Dr. Tim Johnson: The Fiber Failure

The latest research showing that fiber does not reduce the risk for colon cancer comes as a great disappointment to both medical scientists and all of us as consumers.

As medical scientists, we are always looking for relatively easy ways to prevent or treat serious problems. And as consumers, we are always pleased when a magic pill might be a magic bullet. But this time, it was not meant to be. How could we have become so enamored of the high-fiber hypothesis?

It all started with some old-fashioned medical sleuthing by Dr. Dennis Burkitt when he was working as a medical missionary in Africa. He connected two observations — that Africans had less colon cancer and ate more fiber than people in industrialized societies. (He also noticed that Africans had no problem with one of the major complaints in Western countries — so-called bowel irregularity. More about that later.)

However, as we learned more about how colon cancer almost always begins with small growths called polyps on the inner lining of the colon, we were able to study the role of fiber in preventing such polyps much more precisely. And, to make a long scientific story short, we now know that fiber does not seem to have any impact on preventing polyps and is therefore unlikely to have any impact on reducing colon cancer risk.

Do We Abandon Fiber?

Does that mean we should abandon fiber as “health food?” Absolutely not, in my judgment. For one thing, the stuff does work remarkably well in promoting regular bowel movements, no small matter in our “bowel-centric” society, where older people in particular are very concerned about regularity. There is also good evidence that dietary fiber might help reduce the risk for heart disease and diabetes.

But I believe this latest evidence does mean we should finally give up any hope that fiber will reduce the risk for colon cancer. Fortunately, we now know that polyps grow into actual cancer so slowly that if we detect them early, we can almost always prevent colon cancer by removing them. Which is why I now recommend regular colonoscopy exams for anyone over age 50 — and even sooner for anyone with a family history of colon cancer or a history of colon problems that increase the risk for cancer. So at the same time we have lost our faith in fiber, we must emphasize the good news — which is that colon cancer is theoretically almost 100 percent preventable through the use of existing screening tests.