Good Calories, Bad Calories

As we have seen with other hypotheses, the belief that dietary fiber is an intrinsic part of any healthy diet has been kept alive by factors that have little to do with science: in particular, by Geoffrey Rose’s philosophy of preventive medicine—that if a medical hypothesis has a chance of being true and thus saving lives, it should be treated as if it is—and by the need to give the public some positive advice about how they might prevent or reduce the risk of cancer. This was immediately evident in a New England Journal of Medicine editorial that accompanied back-to-back April 2000 reports on two major trials—one on fourteen hundred subjects of the Phoenix [Arizona] Colon Cancer Prevention Physicians’ Network, and one $30 million trial from the National Cancer Institute—both of which confirmed that fiber had no effect on colon cancer. The editorial was written by Tim Byers, a professor of preventive medicine at the University of Colorado, who said that the two trials had been short-term and focused only on the early stages of cancer. For this reason, they should not be interpreted as “evidence that a high-fiber cereal supplement or a low-fat high-fiber diet is not effective in protecting against the later stages of development of colorectal cancer.” Byers was wrong, in that the results certainly were evidence that a high-fiber diet would not protect against the later stages of colorectal cancer; they simply weren’t sufficient evidence for us to accept the conclusion wholeheartedly as true.

Burkitt’s hypothesis lived on, and it would continue to live, as the fat/ breast-cancer hypothesis continued to live on, in part because the original data that led to it remained unexplained: “Observational studies around the world,” wrote Byers, “continue to find that the risk of colorectal cancer is lower among populations with high intakes of fruits and vegetables and that the risk changes on adoption of a different diet, but we still do not understand why.” It would always be possible to suggest, as Byers had, that the trials could have been done differently—for longer or shorter duration, on younger subjects or older subjects, with more, less, or maybe a different kind of dietary fiber—and that the results would have been more promising. The American Cancer Society and the National Cancer Institute continued to suggest that high-fiber diets, high in fruits and vegetables, might reduce the risk of colon cancer, on the basis that some evidence existed to support the hypothesis and so a prudent diet would still include these ingredients.

The media would also contribute to keeping the fiber hypothesis alive, having first played a significant role in transforming Burkitt’s hypothesis into dogma without benefit of any meaningful long-term clinical trials. “Scientists have known for years that a diet rich in vegetables, fruits and fiber, and low in fat, can greatly reduce—or eliminate—the chances of developing colon cancer,” as a 1998 Washington Post article put it—four years after the Harvard analysis of forty-seven thousand male health professionals suggested it was not true.

Although the New York Times ran articles on the negative results from the Nurses Health Study (by Sheryl Gay Stolberg) and the Phoenix and NCI fiber trials (by Gina Kolata), neither was written by the two reporters who had followed the subject for decades and traditionally wrote about diet and health for the paper: Jane Brody, who wrote the Times personal-health column, and Marian Burros, who had begun endorsing the benefits of fiber as a Washington Post reporter in the 1970s and had joined the Times in 1981. Rather, Burros and Brody chose to respond to the negative news about Burkitt’s hypothesis by continuing to defend it with the fallback position that it still might be true in other ways. “If preventing colon cancer was the only reason to eat fiber,” wrote Jane Brody after the publication of the Phoenix and NCI studies, “I would say you could safely abandon bran muffins, whole-grain cereals, beans and peas and fiber-rich fruits and vegetables and return to a pristine diet of pasty white bread. But dietary fiber…has myriads of health benefits.” After Stolberg’s 1999 report on the Nurses Health Study, the Times published an article by Brody entitled “Keep the Fiber Bandwagon Rolling, for Heart and Health,” pointing out that fiber was certainly good for constipation and that earlier results from the Nurses Health Study had suggested that women who ate “a starchy diet that was low in fiber and drank a lot of soft drinks developed diabetes at a rate two and a half times greater than women who ate less of these foods.” This, according to Brody, constituted the motivation to keep fiber in a healthy diet.