Physical Activity as a Mediator of the Relationship Between Mediterranean Diet Adherence and Anxiety Symptoms in Chilean Adolescents: A Cross-Sectional Study

Background: Adolescent mental health is a global concern, with lifestyle factors such as diet and physical activity (PA) playing a crucial role. While the Mediterranean Diet adherence (MDA) is known for its neuroprotective benefits on mental health, the mechanisms by which they are related remain unclear. Therefore, the aim of this study was twofold: (1) to examine the associations between MDA, PA, and screen time (ST) with anxiety symptoms, depression, stress, and total psychological distress in Chilean adolescents; and (2) to determine whether PA mediates the relationship between MDA and anxiety symptoms. Methods: A cross-sectional study was conducted with 322 Chilean school-aged adolescents 158 males and 164 females (14.98 ± 1.96 years). Mental health outcomes (depression, anxiety, and stress) and lifestyle behaviors, including MDA, PA, and ST, were comprehensively assessed using validated self-reported questionnaires. Results: After adjusting for age and sex, multiple linear regression models showed that higher MDA was significantly and inversely associated with anxiety (b = −0.23, p = 0.044), stress (b = −0.25, p = 0.022), and total psychological distress (b = −0.72, p = 0.022). Conversely, ST was identified as a consistent risk factor, positively predicting higher levels of anxiety (b = 0.45, p = 0.008), stress (b = 0.42, p = 0.008), and total distress (b = 1.11, p = 0.014). Furthermore, PA was inversely linked to anxiety (b = −0.35, p = 0.013) and successfully mediated the relationship between MDA and anxiety symptoms (Indirect Effect = −0.047, 95% CI: −0.10 to −0.01). No significant mediation effects were observed for depression or stress. Conclusions: The present study identifies robust inverse associations between MDA and symptoms of anxiety, depression, and stress in Chilean adolescents. A key finding is the specific pattern of relationships observed: while higher MDA is directly linked to lower levels of depression and stress, its association with anxiety is shared with levels of PA. Despite these findings, the cross-sectional nature of the study limits the establishment of causal relationships, and further longitudinal research is needed to confirm these directional pathways.