Objective To observe the changes of body composition, metabolic profile, and morphology and secretary status of islet β/α cells with high-fat diet (HFD, calorie is 5.86 kcal/kg) and calorie restrict diet (CRD, calorie is 1.6 kcal/kg) from middle adulthood to later adulthood. Methods A total of 45 male SD rats, 14 to 16 months of age were randomly divided into normal diet (ND), HFD and CRD groups. At 0(14?16 months), 8(16?18 months), 16(18?20 months) weeks, body weight (BW), visceral fat, body fat ratio were measured as body composition; blood was collected to detect triglyceride and cholesterol as lipid profile, as well as free fatty acid (FFA), fasting blood glucose and insulin. HOMA-IR, HOMA-β and ISI were calculated according to the levels of fasting glucose and insulin. The secretary status of insulin and glucagon in islet were assessed by immunohistochemistry, and the area of α/β-cell was measured. Results In adult rats, BW, visceral fat, body fat ratio, lipid profile, FFA, fasting glucose and insulin were increased with aging, meanwhile HOMA-IR increased while HOMA-β and ISI were decreased (P＞0.05), and the areas and levels of insulin and glucagon within islet had no significant change. In HFD group, BW, visceral fat, body fat ratio, triglyceride, FFA, fasting glucose and insulin were significantly increased during the 16 weeks, HOMA-IR was increased while ISI decreased, and levels of insulin and glucagon within islet were dramatically increased(P＜0.05). In CRD group, BW, visceral fat, body fat ratio, triglyceride, FFA, fasting glucose, insulin and HOMA-IR were all decreased, while HOMA-β and ISI were increased, and levels of insulin and glucagon within islet were dramatically decreased(P＜0.05). Conclusion The age-related changes of increased insulin resistance, decreased insulin sensitivity were deteriorated by HFD, and improved by CRD. FFA was the earliest and most common impact factor in both HFD and CRD. As insulin levels in both serum and islet were increased in HFD group at 8 weeks, islet glucagon levels was decreased significantly at the same time in CRD group, β cell was the targeted cells by HFD whereas α cells by CRD.