Pharmacokinetic Evaluation of Red Raspberry (Poly)phenols from Two Doses and Association with Metabolic Indices in Adults with Prediabetes and Insulin Resistance

This study aimed to investigate pharmacokinetic variables of two doses of red raspberry (RR) (poly)phenols and their association with metabolic indices in adults with prediabetes and insulin resistance (preDM-IR) compared to metabolically healthy adults (reference). Thirty-two adults (preDM-IR, n = 21; reference, n = 11) consumed three meals containing 0 g (control), 125 g, or 250 g of frozen RR on three separate days in random order. Plasma (poly)phenolic metabolites and metabolic indices were characterized over a 0–8 h period and again at 24 h. Twenty-four metabolites were significantly increased by RR interventions in all subjects (p < 0.05). Individuals with preDM-IR compared to reference had a lower capacity to generate several metabolites, including 4′-hydroxy-3′-methoxycinnamic acid and hydroxymethoxycinnamic acid isomer, both negatively correlated with postprandial insulin concentrations (p < 0.05). The results suggest that RR (poly)phenols are metabolized in a dose-related manner, and further research is required to understand their role in insulin management.