Development of diabetes in obese, insulin-resistant mice: Essential role of dietary carbohydrate in beta cell destruction

Aims/hypothesis: The role of dietary carbohydrate in the pathogenesis of type 2 diabetes is still a subject of controversial debate. Here we analysed the effects of diets with and without carbohydrate on obesity, insulin resistance and development of beta cell failure in the obese, diabetes-prone New Zealand Obese (NZO) mouse. Materials and methods: NZO mice were kept on a standard diet (4% [w/w] fat, 51% carbohydrate, 19% protein), a high-fat diet (15, 47 and 17%, respectively) and a carbohydrate-free diet in which carbohydrate was exchanged for fat (68 and 20%, respectively). Body composition and blood glucose were measured over a period of 22 weeks. Glucose tolerance tests and euglycaemic-hyperinsulinaemic clamps were performed to analyse insulin sensitivity. Islet morphology was assessed by immunohistochemistry. Results: Mice on carbohydrate-containing standard or high-fat diets developed severe diabetes (blood glucose >16.6 mmol/l, glucosuria) due to selective destruction of pancreatic beta cells associated with severe loss of immunoreactivity of insulin, glucose transporter 2 (GLUT2) and musculoaponeurotic fibrosarcoma oncogene homologue A (MafA). In contrast, mice on the carbohydrate-free diet remained normoglycaemic and exhibited hyperplastic islets in spite of a morbid obesity associated with severe insulin resistance and a massive accumulation of macrophages in adipose tissue. Conclusions/interpretation: These data indicate that the combination of obesity, insulin resistance and the inflammatory response of adipose tissue are insufficient to cause beta cell destruction in the absence of dietary carbohydrate.