Evidence Explorer · MS-N219 · Nutrition and dietary patterns · Appraised November 3, 2026

A Mediterranean eating pattern supplemented with extra-virgin olive oil produced a large breast-cancer incidence signal in a randomized cardiovascular-prevention trial—but the cancer analysis was secondary, based on only 35 cases, and later required correction for protocol deviations in the parent trial.

What was studied

PREDIMED randomized 4,282 women aged 60–80 years at high cardiovascular risk to Mediterranean diet plus extra-virgin olive oil, Mediterranean diet plus nuts, or advice to reduce dietary fat. The prespecified breast-cancer analysis included 4,152 women without prior breast cancer and a median 4.8 years of follow-up.

Thirty-five invasive breast cancers were confirmed. Rates were 1.1, 1.8 and 2.9 per 1,000 person-years, respectively. Versus control, adjusted hazard ratios were 0.32 (95% CI 0.13–0.79) for the olive-oil group and 0.59 (0.26–1.35) for the nut group.

What this evidence cannot establish

Breast cancer was a secondary outcome and the estimate rests on very few events. The population was older and selected for cardiovascular risk, limiting generalizability.

The PREDIMED parent trial had protocol deviations at some centers; derivative analyses were corrected and reanalyzed. This record therefore treats the result as hypothesis-strengthening, not proof that olive oil prevents breast cancer.

Practical safety context

This was a whole-diet program, not an olive-oil supplement trial. It does not justify replacing screening, risk-reducing medication or indicated surgery.

Nuts can cause severe allergy, and added fats can be difficult during nausea, pancreatic insufficiency or other treatment-related gastrointestinal problems.

Questions for the care team

• Does this eating pattern fit my energy, protein and symptom needs?
• Am I at elevated breast-cancer risk that warrants established risk-reduction options?
• If I have diabetes, weight loss or digestive symptoms, how should the pattern be adapted?

Sources

• PREDIMED breast-cancer randomized secondary analysis (PMID 26365989)
• Published correction on protocol deviations and reanalyses (PMID 30398520)

Sources and publication status checked November 3, 2026. The correction was read with the primary report; the small event count is central to the appraisal.

For education, not personal medical advice. Nutrition and supplement decisions during cancer care should be individualized with the oncology and dietetics teams.