It was precisely this work that led to the fiber hypothesis and its present place in our nutritional consciousness. In 1972, Burkitt and Walker published an article in The Lancet supporting their theory and discussing their measurements of transit time and stool characteristics in twelve hundred human subjects. In rural areas, unaffected by industrialization, they reported, “diets containing the natural amount of fiber are eaten and result in large, soft stools that traverse the intestine rapidly. By contrast, the refined low-fiber foods of the economically-developed countries produce small firm stools which pass through the gut very slowly.” Thus, the relative constipation endemic in the developed world, they suggested, appeared to play a causative role in bowel-related disorders: appendicitis, diverticulitis, and both benign and malignant tumors of the colon and rectum, all of which showed the classic distribution of diseases of civilizations. “All these diseases are very closely associated epidemiologically,” Burkitt and Walker explained. “These diseases are still rare in developing countries and in rural Japan, where eating habits have changed but little, but they are all seen increasingly in Japanese who live in Hawaii and California and are increasing in Japan in those who have changed to a Western diet. In no country or region is one of these diseases common and the others rare save that appendicitis, which afflicts the young, appears about a generation before the other conditions.”

Within two years, Burkitt had extended his hypothesis from appendicitis, diverticulitis, and colon cancer to all chronic diseases of civilization. In the process, Cleave’s refined-carbohydrate hypothesis of saccharine diseases was transformed into Burkitt’s fiber hypothesis of Western diseases. This transformation of the causal agent of disease from the presence of carbohydrates to the absence of fiber may have been influenced by factors other than science—Burkitt’s close association with Harold Himsworth in particular. Himsworth had been secretary of the Medical Research Council when Burkitt was hired, and he had been publicly effusive about Burkitt’s contributions to modern medicine. It was Himsworth’s research that had been responsible for convincing diabetologists that sugar and other carbohydrates were not the cause of diabetes. Indeed, Cleave and Campbell had presented their saccharine-disease theory in the context of diabetes as a refutation of Himsworth’s scholarship as much as Joslin’s. That Burkitt would find Cleave’s general thesis compelling but the details unacceptable in light of Himsworth’s own work and beliefs is quite possible. Burkitt would often tell the story of how Himsworth had convinced him of the importance of paying attention to those factors that were absent in searching for the causative agents of disease. “Denis,” Burkitt recalled Himsworth telling him, “do you remember the story in Sherlock Holmes when Holmes said to Watson: ‘The whole clue, as I see it, to this case lies in the behavior of the dog.’ And Watson said: ‘But, sir, the dog did nothing at all.’ ‘That,’ said Holmes, ‘is the whole point.’ And it often is in medicine…. The clue can lie in what is not there rather than what is there.” In this case, fiber was not there. Burkitt also seemed motivated by the simple expediency of emphasizing the positive benefits of fiber rather than the negative effects of sugar and flour, which seemed like a hopeless cause. “[Sugar] is simply an integral part of the daily diet and emphatically is here to stay,” Burkitt’s collaborator Alec Walker said. Better to say Don’t Forget Fibre in Your Diet, which was the title of Burkitt’s 1979 diet book, than to say, Don’t eat sugar, flour, and white rice, and drink less beer.