What causes cancer? In 2015, researchers updated the landmark 1981 study from the U.S. Congress Office of Technology Assessment noting that the original estimates had “generally [hold] true for 35 years.” At 35% of the attributable risk, tobacco was the single largest contributor to cancer. But very close behind, was our diet, which researchers estimated contributed between 30–60% of the risk. Generally accepted as true, the far more contentious question is “What part of the diet contributed to the risk of cancer?”
The legendary Irish surgeon Denis Burkitt noted in 1973 that many diseases characteristic of modern Western civilization were noticeably absent where he worked in rural Africa. Cancer, specifically colorectal cancer was one of these diseases. Burkitt hypothesized that diet was the main differentiating factor, and specifically, the fiber. The traditional African diet contained a lot of fiber — a lot. This bulked up the stool, leading to frequent and large-volume bowel movements. Big lush piles of poo. Not the measly, rabbit pellet stools of the European ex-pats. Perhaps the regular movement of the stool cleared the intestinal system, preventing decaying and putrefying of foods inside the colon, which might be carcinogenic. The high stool volume meant frequent “cleansing” bowel movements. Eating more fiber was enthusiastically championed as an easy way to improve health and reduce cancer. From the 1970s to the early 2000s, people heartily ate more ‘roughage’ in the hopes of preventing cancer. But those efforts were largely futile.
By the mid 1990s, studies established that eating more dietary fiber played little or no role in reducing the risk of colon cancer. The Nurse’s Health Study, with over 88,000 women over 16 years of follow up, found that those women eating the most fiber had essentially risk of cancer as those eating the least. Other studies were equally discouraging. The Toronto Polyp Prevention Group, the Australian Polyp Prevention Project, and a randomized controlled trial published in year 2000 in the New England Journal of Medicine all confirmed that a high fiber diet did not reduce cancer.