Effects of different levels of dietary protein on controlling diabetes and oxidative stress status in rats

ABSTRACT

The present study was conducted to evaluate the effect of dietary protein at different levels on controlling diabetes and antioxidant stress status in rats. Thirty-five male rats [average weight 181.6 + 5.8 g] were used in this study. Rats were divided into five groups [7 rats each]; group 1 received basal diet until the end of the study while the other rats were made diabetic by Streptozotocin injection and assigned to four groups group 2 [diabetic control] fed a basal diet, whereas groups [3], [4] and [5] fed diets containing different levels of protein [5, 20 and 30% of energy respectively]. Initial blood glucose and insulin levels were determined on day 1. Initial weight and once weekly and daily food intakes [FI] were .recorded. After 4 weeks [wk], rats were sacrificed and.blood was collected and analyzed for various biochemical parameters. Diabetic rats on the high-protein diet [30%] had average daily FI and percentage change in body weight [Wt] significantly higher [p<0.05] than that of the diabetic control [10.55 g; 14.77% vs. 8.33 g; -17.89%]. T. ptn and Alb levels in diabetic rats fed the high-protein diet significantly increased [6.766; 4.453 vs. 5.726; 3.503 g/dL for diabetic control]. Glucose and insulin levels significantly improved [190.286 mg/dL; 17.41 mU/L vs. 236.754 and 11.96 for diabetic control]. The high-protein diet did not alter Crn and BUN levels, indicating unaffected kidney functions [0.937 mg/dL; 16.81 mmol/dL vs. 1.113; 20.401 mmol/dL for diabetic control]. Lipid profiles of diabetic rats on high-protein significantly improved. Serum levels of T.chol, TGs, HDLc and LDL-c were 180; 90.714; 55.572 and 106.286 respectively vs. 208.571; 111.713; 44.57 and 141.657 mg/dL for diabetic control. Oxidative stress induced by diabetes was favorably altered due to increased protein intake. Blood levels of GSH, TBARs and vitamin E in the high-protein fed rats were 51.433 mg%; 0.513 nmol/ml and 17.803 mg/dL vs. 41.301mg%; 0.771 nmol/ml and 12.161 mg/dL for the diabetic control. Considering all the tested parameters, the 20% protein diet was not as effective as the 30% in achieving these favorable alterations, while the 5% protein diet worsened the diabetic state as well as the oxidative status in diabetic rats. Results of this study indicated that increasing dietary protein up to 30% of energy intake in diabetic rats maintained and improved Wt, improved fasting blood glucose, insulin and lipid profiles without adverse effects on kidney functions. In addition, it improved oxidative status in diabetic rats. Long-term dietary studies are necessary to ensure the safety of high protein on controlling diabetes