Effects of dietary onion (Allium cepa L.) in a high-fat diet streptozotocin-induced diabetes rodent model

Background/Aims: The present study was conducted to investigate the effects of two dietary doses of freeze-dried onion powder on diabetes-related symptoms in a high-fat (HF) diet streptozotocin (STZ)-induced diabetes rat model. Methods: Five-week-old male Sprague-Dawley rats were fed a HF diet for 2 weeks and then randomly divided into 4 groups as follows: HF control (HFC), diabetic control (DBC), onion low (ONL; 0.5%) and onion high (ONH; 2.0%). Diabetes was induced by an intraperitoneal injection of STZ (40 mg/kg body weight) in all groups except the HFC group. Results: After 4 weeks on the experimental diets, fasting blood glucose levels for both onion-fed groups were higher than in the DBC and HFC groups, albeit only significantly so (p < 0.05) in the ONL group. Serum insulin concentrations and insulin resistance were dose-dependently increased (however, not significantly so) in the onion-fed groups compared to the DBC group. Pancreatic beta-cell function and liver glycogen concentrations were nonsignificantly higher in the DBC and ONH groups compared to the ONL group. Additionally, the ONH group had significantly higher lipid concentrations (except for high-density lipoprotein cholesterol) compared to all other groups. The ONL group showed a similar hyperlipidemic trend, however to a lesser extent, with only triglycerides significantly differing from those of the DBC and HFC groups. Conclusion: The results suggest that the HF onion diet may increase insulin secretion and consequently insulin resistance in a dose-dependent manner, resulting in a worsened hyperglycemic and hyperlipidemic diabetic state. We conclude that higher dietary fat may impair the antidiabetic effects of dietary onion intake as has been previously reported. Copyright (c) 2008 S. Karger AG, Basel.