Strawberries May Support Glucose Control and Reduce Inflammation in Prediabetes, Study Finds
Key Takeaways:
- Daily intake of freeze-dried strawberries for 12 weeks improved fasting glucose and reduced inflammation in adults with prediabetes.
- Antioxidant biomarkers including superoxide dismutase, glutathione, and β-carotene significantly increased during strawberry supplementation.
- Findings suggest strawberries could serve as a practical, food-based intervention to prevent progression to type 2 diabetes.
Strawberries and prediabetes: A promising link
A new randomised controlled trial published in Antioxidants has found that consuming freeze-dried strawberries (FDS) daily may help reduce fasting blood glucose and vascular inflammation in adults with prediabetes. The research also showed marked improvements in antioxidant status, highlighting the potential of strawberries as a simple dietary intervention for metabolic health.
The authors concluded that “strawberries may represent a practical dietary intervention that improves fasting glucose and strengthens antioxidant defence in adults with prediabetes.”
Understanding prediabetes and oxidative stress
Prediabetes represents a critical stage between normal glucose metabolism and type 2 diabetes mellitus (T2DM). It is characterised by mildly elevated blood glucose levels, which contribute to oxidative stress and low-grade inflammation.
High glucose levels increase reactive oxygen species (ROS), impairing insulin function and damaging pancreatic β-cells. Proinflammatory cytokines such as tumour necrosis factor-alpha (TNF-α) further aggravate insulin resistance by interfering with glucose uptake and triggering inflammatory pathways. Over time, these effects contribute to vascular dysfunction and atherosclerosis through increased endothelial adhesion molecules and reduced antioxidant enzyme activity.
Dietary antioxidants – including vitamins, polyphenols, and carotenoids – can neutralise oxidative stress. However, studies using supplements have produced inconsistent results due to differences in absorption and bioavailability. Evidence from clinical trials and meta-analyses indicates that plant-based antioxidants can improve total antioxidant capacity and glycaemic outcomes in people with prediabetes or T2DM.
Berries, particularly strawberries, are rich in polyphenols such as anthocyanins and ellagic acid, which are known to enhance antioxidant enzyme activity and improve insulin sensitivity. Previous studies using FDS have already shown benefits for inflammation and oxidative stress in metabolic disorders, providing a foundation for this new research.
Study design and methodology
Researchers at the University of Nevada, Las Vegas, conducted a 28-week randomised controlled crossover trial involving 25 adults who met the American Diabetes Association’s diagnostic criteria for prediabetes.
Each participant completed two 12-week phases: one with daily FDS intake and another control period without strawberries, separated by a four-week washout. Participants were randomly assigned to begin with either the FDS or control phase.
During the intervention, participants consumed 32 grams of FDS powder per day – equivalent to roughly 2.5 servings of fresh strawberries – containing dietary fibre, polyphenols, flavonols, and anthocyanins. They were instructed to maintain their usual diet and physical activity throughout the trial.
Compliance was carefully monitored using dietary logs, returned powder packets, and plasma ellagic acid levels. Blood samples were collected at baseline, 12, 16, and 28 weeks to measure fasting glucose, antioxidant enzyme activity, total antioxidant capacity, and vascular adhesion molecules using standardised assays. Carotenoid levels were analysed via high-performance liquid chromatography (HPLC).
A mixed-model analysis of variance (ANOVA) was used to evaluate treatment effects while accounting for treatment period, randomisation order, age, sex, fasting glucose, and baseline values. Power analysis confirmed the study was adequately powered to detect meaningful changes in metabolic and antioxidant markers.
Improvements in antioxidant and metabolic markers
Results showed high adherence rates, with more than 85% compliance confirmed by elevated plasma ellagic acid during the FDS phase.
Compared with the control period, strawberry supplementation produced significant improvements in several antioxidant biomarkers, including superoxide dismutase, glutathione (GSH), total antioxidant capacity (AC), and β-carotene. No significant changes were observed in catalase, glutathione reductase, glutathione peroxidase, or α-carotene.
Fasting blood glucose levels also decreased significantly during the FDS period, indicating better glycaemic control. Moreover, markers of vascular inflammation – particularly intercellular adhesion molecule (ICAM) and vascular cell adhesion molecule (VCAM) – were notably reduced. Levels of P-selectin and E-selectin remained unchanged.
Correlation analyses revealed modest inverse relationships between ICAM and GSH, AC, and β-carotene, and between VCAM and AC, suggesting that stronger antioxidant status was associated with reduced vascular inflammation.
Only minor side effects were reported, such as mild gastrointestinal discomfort and headaches.
Implications and limitations
The findings suggest that incorporating strawberries into the diet could help strengthen antioxidant defences, lower inflammation, and improve fasting glucose regulation in people with prediabetes. These benefits may be linked to polyphenols enhancing glutathione synthesis and superoxide dismutase activity, alongside carotenoids and anthocyanins reducing oxidative stress and endothelial dysfunction.
The study’s strengths include its randomised crossover design, objective biomarker measurements, and the use of a realistic dietary dose of strawberries. However, the relatively small and predominantly female sample, the absence of a placebo control drink, lack of participant blinding, and single-site recruitment limit the generalisability of results.
The study was funded by the California Strawberry Commission.
A food-based approach to diabetes prevention
In summary, consuming a daily portion of freeze-dried strawberries for 12 weeks led to measurable improvements in antioxidant capacity, fasting glucose, and vascular inflammation among adults with prediabetes.
While further research in larger, more diverse populations is needed, these results point to strawberries as a simple, accessible dietary strategy that could help prevent the progression from prediabetes to type 2 diabetes in everyday clinical and public health settings.
CCH insights
It is great to have research that shows health benefits from eating strawberries, because nearly everyone loves strawberries and there aren’t many foods that are extremely popular and good for us. However, the amount of freeze-dried strawberries consumed in this study would set you back about £20 per week – not a huge amount, but during a cost-of-living crisis might not be feasible for many people. This study was, unsurprisingly, funded by the California Strawberry Commission, and it begs the question whether eating other berries or certain other foods might not have a similar effect – but credit to the strawberry industry for making the effort to do the research.
