Previous studies have associated the strawberry’s main component, anthocyanin (>75% of its total phenolic compounds), and anthocyanin-rich foods with reductions in cardiovascular disease and diabetes risk. Researchers from the Illinois Institute of Technology and the University of California Davis examined the effects of strawberry consumption at 4 different doses in individuals exhibiting insulin resistance (IR). Twenty-nine obese subjects were enrolled in the study, though just 21 completed it. They exhibited either a fasting blood glucose concentration between 5.5 and 6.9mmol/L, fasting insulin concentration greater than 13.13μIU/mL, or homeostasis model assessment value for insulin resistance (HOMA-IR) ≥1.0.
Study subjects consumed a high-carbohydrate, high-fat meal and 1 of 4 strawberry powder-based beverages: 0g (control), 10g, 20g, or 40g of freeze-dried whole strawberry powder (FDS) where 40g FDS powder was equivalent to approximately 3 cups of fresh strawberries. The authors noted this was the first study to test the effects of FDS in a dose >10g on postprandial metabolism in patients with IR.
Blood levels were measured at 0 minutes and at 30 minute-intervals post-meal until 2 hours, then each hour till 6 hours. Overall, the 40g FDS beverage group displayed significantly reduced post-meal insulin concentrations over 6 hours compared to all other beverages (~12% reduction; P<0.05). Post-meal glucose concentrations, however, did not differ among the beverages though the insulin-to-glucose ratio was significantly different (P<0.05).
The 40g FDS beverage also resulted in the lowest absolute peak insulin concentration (P=0.047) and incremental increase from baseline (P=0.03) postprandially. In addition, oxidized-LDL levels were reduced with 20g FDS consumption (P<0.05) and IL-6 did not differ among the treatment arms.
Some of the study’s limitations included the lack of FDS placebo powder, the lack of other non-anthocyanin plasma data, additional inflammatory marker assessment, and the fiber controlled aspect that may have minimized observing the larger effect on glucose variables. Despite these limitations, the authors assert the importance as an initial step in devising dietary recommendations for a growing population of individuals with metabolic disorders rooted in obesity and insulin resistance. Study findings generally support a role for strawberries in improving insulin sensitivity in patients with insulin resistance.
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