NCI study) says is that at one stage over a four year period of time the diet had no effect. Now cancer, particularly colon cancer, may take 15 years to develop. We don't know the effect of diet on the other stages of the cancer," said Dr. Moshe Shike of Memorial Sloan-Kettering Cancer Center.

    A high-fiber diet can reduce the risk of heart disease, high blood pressure, and diabetes.

    The American Institute of Cancer Research (AICR) reacted to the NCI study saying these newest findings, "should not prompt people to abandon diets that have been consistently linked to reducing the risk of colon cancer."

    Because the average age of NCI study participants was 61, AICR spokeswoman Ritva Butrum said the findings may simply show dietary changes need to be made early in life.

    CNN Medical Correspondent Dr. Steve Salvatore and Reuters contributed to this report.

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    March 2, 1999
    High-fiber diet doesn't reduce colon cancer risk, study finds
    January 20, 1999
    Genetic discovery may lead to early colon cancer detection
    November 2, 1998
    Adding more calcium to your diet may reduce the risk of colon cancer
    September 22, 1998

    American Institute of Cancer Research (AICR)
    American Cancer Society
    National Cancer Institute
    Cancer Information Service
    Arizona Cancer Center

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