In Japanese type 2 diabetes, which occupies more than 95%, it is an increasingly important problem as a life-style related disease. The total diabetic population is estimated as approximately 7 million with a prevalence of approximately 6%. Along with genetically low postprandial insulin secretion, they are found to be less tolerable to being overweight to develop insulin resistance. The body weight change in the prediabetic era consisting of 508 male patients treated on their diet alone was reviewed and it was found that a few kilograms of weight gain could be a cause of insulin resistance. Moreover, inactive aldehyde dehydrogenese 2 (ALDH2), which is common in Japanese, is found to be a factor in the development of hyperglycemia. In 163 diabetics, HbAlc of the inactive ALDH2 group was 8.1+/-1.3, while that of active ALDH2 was 7.5+/-0.9% (P<0.05) in a light, social drinking group. However, Japanese type 2 diabetes is also changing. In recent years, the data from a 75-g oral glucose tolerance test of 2121 clients showed that insulinogenic index of clients with impaired glucose tolerance was similar to that of a normal glucose tolerance group and that the area under the insulin curve (AUC) was high in younger diabetics. From a life-style modification perspective, the importance of body weight control by diet and exercise as well as refraining from excessive drinking should be emphasized.