Can Two Tablespoons of Olive Oil a Day Treat Depression?

Depression is the leading cause of disability worldwide. Over 280 million people suffer from it globally, and the numbers have surged since 2020. Despite decades of research, roughly one-third of patients don't respond adequately to standard antidepressant medications — a phenomenon psychiatrists call "treatment-resistant depression."

This treatment gap has driven intense interest in complementary approaches — dietary interventions, exercise, mindfulness, and increasingly, specific food compounds. Among these, one substance has quietly accumulated a striking body of evidence: extra virgin olive oil.

The connection isn't new. Epidemiological studies have long noted that populations eating traditional Mediterranean diets — where olive oil is consumed by the cupful, not the teaspoonful — have substantially lower rates of depression and anxiety. But correlation isn't causation. Is it the olive oil itself, or the sunshine, social eating, and slower pace of life?

In 2022, a research team from Shiraz University of Medical Sciences in Iran designed one of the most rigorous experiments to date to answer that question. Their answer was unambiguous — and it challenges assumptions about what "treating" depression can look like.

The study enrolled 73 patients with clinically diagnosed major depressive disorder (MDD) in Shiraz, Iran. This wasn't a study on "feeling a bit down" — participants had been formally diagnosed using DSM criteria, the gold standard in psychiatric diagnosis.

Patients were randomly assigned to two groups:

The choice of sunflower oil as the control is methodologically important. Both oils are liquid fats with similar caloric content (~200 kcal per 25 mL). The critical difference: sunflower oil is almost devoid of polyphenols. If the EVOO group improved and the sunflower group didn't, the effect could be attributed to olive oil's bioactive compounds — not just the act of consuming dietary fat.

The study was double-blind — neither the patients nor the researchers knew which oil was being consumed until the data was analyzed. Both oils were packaged in identical opaque containers. Depression was measured using two validated instruments:

• Beck Depression Inventory-II (BDI-II) — a 21-item self-report questionnaire, considered the gold standard for measuring depression severity
• 7-item Hamilton Depression Rating Scale (HAMD-7) — a clinician-rated scale that assesses depressed mood, guilt, suicidal ideation, work and interests, psychic anxiety, somatic symptoms, and general symptoms

The researchers also measured serum brain-derived neurotrophic factor (BDNF), salivary cortisol levels at awakening and 30 minutes post-awakening, and cortisol awakening response — attempting to understand not just whether olive oil helps depression, but how.

The headline finding was clear: EVOO significantly reduced depression symptoms compared to sunflower oil. But the details reveal a more nuanced — and in some ways more interesting — story.

The idea that a dietary fat could influence psychiatric symptoms sounds implausible until you understand the emerging science of neuroinflammation — the concept that chronic, low-grade inflammation in the brain plays a central role in depression.

The Foshati study doesn't exist in a vacuum. It builds on — and substantially strengthens — a growing body of evidence:

No study is perfect, and intellectual honesty requires examining the caveats:

Not yet — but it's an important brick in an increasingly compelling wall.

Here's why we find this study particularly significant:

The study design is strong. Double-blind, randomized, intention-to-treat analysis, validated outcome measures, clinician-rated and self-reported scales. This isn't a flimsy survey study or an in-vitro experiment. It's a properly designed clinical trial that would pass peer review at any major journal — and it did, appearing in the Journal of the Academy of Nutrition and Dietetics, a top-tier nutrition journal.

The severity finding is biologically coherent. The fact that EVOO worked in severe depression but not mild/moderate isn't a weakness — it's actually what you'd predict if the mechanism is anti-inflammatory. Severe depression involves more neuroinflammation. More inflammation means more target for polyphenols to act on. This isn't a ceiling effect; it's a dose-response relationship between disease severity and treatment response.

The effect size matters. A P-value of .008 on the HAMD-7 for severe depression is robust. In a field where many antidepressant trials barely scrape statistical significance with hundreds of patients, achieving P = .008 with a food intervention in 73 patients is noteworthy.

The risk-benefit ratio is unbeatable. Even if the effect is modest, the "side effects" of 25 mL of EVOO per day include improved cardiovascular health, reduced cancer risk, better cognitive function, and lower systemic inflammation. No pharmaceutical can make that claim. The worst-case scenario of trying this intervention is that you consumed a healthy fat.