Background
The worldwide population of individuals with diabetes is more than 382 million people, and potentially, 20.5 million of these are in Japan. Because the subsequent ischemic heart disease, cerebral infarction, retinopathy, nephropathy, and neuropathy are life threatening to numerous people, the prevention of diabetes is of great importance. Among many environmental factors associated with diabetes, obesity is a particularly well-known risk factor for type 2 diabetes. Notably, studies indicate that East Asian individuals with body mass indexes (BMIs) within normal range are much more likely to develop diabetes compared with Caucasians and African Americans with those BMIs.
Several studies have indicated that individuals with high BMIs are at a high risk of developing diabetes,; however, due to their cross-sectional or 2–3 time-point cohort designs, these reports have not distinguished the risk of "increasing BMI" on diabetes onsets from that of "high BMI per se." The present study from Japanese large-scale clinical data was driven by the interest in comparing BMI trajectories in diabetic patients and healthy individuals and by the question of whether increasing BMI alone would cause diabetes.