Among them, several tryptophan metabolism-related metabolites such as tryptophan, kynurenine, serotonin, and indole derivatives, which were slightly increased in the gardening groups compared to in the control, showed a positive correlation with growth factor levels and cortisol (BDNF, VEGF, and PDGF) and psychological factors (life satisfaction and cognitive ability), while loneliness and depression were negatively correlated. The gene discussed is BDNF; the disease is major depressive disorder.