Do inflammation and adiposity mediate the association of diet quality with depression and anxiety in young adults?

Background & aims: 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. Methods: We used data of 3331 participants from the 1993 Pelotas Birth Cohort (Brazil). Data on dietary intake and inflammatory markers were assessed at 18 years, and information on mental disorders was obtained at both 18 and 22 years. A food frequency questionnaire was used to assess dietary intake, and diet quality was estimated using the Brazilian Healthy Eating Index - Revised (BHEI-R). The occurrence of MDD and GAD was assessed using the Mini International Neuropsychiatric Interview (MINI), conducted by psychologists. The associations of diet quality, BMI and inflammatory markers with mental disorders were explored using logistic regression. The mediation analysis was performed using structural equation modelling. Results: A one standard deviation increase in the diet quality score at age 18 years was associated with both lower levels of CRP (-0.06 mg/L; 95% CI: -0.10; -0.008) at 18 years and 23% lower odds of MDD at 22 years (OR: 0.77; 95% CI: 0.61; 0.97). No association was found between diet quality score and both BMI and GAD. Obesity was associated with higher odds of MDD, but CRP and IL-6 were not associated with MDD or GAD. Our results provide no evidence that inflammatory markers and BMI mediate the association between diet quality and MDD in young adults. Conclusions: A better diet quality is associated with lower occurrence of MDD among young adults, but we did not find evidence that inflammatory markers and BMI mediate this association. (c) 2021 Elsevier Ltd and European Society for Clinical Nutrition and Metabolism. All rights reserved.