A new randomized crossover trial suggests that daily consumption of freeze-dried strawberries may bolster antioxidant defenses, reduce vascular inflammation, and improve fasting glucose in adults with prediabetes.
Background and Rationale
Prediabetes marks a critical transition between normal glucose metabolism and type 2 diabetes (T2DM). It is characterized by mild hyperglycemia that contributes to oxidative stress and inflammation, factors linked to insulin resistance and vascular dysfunction. Polyphenol-rich plant foods, including berries, have shown promise in improving antioxidant capacity and glycemic outcomes, though results vary across studies due to absorption and bioavailability differences.
Study Purpose
Building on prior research indicating anti-inflammatory and antioxidant benefits of strawberries in metabolic disorders, this trial investigated whether daily intake of freeze-dried strawberry powder (FDS) could enhance antioxidant defenses, reduce vascular inflammation, and improve fasting glucose in adults with prediabetes.
Methods
Design and participants
A randomized controlled crossover trial conducted over 28 weeks at the University of Nevada, Las Vegas.
Twenty-five adults meeting the American Diabetes Association criteria for prediabetes participated.
Each participant completed both study phases: 12 weeks of daily FDS intake and 12 weeks of control (no strawberries), separated by a 4-week washout.
Intervention and controls
FDS provided 32 grams per day, equivalent to 2.5 servings of fresh strawberries.
The intake delivered dietary fiber, polyphenols, flavonols, and anthocyanins.
Participants maintained their usual diet and physical activity.
Compliance and measurements
Compliance was assessed via dietary logs, powder returns, and plasma ellagic acid levels.
Measurements occurred at baseline, 12, 16, and 28 weeks.
Primary outcomes included fasting glucose, antioxidant enzymes, total antioxidant capacity, and vascular adhesion molecules.
Carotenoids were analyzed by high-performance liquid chromatography (HPLC).
Statistical analysis
A mixed-model analysis of variance (ANOVA) adjusted for treatment, period, randomization order, age, sex, fasting glucose, and baseline values.
Power analysis indicated adequate sample size to detect meaningful changes in antioxidant and vascular markers.
Key Findings
Antioxidant status
FDS supplementation significantly increased antioxidant biomarkers, including superoxide dismutase (SOD), glutathione (GSH), total antioxidant capacity (TAC), and β-carotene.
No significant changes were observed in catalase, glutathione reductase, glutathione peroxidase, or α-carotene.
Glycemic control
Fasting glucose levels decreased significantly during the FDS period, indicating improved fasting glycemic control.
Vascular inflammation
FDS intake reduced vascular inflammation, evidenced by lower levels of intercellular adhesion molecule (ICAM) and vascular cell adhesion molecule (VCAM).
P-selectin and E-selectin levels did not change.
Correlations
Inverse relationships were observed between ICAM and GSH, TAC, and β-carotene, and between VCAM and TAC, suggesting that better antioxidant status may be linked to reduced vascular inflammation.
Safety and tolerability
Minor adverse effects included mild gastrointestinal discomfort and headaches.
Strengths and limitations
Strengths: randomised crossover design, 12-week phase duration, objective biomarker analyses, and a feasible dietary dose.
Limitations: small sample size with predominantly female participants, lack of a placebo beverage, absence of participant blinding, and single-site recruitment which may affect generalizability.
Conclusions and implications
Twelve weeks of daily FDS intake was associated with improved antioxidant capacity, reduced vascular inflammation, and better fasting glycemic control in adults with prediabetes.
These findings support strawberry consumption as a practical, food-based strategy that may help prevent progression to type 2 diabetes in real-world settings.
Mechanistically, polyphenols may enhance glutathione synthesis and SOD activity, while carotenoids and anthocyanins may mitigate oxidative stress and endothelial dysfunction.
Further research with larger, more diverse populations and longer follow-up is warranted to confirm these effects and clarify long-term clinical benefits.
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