Walnut consumption improves mood and is associated with increased urinary excretion of 5-hydroxyindoleacetic acid and urolithins in a randomized crossover trial

Background & aims: Walnuts are nutrient-dense foods rich in bioactive compounds that may support mental health. However, evidence linking walnut consumption to mood regulation and to changes in urinary metabolites potentially associated with these effects in humans remains limited. This randomized crossover trial (RCT) aimed to evaluate the effects of an 8-week walnut (Juglans regia) intervention on mood states in young adults and to explore the potential mechanistic links through urinary serotonin metabolite (5-hydroxyindoleacetic acid, 5-HIAA), cortisol, and urolithins.