Harnessing Dietary Tryptophan: Bridging the Gap Between Neurobiology and Psychiatry in Depression Management.

Major depressive disorder remains a leading cause of disability worldwide, with conventional antidepressants offering incomplete and often transient relief. Mounting evidence highlights disturbances in tryptophan (Trp) metabolism as a key biological axis linking inflammation, neuroplasticity, and mood regulation. Plant-derived compounds that modulate this pathway, including 5-hydroxytryptophan, isoflavones, berberine, and polyphenols, have emerged as promising candidates for integrative treatment strategies. Yet, despite encouraging preclinical and clinical findings, knowledge gaps persist regarding long-term efficacy, mechanistic specificity, and standardized therapeutic protocols. This narrative review explores how Trp modulators influence central and peripheral mechanisms relevant to depression, from serotonergic synthesis and kynurenine shunting to gut-brain-immune interactions. Evidence from animal models and randomized clinical trials is critically synthesized, with particular attention to outcomes on mood stabilization, anxiety reduction, cognitive function, and sleep regulation. Special emphasis is placed on translational potential, methodological limitations, and the need for harmonized research frameworks. Here we highlight that phytochemical interventions represent a mechanistically informed and biocompatible strategy for advancing depression management. By bridging neurobiology and clinical psychiatry, these insights may pave the way for next-generation therapeutics that integrate dietary, microbiota-targeted, and anti-inflammatory approaches. Broader application of this research could ultimately refine personalized psychiatry, expand therapeutic horizons, and contribute to global mental health resilience.