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Abstract

Background: Many patients with depression are reluctant to take psychiatric medications. Hence, complementary therapies such as nutritional considerations could be advantageous. The antidepressant potential of olive oil has been proved in observational studies.

Objective: The effect of extra-virgin olive oil (EVOO) on depression symptoms and cortisol and brain-derived neurotrophic factor (BDNF) levels in patients with depression was examined.

Design and participants: This was a double-blind randomized controlled trial conducted on 73 patients suffering from major depressive disorder in Shiraz, Iran, in 2016.

Intervention: The patients were randomly assigned to intervention (EVOO) and control (sunflower oil) groups and consumed 25 ml/day of the corresponding oil for 52 days.

Main outcome measures: Depression symptoms were assessed by Beck Depression Inventory-II (BDI-II) and 7-item Hamilton Depression Rating Scale (HAMD-7). Salivary cortisol levels were determined immediately after awakening (T₀) and 30 minutes later (T₃₀). Cortisol awakening response (CAR) and the area under the curve with respect to ground (AUC_G) and increase (AUC_I) were computed. Serum BDNF concentrations were also measured.

Statistical analyses performed: Statistical analysis was conducted based on intention-to-treat (ITT) and per-protocol (PP) approaches. Within-group changes were examined with repeated measures (for BDI-II and HAMD-7) and with paired t-test (for other variables). Between-group comparisons were performed with analysis of covariance after adjustment for confounding factors.

Results: In ITT analysis, HAMD-7 score was the only variable with significant changes within and between groups, the latter as a greater decline in EVOO group (P=0.001). BDI-II score did not show significant change in either group but the between-group comparison revealed a significant difference (P=0.021). EVOO showed antidepressant effect in severely depressed patients (P=0.017 for BDI-II and 0.008 for HAMD-7) but not in mild/moderate depression category. Serum BDNF concentrations, salivary cortisol levels at T₀ and T₃₀, CAR, AUC_G, and AUC_I did not change within or between groups. Results of PP analysis were not different.

Conclusions: The results of this study suggested beneficial effects of EVOO on depression symptoms in patients with severe depression but not in those with mild to moderate depression. The effects were significant from both statistical and clinical points of view.

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