A randomised, double-blind, placebo-controlled trial to assess the postprandial dose-dependent effects of wild blueberries on metabolic and cognitive outcomes following a high-carbohydrate breakfast

Abstract Purpose Despite equivocal human study data, anthocyanin-rich blueberries are associated with positive glycaemic effects which could benefit satiety and other cardiometabolic outcomes. The objective of this study was to examine the dose-dependent effects of freeze-dried wild blueberries on postprandial glucose response simultaneously with changes in satiety, blood pressure and cognitive function. Methods Twenty-four healthy participants (F = 22), mean BMI 22.9 kg/m 2 and mean age 28 years were recruited to a randomized crossover study in which they received a carbohydrate-rich breakfast with a wild blueberry or placebo-matched drink (250 mL) providing 0, 150, 300 or 450 mg anthocyanins. At baseline and at 30 min intervals during the 3-h postprandial phase, blood pressure, subjective appetite ratings and gastrointestinal satiety hormones from a plasma sample (up to 150 min) were recorded. Blood glucose was measured using continuous glucose monitoring. Cognitive performance was assessed at baseline and 90 min post-meal consumption. Results Postprandial glucose and insulin levels declined in a dose-dependent manner. Medium and high doses showed significantly lower glucose and insulin compared to control during the first hour. Concurrently, satiety hormones GLP-1, PYY, and GIP demonstrated significant increases, most pronounced at the highest dose (450 mg anthocyanins), although subjective appetite was unaltered. Cognitive assessments using the Visual Verbal Learning Test, Corsi test and Rapid Visual Information Processing test revealed no significant intervention effects and blood pressure was unaffected. Conclusion Wild blueberry effects on postprandial glucose and appetite hormone responses were evident at anthocyanin doses of 300 mg and above but did not impact other outcomes in healthy adults. Further studies should include individuals with metabolic and/or cognitive vulnerability in longer term interventions to confirm benefits of wild blueberries.