I am reading the most amazing book, Good Calories Bad Calories by Gary Taubes. I've had this book for a while, but haven't had the time to read it. It is long and scientifically dense, and it challenges just about everything I thought I knew about nutrition. He has taken aim at the lipid hypothesis, salt intake, calories in and calories out, but I was floored when I read chapter 7 in the book on fiber.
In the early 1970's, a missionary surgeon named Denis Burkitt, proposed that fiber, the indigestible carbohydrate roughage, was an absolutely necessary element to a healthy diet. He claimed the absence of fiber in the diet was the reason behind diseases of civilization, those diseases that appeared wherever the Western diet, which was largely devoid of fiber, was consumed (e.g., diabetes, heart disease, high blood pressure, cavities, appendicitis, cancer, etc.). Burkitt publised his fiber hypothesis in the British journal The Lancet in 1972 and, with missionary zeal (Taubes describes it as "messianic" zeal), aggressively promoted the hypothesis. The media jumped on the fiber band wagon, and the belief that fiber would prevent colon cancer and other diseases of civilization became conventional wisdom.
There's just one small problem with this hypothesis: there is no empirical evidence to back up the fiber hypothesis. Says Taubes, "Over the last quarter-century, Burkitt's fiber hypothesis has become yet another example of Francis Bacon's dictum of "wishful science"--there has been a steady accumulation of evidence refuting the notion that a fiber-deficient diet causes colon cancer, polyps, or diverticulitis, let alone any other disease of civilization" (p. 132). Two Harvard studies, one of 49,000 male health professionals and another of 89,000 female nurses confirmed that increasing the fiber in the diet by eating more whole grains, fruits, and vegetables had no beneficial effect on colon cancer, nor did it prevent heart disease, breast cancer, or other diseases of civilization. A half dozen other, smaller studies also came to the same conclusions (see the notes for chapter 7 for references to the studies; I am traveling through Scotland as I write this and don't have the time to search online for the references). Gradually, a quarter century of studies has failed to support Burkitt's hypothesis, yet the belief that fiber is healthy remains alive. Apparently, it is just another load of CWOPO. Taubes does concede, however, that eating fiber helps with constipation.