The first low carbohydrate diets for diabetes, which were introduced in the 18th century, were not high fat diets so much as high protein diets. By the late nineteenth century a consensus had begun to appear in European studies that a higher fat and lower protein intake was more tolerable. Frederick Allen confirmed this in animal studies, but the diet he introduced into clinical practice in 1914 restricted fat, protein, and total calories, becoming in extreme cases a starvation diet with the deadly side effect of “inanition”. Interpreting Allen’s research in light of the studies in chemical metabolism of Rollin Woodyatt, Louis “Harry” Newburgh, with Phil Marsh, dared to increase fat in the diets of diabetic patients at the University of Michigan Hospital in 1918, with gratifying results which were published in 1920. A dispute followed between Newburgh and Allen’s disciple Elliott P Joslin; Woodyatt, Russell M Wilder, Karl Petren and others confirmed Newburgh’s results by experimentation and by 1924 Joslin too was reporting the higher fat diet’s ability to extend life in diabetics untreated with insulin. However, a dispute between Joslin and Newburgh about the long-term safety of the high fat diet continued long into the insulin era. Because the debate about the effect of the high-fat diet in the tabula rasa of the pre-insulin era only lasted a few years, and rigorous research into the question was largely limited to the state of Michigan, medical history has paid little attention to the fact that the question of what is the “optimum”, or default, diet for diabetes, based on physiological principles as well as clinical practice and experiment, was at one time almost settled. This historical review paper summarises the early clinical researches of Newburgh et al. into the effects of the high-fat diet in the treatment of diabetes, with a particular focus on events in Michigan between 1918 and 1930.