The impact of almond supplementation on oxidative stress biomarkers: a systematic review and meta-analysis of randomized control trials.

Oxidative stress, an imbalance between reactive oxygen species and antioxidants, contributes to chronic diseases. Almonds, rich in vitamin E, polyphenols, and monounsaturated fats, exhibit antioxidant potential, though their overall effects on oxidative biomarkers are unclear. This systematic review and meta-analysis evaluate almond supplementation's impact on these biomarkers in adults. Following PRISMA guidelines, PubMed, Scopus, and Web of Science were searched up to January 2025. Randomised controlled trials (RCTs) and crossover trials assessing biomarkers of antioxidant and oxidation status (e.g., malondialdehyde [MDA], superoxide dismutase [SOD], glutathione peroxidase [GPx], 8-hydroxy-2'-deoxyguanosine [8-OHdG], uric acid [UA]) were included. Risk of bias was evaluated using the Cochrane Tool, and random-effects models calculated weighted mean differences (WMDs) with 95% confidence intervals (CIs). Eight studies (5 RCTs, 3 crossover trials; n = 424) were included. Almond doses of > 60 g/day significantly reduced MDA (WMD = -0.46, p = 0.002), 8-OHdG (WMD = -5.83, p < 0.001), and UA (WMD = -0.64, p = 0.009), while increasing SOD (WMD = 2.02, p = 0.008). No effect was found for GPx (p = 0.270). High heterogeneity (I² = 92-96%) indicated variability in study design, dosage, and population. Almond supplementation (> 60 g/day) significantly improves oxidation status by reducing MDA, 8-OHdG, and UA while enhancing SOD activity. These findings support almonds as a functional food for oxidation management. However, high heterogeneity underscores the need for standardized trials to confirm optimal dosage, duration, and conditions. Trial registration: Prospero-CRD42025646264.