Biomarkers of Depressive Disorder and Dietary Intervention Strategies

Depressive disorder (DD) is a multifactorial mental illness involving dysregulation across neuroendocrine, immune, metabolic, and microbial systems. Despite substantial research progress, diagnostic and therapeutic approaches remain largely symptom-based, lacking biological precision. This study addresses this gap by systematically reviewing key biomarkers, such as cortisol, IL-6, CRP, BDNF, and the kynurenine/tryptophan ratio, and examining their modulation through dietary interventions. Using an integrative literature analysis spanning psychiatry, molecular biology, and nutritional science, the paper explores how the Mediterranean diet, anti-inflammatory diet, and probiotics/prebiotics regulate inflammatory cytokines, neurotrophic factors, and gut microbiota activity. Results indicate that these nutritional models can attenuate systemic inflammation, enhance neurotrophic signaling, normalize HPA axis function, and restore microbial balance, thereby improving depressive symptoms. The findings underscore the potential of a biomarker-guided, diet-based framework for precision management of depression. Academically, the study contributes to the conceptual integration of biomarker and nutritional psychiatry research; practically, it offers an evidence-based foundation for individualized, non-pharmacological adjunct therapies in mental health care.