The evidence that led Peter Cleave to propose this alternative theory—the disparity in disease rates among populations, the intimate relationship of atherosclerosis, hypertension, obesity, and diabetes, and the apparent absence of chronic disease in populations relatively free of Western influences—had to be explained in other ways if they were to be consistent with Keys’s hypothesis. Fiber, the indigestible carbohydrates in vegetables, starches, and grains, now replaced refined carbohydrates and sugar in the debate about the nutritional causes of chronic diseases. The fiber hypothesis captured the public’s nutritional consciousness by virtue of the messianic efforts of a single investigator, a former missionary surgeon named Denis Burkitt, who proposed that this indigestible roughage was a requisite component of a healthy diet. The notion was consistent with Keys’s hypothesis, which was not the case with Cleave’s or Yudkin’s hypothesis, and it resonated also with the era’s countercultural leanings toward diets heavy in vegetables, legumes, and cereal grains.

Burkitt’s fiber hypothesis was based originally and in its entirety on Cleave’s saccharine-disease hypothesis, but simply inverted the causal agent. Rather than proclaim, as Cleave did, that chronic disease was caused by the addition of sugar and refined carbohydrates to diets that we had evolved naturally to eat, Burkitt laid the blame on the subtraction of the fiber from those evolutionarily ideal diets, which in turn led to constipation and then, through a variety of mechanisms, all the chronic diseases of civilization. The fiber deficiency itself was caused either by the removal of fiber during the refining of carbohydrates or by the consumption of refined carbohydrates in lieu of the fibrous, bulky roughage we should be eating. The fiber hypothesis and the refined-carbohydrate hypothesis of chronic disease were photographic negatives of each other, and yet the fiber hypothesis caught on immediately upon appearing in the journals. The refined-carbohydrate hypothesis, which was the only one of the two that was capable of explaining the actual evidence, remained a fringe concept.

Denis Burkitt began his career as a missionary surgeon in Uganda in 1947. In the early 1960s, he earned his renown—“one of the world’s best-known medical detectives,” as the Washington Post would call him—for his studies of a fatal childhood cancer that came to be known as Burkitt’s lymphoma and would be the first human cancer ever linked to a viral cause. That discovery alerted Burkitt to the lessons to be learned by tracking the geographical distribution of disease. Burkitt spent five years gathering information about the lymphoma from hundreds of African hospitals, and made a legendary ten-thousand-mile, sixty-hospital trek from Kampala to Johannesburg and back as part of his research.