In 1966, Burkitt returned to England, where he worked as a cancer epidemiologist for the Medical Research Council. There Richard Doll told him about Cleave and his saccharine-disease hypothesis. Burkitt met with Cleave and read Diabetes, Coronary Thrombosis and the Saccharine Disease, which he found revelatory. Cleave possessed “perceptive genius, persuasive argument and irrefutable logic,” Burkitt wrote.

What he was saying was that many of the common diseases in post-industrialized western countries are rare throughout the third world, were rare even in England or New York until about the First World War, are equally common in black and white Americans, and therefore must be due not to our skin color or our genes, but to the way we live. Now, this made an enormous amount of sense to me because I knew from my experience in Africa that he was perfectly right saying this.

On a tour of the United States, Burkitt visited hospitals and observed, as George Campbell had a decade earlier, that African-American patients in these hospitals were often obese, diabetic, or atherosclerotic, conditions virtually nonexistent among the black Ugandans Burkitt had treated.

Burkitt considered himself in the ideal position to test Cleave’s hypothesis on a wider scale. He had already established a network of 150 African hospitals, mostly missionary hospitals in rural areas, that mailed him monthly reports on their cancer cases: “I was able to ask them all: ‘Do you see gallstones, appendicitis, diverticular disease, coronary heart disease….’” Burkitt also sent his questionnaire to mission hospitals through out the world, and over eight hundred faithfully returned them. The results confirmed the basics of Cleave’s hypothesis. Whereas Cleave had anecdotal evidence, Burkitt recalled, he now had “anecdotal multiplied by a thousand,” and it was all consistent. Moreover, he had the necessary reputation to be taken seriously, whereas Cleave did not. Cleave, Campbell, and others had been “written off as cranks,” Burkitt said. “Now, just because there happened to be a Burkitt’s lymphoma, when Burkitt said, ‘What about looking at this,’ people listened to me when they hadn’t listened to far better guys.”

Through the early 1970s, Burkitt published a series of articles expanding on Cleave’s hypothesis. “These ‘western’ diseases are certainly associated geographically and in many instances tend to be related to one another in individual patients,” Burkitt wrote in the Journal of the National Cancer Institute in 1971. “My epidemiological studies in Africa and elsewhere substantiate Cleave’s basic hypothesis. Changes made in carbohydrate food may of course be only one of many etiological factors, but in some instances they would appear to be the major one.”