Plant-based dietary patterns and breast cancer risk in the European prospective investigation into cancer and nutrition (EPIC) study.

While previous literature suggests that plant-based diets may be associated with a lower risk of breast cancer, evidence remains inconsistent. In this study, we investigated the association between adherence to plant-based diets and breast cancer risk in the European Prospective Investigation into Cancer and Nutrition (EPIC) study. Overall plant-based diet index (PDI), healthful (hPDI), and unhealthful PDI (uPDI) were calculated, and multivariable Cox models were used to estimate hazard ratios (HR) and 95% confidence intervals (CI) of breast cancer for the three indices. Mediation analysis was performed to assess the role of body mass index (BMI) and waist circumference (WC) in the association between hPDI and postmenopausal breast cancer risk. Over a median follow-up of 14.9 years, 10,805 incident invasive breast cancer cases were identified among 258,343 women. In the multivariable model, not adjusted for BMI, higher adherence to hPDI was inversely associated with breast cancer risk, with HR per 1-SD increase [95% (CI)] of 0.97 (0.94, 0.99). The corresponding HRs (95% CI) per 1-SD increase for overall PDI and uPDI were 0.98 (0.96, 1.00) and 1.01 (0.99, 1.03), respectively. The associations between hPDI and postmenopausal breast cancer were partly explained by BMI and WC, which mediated 30% and 52% of this association, respectively. Higher adherence to hPDI was associated with a slightly lower total breast cancer risk. For postmenopausal breast cancer, this association was partly explained by lower BMI or WC. These findings suggest that promoting healthful plant-based diets could support breast cancer risk reduction.