Healthnotes Newswire (June 28, 2001)—Just when researchers were beginning to give up on fiber for the primary prevention of colon cancer, the largest study ever conducted on diet and cancer has once again turned the tables in the ongoing debate, giving fiber renewed clout as a cancer fighter. Although some previous studies have found no protective effect, initial results from the European Prospective Investigation of Cancer (EPIC) study show strong protective effects of dietary fiber on prevention of colon and rectal cancer.¹

According to Dr. Sheila Bingham, lead researcher of the EPIC working group on colorectal cancer, those at lowest risk for colon cancer ate an average of 50% more fiber in their diets than those at highest risk.² These findings are consistent with the observation that the standard diet in developed countries is deficient in fiber and that most Americans and Europeans could benefit from eating approximately 50% more fiber from whole grains, vegetables and fruit than they now consume. As in previous studies, EPIC participants who ate more processed meat were at increased risk for colon cancer.

EPIC Study

The EPIC is the largest study of diet and health ever undertaken. It involves over half a million people in ten European countries. By studying a great many people in different countries with differing diets, using carefully designed and tested questionnaires, EPIC is expected to produce much more detailed information about the effect of diet on long-term health than previous studies. The EPIC was initiated in 1992, and the first results began to appear in various medical publications in 2000. Details of the new study on fiber and colon cancer are not yet published.

The Ongoing Fiber Saga

Ever since Dr. Dennis Burkitt first proposed in 1971 that a high-fiber diet protects against colon cancer,³ researchers have been endeavoring to prove or disprove the link. There are many good reasons to think that increasing fiber consumption would decrease the risk of colon cancer. Fibers, such as wheat bran, can latch onto carcinogens (cancer-causing chemicals) from the bowel and facilitate their elimination.⁴ They can also bind to and increase the elimination of bile acids, which might otherwise promote damaging, and possibly cancer-promoting, changes in the walls of the intestines.⁵ In a population study, eating more cereal grains (high in fiber) was associated with a decreased risk of dying from colon cancer.⁶ A detailed analysis of multiple studies found a 42% decrease in the risk of colon cancer in people eating the most dietary fiber compared to those eating the least.⁷

Last year, a double-blind trial of fiber supplementation to prevent colorectal adenomas (a pre-cancerous condition of the colon) cast a doubt on those findings.⁸ In this trial, women and men with a history of colorectal adenoma who took high amounts of dietary fiber supplements (13.5 g of wheat bran per day for three years) had no more protection against recurrence of the adenomas than did those taking low amounts dietary fiber supplements (2 g of wheat bran per day for three years). There are plausible explanations of why a negative result was obtained in this trial: the difference in fiber intake between the two groups was probably not large enough to demonstrate an effect; compliance with the treatment regimen, particularly in the high-fiber group, was poor; and the length of the follow-up period may have been inadequate.

Nevertheless, the results of this trial were consistent with those of two similar trials^{9 10} and are further validated by two population studies that found no protective effect of high dietary fiber against colon cancer.^{11 12}

What explains the contradictory findings among the various studies? In studies showing high dietary fiber consumption was protective, the fiber may only have been a marker for other protective factors in the diet (e.g., folic acid). Another important argument, for which there is considerable evidence, is that eating less meat may confer protection against colon cancer. A diet low in red meat is a common characteristic of people who eat high amounts of fiber. Even in people who eat low amounts of fiber, a low intake of meat may protect against colon cancer.¹³ Nonetheless, the data from the EPIC study showed a strong protective effect from dietary fiber, independent of the moderately negative effect of red meat consumption.

According to a previous study by Professor Dr. Bingham, nearly 80% of breast, prostate, and colorectal cancers have been linked to dietary habits.¹⁴ Increasing dietary fiber may not provide a complete solution for colon cancer prevention, but it is clear that both high dietary fiber intake and intake of fiber supplements offer numerous other health benefits, especially in the cardiovascular system and in the lower digestive tract. According to Dr. Bingham, “People wishing to reduce their risk of colon cancer should consume more fiber in their diets.”