Sugar and white flour were also obvious suspects in the etiology of diabetes, because the dramatic increase in consumption of these foodstuffs in the latter decades of the nineteenth century in the United States and Europe coincided with dramatic increases in diabetes incidence and mortality. Unlike heart disease, diabetes was a relatively straightforward diagnosis. After the introduction of a test for sugar in the urine in the 1850s, testing for diabetes became ever more common in hospitals and life-insurance exams, and as life insurance itself became popular, physicians increasingly diagnosed mild diabetes in outwardly healthy individuals, so the incidence numbers rose. As with coronary heart disease, the diagnostic definition of diabetes changed over the years, as did the relevant statistical analyses, so no conclusions can be considered definitive.

Nonetheless, the numbers were compelling. In 1892, according to William Osler in Principles and Practice of Medicine, only ten diabetics had been diagnosed among the thirty-five thousand patients treated at Johns Hopkins Hospital. At Massachusetts General Hospital in Boston, only 172 patients had been diagnosed as diabetic out of nearly fifty thousand admitted between 1824 and 1898; only eighteen of those were under twenty years old, and only three under ten, suggesting that childhood diabetes was an extremely rare diagnosis. Between 1900 and 1920, according to Haven Emerson, director of the Institute of Public Health at Columbia University, the death rate from diabetes, despite improved treatment of the disease, had increased by as much as 400 percent in American cities. It had increased fifteen-fold since the end of the Civil War. Emerson reported proportional increases in diabetes mortality in Great Britain and France and suggested they were due to the increased consumption of sugar, combined with an increasingly sedentary lifestyle. Moreover, diabetes rates had dropped precipitously during World War I in populations that had faced food shortages or rationing. “It is apparent,” wrote Emerson in 1924, “that rises and falls in the sugar consumption are followed with fair regularity within a few months by similar rises and falls in the death rates from diabetes.”

The hypothesis that sugar and refined carbohydrates were responsible might have survived past the 1930s, but Elliott Joslin refused to believe it, and Joslin’s name was by then “synonymous” with diabetes in the United States. Joslin may once have ranked beneath Frederick Allen in the hierarchy of American diabetologists, but Allen’s reputation had been built on his starvation cure for diabetes, which was only marginally effective, and rendered unnecessary once insulin was discovered in 1921. Joslin achieved lasting fame by pioneering the use of insulin as a treatment. From the 1920s onward, Joslin’s textbook The Treatment of Diabetes Mellitus and his Diabetic Manual were the bibles of diabetology.