"Facts" on Fiber

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About three years ago, I started sprinkling a mixture of oat bran, wheat bran and wheat germ on my oatmeal every morning. Like many Americans, I'd heard about the studies linking a diet high in fiber--found in cereal grains, fruits and vegetables--to the prevention of heart disease and colon cancer. I figured I couldn't go wrong.

But it wasn't that simple. I quickly learned that you shouldn't shovel a lot of bran into your system all at once. You get bloated and gassy and suffer abdominal cramps from the sudden onslaught of all that indigestible bulk. Once I got over the initial discomfort, though, my new breakfast ritual became routine.

So am I going to tear up my morning menu now that two new studies reported last week in the New England Journal of Medicine suggest that fiber may not protect against colon cancer? Not on your life. There are lots of other reasons, backed by solid research, for eating a high-fiber diet. Among them: it lowers blood pressure, decreases the cholesterol level and lessens the chances of developing type II, or adult-onset, diabetes.

More than anything else, the reports show how little we understand about the ways diet affects health. In the larger of the two studies, Dr. Arthur Schatzkin of the National Cancer Institute and his colleagues recruited 2,079 men and women ages 35 and older who had had a precancerous polyp removed from their colon in the previous six months. (About 5% to 10% of such polyps eventually become malignant.) The volunteers were then randomly divided into an "intervention group," which ate a low-fat diet that included five to eight servings of fruits and vegetables each day, and a control group, which consumed more red meat, fewer beans and less fish.

After four years, the folks on the intervention diet had eaten an average of 35 g of fiber a day, against 20 g for their typical-fare counterparts. Yet both groups developed the same number of new polyps. A second nci study, involving 1,303 people ages 40 to 80, divided into high-fiber and low-fiber groups, produced similar results.

Even if fiber doesn't inhibit polyps, it may still help prevent colon cancer. Maybe you have to eat a lot more fiber-rich fruits and vegetables to get any benefit. Maybe you have to eat right and exercise more. Maybe you have to eat a healthy diet for a long time. ("Think of it this way," says Dr. Steven Zeisel, a nutrition expert at the University of North Carolina, Chapel Hill, who was not involved in either study. "When you stop smoking, you don't immediately lower your risk of lung cancer. It can take 10 years to see a difference.") Or maybe fiber doesn't prevent colon cancer.

Whatever the case, it makes sense to concentrate on what doctors know for sure about colon cancer, which is that early detection saves lives. So get screened, starting at least by age 50 (earlier if you have a family history of the cancer). The simplest tests look for blood in the stool. The more involved tests examine the entire length of the colon for suspect lesions.

As for those fruits and vegetables, keep eating them. Mom told you they were good for you, and maybe some day researchers will be able to tell you why.

You can e-mail Christine at gorman@time.com