But Burkitt was beginning to revise Cleave’s hypothesis. Now Burkitt’s working assumption, as he explained in the JNCI, was that any dietary factors responsible for benign conditions such as appendicitis or diverticulitis were likely to be responsible as well for related malignant conditions—in particular, colon and rectal cancer. Burkitt’s research had led him to Thomas Allinson, who in the 1880s argued that white flour caused constipation, hemorrhoids, and other ills of modern societies. It also led him to a 1920 article by the Bristol University surgeon Arthur Rendle Short, documenting a dramatic increase in the incidence of appendicitis that Rendle Short also blamed on white flour and the lack of fiber in modern diets. Burkitt believed he could draw a direct line of causation from the absence of fiber in refined carbohydrates to constipation, hemorrhoids, appendicitis, diverticulitis, polyps, and finally malignant colon and rectal cancer.

Burkitt’s African correspondents had reported that appendicitis increased dramatically in urban populations—at Burkitt’s Mulago Hospital in Kampala, the number of yearly appendectomies had increased twenty-fold from 1952 to 1969—whereas polyps, diverticular disease, and colorectal cancer, all common in the United States and Europe, wrote Burkitt, were still “very rare in Africa and almost unknown in rural communities.” Burkitt concluded that appendicitis, just as it appeared in Western nations typically in children, appeared in Africans, both adults and children, within a few years of the adoption of Western diets.

Burkitt focused now on constipation. He theorized that removing the fiber from cereal grains would slow the “transit time” of the stool through the colon. Not only would any carcinogens in the stool therefore have more time to inflict damage on the surrounding cells, but it was conceivable that the overconsumption of refined carbohydrates would increase the bacterial flora of the stool, and that in turn could lead to carcinogens being metabolized by the bacteria out of “normal bowel constituents.” Burkitt could offer no explanation for why this might cause appendicitis, but he was confident that some combination of all these factors played a role.