Blueberries are rich in flavonoids, a type of antioxidant compound, and in-particular the antioxidants known as anthocyanins and flavanols. William T. Cefalu, from Louisiana State University (Louisiana, USA), and colleagues enrolled 32 obese, non-diabetic, and insulin-resistant men and women, average age of 51.5 years and an average BMI of 37.4 kg/m2, in a six-week long study.,  Subjects either received a smoothie containing 22.5 grams of blueberry bioactives or a placebo blend equal nutritional value.  Subjects consumed two smoothies daily for six weeks.  At the end of the study, the team found that 67% of subjects who consumed the blueberry smoothie experienced at least a 10% or greater favorable change in insulin sensitivity.  The researchers propose that: “Daily dietary supplementation with bioactives from whole blueberries improved insulin sensitivity in obese, nondiabetic, and insulin-resistant participants.”