Energy-adjusted Dietary Inflammatory Index mediates the association between obesity and depressive symptoms: a population-based analysis of the National Health and Nutrition Examination Survey 2007–2018

Epidemiological and clinical research has confirmed a link between obesity and depressive symptoms, with inflammation as a potential common mechanism. Given that dietary components modulate inflammation and relate to both conditions, investigating dietary inflammation as a potential underlying pathway is necessary. Herein, we aimed to explore the potential role of the Energy-adjusted Dietary Inflammatory Index (E-DII) in explaining the relationship between obesity and depressive symptoms. We conducted a cross-sectional analysis of the 2007-2018 National Health and Nutrition Examination Survey cohort, enrolling 20 324 participants. Obesity and dietary inflammation were assessed by BMI and E-DII, respectively. Depressive symptoms were evaluated using the nine-item Patient Health Questionnaire-9. We found that obesity and inflammatory diets were positively associated with depressive symptoms (<i>β</i> = 0·50, 95 % CI 0·30, 0·69; <i>β</i> = 0·35, 95 % CI 0·19, 0·50; both <i>P</i> < 0·001), and variations in the association among obesity, pro-inflammatory diets and depressive symptoms were evident across various population subgroups (e.g. sex, age, chronic diseases and smoking status subgroups, <i>P</i>_{for interaction} < 0·050). After adjusting for all covariates, E-DII accounted for 4 % of the obesity-depression association. Despite this modest proportion, the finding identifies dietary-induced inflammation as a statistically significant, modifiable pathway. In conclusion, obesity and pro-inflammatory diets are linked to an increased risk of depressive symptoms, with E-DII serving as a modest but significant modifiable pathway. These findings highlight dietary intervention as a potential strategy for mitigating depressive symptoms in individuals with obesity.