Spanish Mediterranean diet and other dietary patterns and breast cancer risk: case-control EpiGEICAM study

Background: Although there are solid findings regarding the detrimental effect of alcohol consumption, the existing evidence on the effect of other dietary factors on breast cancer (BC) risk is inconclusive. This study aimed to evaluate the association between dietary patterns and risk of BC in Spanish women, stratifying by menopausal status and tumour subtype, and to compare the results with those of Alternate Healthy Index (AHEI) and Alternate Mediterranean Diet Score (aMED). Methods: We recruited 1017 incident BC cases and 1017 matched healthy controls of similar age (+/- 5 years) without a history of BC. The association between 'a priori' and 'a posteriori' developed dietary patterns and BC in general and according to menopausal status and intrinsic tumour subtypes (ER+/PR+ and HER2-; HER2+; and ER-/PR- and HER2-) was evaluated using logistic and multinomial regression models. Results: Adherence to the Western dietary pattern was related to higher risk of BC (OR for the top vs the bottom quartile 1.46 (95% CI 1.06-2.01)), especially in premenopausal women (OR = 1.75; 95% CI 1.14-2.67). In contrast, the Mediterranean pattern was related to a lower risk (OR for the top quartile vs the bottom quartile 0.56 (95% CI 0.40-0.79)). Although the deleterious effect of the Western pattern was similarly observed in all tumour subtypes, the protective effect of our Mediterranean pattern was stronger for triple-negative tumours (OR = 0.32; 95% CI 0.15-0.66 and P-heterogeneity = 0.04). No association was found between adherence to the Prudent pattern and BC risk. The associations between 'a priori' indices and BC risk were less marked (OR for the top vs the bottom quartile of AHEI = 0.69; 95% CI 0.51-0.94 and aMED = 0.74; 95% CI 0.46-1.18)). Conclusions: Our results confirm the harmful effect of a Western diet on BC risk, and add new evidence on the benefits of a diet rich in fruits, vegetables, legumes, oily fish and vegetable oils for preventing all BC subtypes, and particularly triple-negative tumours.