Diet quality has been inversely associated with depression, but less is known about its association with anxiety and about the mechanisms involved in the association between diet and mental health. This study aimed to assess the associations of diet quality with major depressive disorder (MDD) and generalized anxiety disorder (GAD) in young adults, and to explore whether inflammation, indexed by interleukin-6 (IL-6) and C-reactive protein (CRP), and body mass index (BMI) mediate this association.