Abstract: Objective: To investigate the effects of long-term protein diet with normal total calorie intake on glucose-stimulated insulin secretion in normal rats. Methods: 51 healthy male Wistar rats (8 weeks old) were selected and divided into three groups: the routine feed group (NC, n=16), the high protein diet group (HP, n=19) and the low protein diet group (LP, n=16). The total calorie ingestion of each rat per day was similar and was used for 24 weeks. Body weight, fasting blood glucose (FBG) and fasting plasma insulin (FINS) were monitored during feedings. The insulin secretary function of β cells, especially the acute insulin response(AIR) were determined by the intravenous glucose tolerance test (IVGTT) in 32-week-old rats. Results: 1. Body weight and visceral fat mass: Compared with the NC group, there were no differences of the HP or LP groups. 2. IVGTT: (1) Blood glucose: There were no differences among the three groups. (2) Plasma insulin: 5min- and 10min- plasma insulin levels were markedly higher in the HP group than in the NC group［(6.5±0.8)ng/ml vs (4.9±0.7)ng/ml, P＜0.001; (3.9±0.6)ng/ml vs (3.1±0.5)ng/ml, P＜0.001］, and there were no differences between the LP and NC groups. Conclusion: The long-term high protein ingestion with total calorie may significantly enhance the AIR by IVGTT in rats, while low protein intakes has not significant effect on insulin secretion in rats.

Key words: Dietary protein, Blood glucose, Insulin, Islet cell function