Colon cancer: clues to fiber's benefits.

Colon cancer: Clues to fiber's benefits

Among the deadly malignancies, colorectal cancer ranks second only to lung cancer in U.S. incidence and mortality. Though dozens of epidemiologic studies have linked its occurrence to diet -- and especially to foods low in fiber -- researchers know little about how fiber might affect cancer development. Now, a small study of people at high risk of colorectal cancer offers some potentially important clues.

The three-month study of breakfast cereals involved 11 women and six men who had portions of the colon or rectum removed during cancer surgery one to eight years earlier. The first month's daily cereal portions included only 2 grams of fiber; all later servings contained 13.5 grams. However, the low- and high-fiber 2/3-cup rations looked and tasted identical, the researchers say.

Colorectal cancer survivors "have an extremely high recurrence rate" of up to 40 percent, notes study director David S. Alberts at the Arizona Cancer Center in Tucson. The rectal surface cells of people at high risk of developing colorectal cancer also tend to proliferate at an abnormally rapid rate.

To measure the proliferation of these cells, Alberts and his co-workers biopsied tissue from each volunteer at the end of the first month (baseline) and again at the end of the third month. They incubated the tissue samples with tritium, a radioactive form of hydrogen. The degree to which DNA incorporated the tritium provided a gauge of the rate at which each batch of biopsied cells grew.

In the Aug. 1 JOURNAL OF THE NATIONAL CANCER INSTITUTE, the team reports that high-fiber cereal induced a dramatic and statistically significant reduction in cell proliferation among patients with a rapid baseline rate. The same cereal did not affect rectal-cell turnover in people with an initially low proliferation rate.

The decrease seen among patients who had the highest initial proliferation rates "hints that the fiber is effective in inhibiting whatever stimulates cancer in the colon," comments Jerome J. DeCosse at New York (City) Hospital. It not only "gets you closer to understanding the mechanism" behind fiber's inhibition of colorectal cancer, says Peter Greenwald of the National Cancer Institute, but also provides "clinical evidence that changing your diet may have some effect [on cancer risk] within a fairly short period."

Alberts' group is just finishing a 100-patient follow-up study on fiber and calcium -- another potential inhibitor of colorectal cancer. And on July 1, he began a fiber-treatment trial involving 1,400 people with colorectal polyps, a precancerous abnormality.