Investigative Analysis

The Truth About Fiber and Colon Cancer

May 2003

It would seem the medical establishment might have to flip-flop yet again regarding fiber intake and its preventative effect on colon cancer. Years of educated assumptions proclaiming the protective attributes fiber consumption had on colon cancer went by the wayside after a series of high-profile studies failed to show any tangible preventative benefits. Fiber, it was determined, while assuredly health-friendly, did not possess any cancer-preventing qualities. Some studies even went so far as to state people were more likely to develop colon cancer by eating fiber. This negative conception of fibers' protective powers has been commonplace for the better part of the past half-decade. That was until recently, when the British health journal The Lancet released the results of not one but two new studies on fiber consumption and its affect on the body.

What did the studies discover?

The first study, conducted by the National Cancer Institute, charted the eating and health habits of nearly 34,000 American subjects, 3,600 of whom showed precancerous growths in the colon. The findings showed those with "high intakes of dietary fiber were associated with a lower risk of colorectal adenoma, after adjustment for potential dietary and non-dietary risk factors. Participants in the highs quintile of dietary (intake of roughly 36g of fiber each day) fiber intake had a 27% lower risk of adenoma that those in the lowest quintile (roughly fewer than 12g per day)." The researchers concluded that, "dietary fiber, particularly from grains, cereals, and fruits, was associated with decreased risk of distal colon adenoma."

At roughly the same time that doctors from the United States were making their discoveries, a similar study on a much grander scale was being conducted in Europe. In what is thought to be the single largest study on cancer in recorded history, researchers studied 520,000 citizens (1065 of whom had developed colon cancer) in 10 European countries for the potential preventative benefits of fiber on colon cancer. This study also originally found a 25% reduced rate in colorectal cancer among those whose diets included roughly 35g of fiber a day, compared to those eating less than 15g. Upon further analysis, researchers discovered, "In populations with low average intake of dietary fiber, an approximate doubling of total fiber intake from foods could reduce the risk of colorectal cancer by 40%." Beyond that, the study of Europeans showed that the greatest protective effect was on the left side of the colon, where most cancer originates.

Ulrike Peters of the U.S. National Cancer Institute and head of the American study said, "these two new findings show the fiber hypothesis is alive."

Lead researcher of the British study, Sheila A. Bingham PhD stated, "and in our study, the people eating the most fiber were consuming as much dietary fat as those eating the lowest amounts and they still got the protective effects."

What this means for you

While the optimism among experts remains guarded, these findings should only encourage any concerted efforts made by the public to include healthy amounts of fiber in their diet.

Both studies demonstrate that those seeking protection from colon cancer averaged at least 30g of fiber in a day. The Washington Post reports Americans consume an average of 16g of fiber a day. The individuals in the studies receiving the most fiber protection averaged roughly 35g of fiber daily. A banana contains 3g of fiber. An apple was 3.5g, the same as a cup of brown rice. Some super-high fiber breakfast cereals have as much as 14g per half cup serving.

Lancet 2003; 361:1491-1495

Lancet 2003; 361:1495-1501

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