Plain language summary
Epidemiological evidence suggests that eating a Mediterranean diet is associated with a reduced risk of breast cancer. The aim of this review, which includes seven epidemiological studies, was to examine the association between a Mediterranean diet and risk of breast cancer according to molecular subtype: oestrogen-receptor (ER) and progesterone-receptor (PR) status and human epidermal growth factor 2 (HER2) oncogene expression. The authors define a Mediterranean diet as high in fruit and vegetables, fish, whole grains, nuts, seeds and olive oil; low to moderate in alcohol, dairy products, eggs, and poultry; and low in red and processed meats and sweets. The authors find that eating a Mediterranean diet is associated with a reduced risk of breast cancer in postmenopausal women, particularly among ER negative tumours, with a less clear association for other subtypes and premenopausal women.
Abstract
BACKGROUND Previous observational studies and systematic reviews have suggested that adherence to the Mediterranean diet is associated with a reduced risk of breast cancer, but have not examined associations with molecular subtypes of breast cancer. The current review examines the association with adherence to the Mediterranean diet and risk of breast cancer according to molecular subtypes. METHODS Bibliographic searches were conducted in PubMed and CINAHL using relevant MeSH search terms and Boolean algebra commands. RESULTS Six cohort studies and one case-control study have examined adherence with the Mediterranean diet and risk of breast cancer according to estrogen-receptor (ER) and progesterone-receptor (PR) status and human epidermal growth factor 2 (HER2) oncogene expression. Taken overall, studies suggest that the Mediterranean dietary pattern is inversely associated with breast cancer risk in postmenopausal women, and that the inverse association is somewhat stronger among ER- tumors. Although there is a suggestion that the Mediterranean diet is inversely associated with PR- tumors and with ER-/PR-/HER2- ("triple negative" tumors), results to date have been mixed and the number of studies that have examined associations with this dietary pattern among tumors characterized by multiple molecular subtypes remains small. CONCLUSIONS The results of this systematic review suggest that consumption of a Mediterranean diet pattern is associated with a reduced risk of postmenopausal breast cancer, particularly among ER- tumors. Additional cohort studies that have sufficient sample sizes and long-term follow-up are warranted to identify sizeable numbers of invasive breast cancer cases, thereby allowing for characterization of the tumors by molecular subtype.
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