Blueberry diets improve glucose tolerance and decrease oxidative stress in spontaneously hypertensive stroke‐prone rats

Abstract

Metabolic syndrome, characterized by insulin resistance, hyperglycemia and dyslipidemia, is a risk factor for cardiovascular disease. Eating fruits and vegetables benefits the symptoms of metabolic syndrome, and so we tested the effects of blueberries on insulin resistance in spontaneously hypertensive stroke‐prone rats (SHRSP). Control rats (WISTAR) and SHRSP were fed either a control AIN93G diet (CON) or a diet containing 1% or 3% freeze‐dried blueberry extract (BB) for 6 wks. All rats drank 2% NaCl. Plasma glucose and insulin were measured prior to and 15, 30, and 60 min following oral gavage of 40% glucose. The overall insulin response (AUC) to oral glucose was lower in SHRSP compared to WISTAR on CON diet (p<0.05), resulting in glucose being elevated in SHRSP at 15 minutes (p<0.001). In contrast, SHRSP fed 1% and 3% BB had insulin responses similar to WISTAR and there were no significant differences in plasma glucose levels between the groups. SHRSP showed signs of oxidative stress, with elevated levels of F2‐isoprostanes/creatinine in the urine (p<0.05). Feeding 3% BB lowered F2‐isoprostanes to normal values. There was no evidence of dyslipidemia in SHRSP. Our data suggest that SHRSP fed BB have less oxidative stress, and improved overall health. As well, feeding blueberries made animals better able to withstand a glucose challenge by increasing the insulin response, thereby decreasing blood glucose levels. Including blueberries in the diet may benefit metabolic syndrome. Funded by NSERC & Atlantic Innovation Fund.