Despite the fact that breast cancer (BC) is the most common cancer among women worldwide and the importance of diet as a key modifiable risk factor for many chronic diseases, the evidence on the effect of individual dietary factors on BC risk, apart from alcohol, is inconclusive. Some authors argue that focusing on overall dietary patterns, instead of on individual foods or nutrients, may better capture variability in the population’s diet while allowing the evaluation of interactions between the dietary factors.

Using 1017 incident cases of BC, diagnosed in the Oncology departments of 23 hospitals included in the GEICAM Spanish Breast Cancer Research Group, (http://www.geicam.org/) and their individually matched healthy controls from the same town and of similar age (± 5 years), this study explored the association between dietary patterns and BC risk in Spanish women according to menopausal status and intrinsic tumor subtype. Cases were sub classified as:

1. Luminal tumors (Estrogen Receptor (ER) and/or Progesterone Receptor (PR) positive with Human Epidermal Growth Factor (HER2) negative),
2. HER2 positive tumors (HER2+ irrespective of ER or PR results); and 3. Triple negative tumors (ER-, PR- & HER2-). Postmenopausal status was defined as absence of menstruation in the last 12 months.

   Cases and controls completed a structured questionnaire collecting information on demographic and anthropometric characteristics, personal and family history, past physical activity and dietary intake in the last five years (food frequency questionnaire-FFQ).The 117-item semi-quantitative FFQ items were reduced to 26 food groups excluding non-caloric and alcoholic beverages. Major existing dietary patterns were identified in the controls by applying Principal Components Analysis (PCA). For each retained pattern, a score was calculated for cases and controls that measured the level of compliance with each pattern.

   The association between dietary patterns and BC in general and according to menopausal status and intrinsic tumor subtypes (Luminal, HER2+, Triple Negative) was evaluated using logistic and multinomial regression models.

The PCA evidenced three different dietary patterns:

• Western pattern, characterized by high intakes of high-fat dairy products, processed meat, refined grains, sweets, caloric drinks, and other convenience foods and sauces, and by low intakes of low-fat dairy products and whole grains;
• Prudent pattern, that denoted high intakes of low-fat dairy products, vegetables, fruits, whole grains, and juices; and • The Mediterranean pattern, with high intakes of fish, vegetables, legumes, boiled potatoes, fruits, olives and vegetable oil, and low intake of juices.

Protective effect of the Mediterranean diet on breast cancer risk

A higher Western pattern score was positively associated with BC, with the odds ratio (OR) for the top versus the bottom quartile being 1.46 (95%CI=1.04-1.31). This association was stronger in premenopausal women (OR=1.75; 95%CI=1.14-2.67). Conversely, a higher Mediterranean score implied a lower BC risk (OR=0.56; 95%CI=0.40-0.79). In both cases, the linear dose-response trend was statistically significant. Interestingly, the protective effect of the Mediterranean pattern was stronger for triple negative tumors (OR for the fourth quartile=0.32; 95%CI= 0.15-0.66)), with a steeper dose-response trend compared to other subtypes (p-value of heterogeneity =0.04). No association with BC was found for the Prudent pattern.

Diet is a modifiable risk factor, therefore, the identifi cation of harmful and beneficial dietary habits and the characterization of the population most susceptible to such habits is essential for the design of BC prevention policies. The results of this study provide novel information in these two fronts since the beneficial effect of a diet reach in fruits, vegetables, legumes, oily fish and vegetable oils over a diet low in calorie and fat intake is still debated, even in the scientific community. The study also identified a higher detrimental effect of Western dietary habits in younger women, pinpointing them as a main target for future preventive policies. Finally, according to the results, the Mediterranean diet appears particularly beneficial against triple negative tumors.

Based on: Castelló A, Pollán M, Buijsse B, Ruiz A, Casas AM, Baena-Cañada JM, Lope V, Antolín S, Ramos M, Muñoz M, Lluch A, de Juan-Ferré A, Jara C, Jimeno MA, Rosado P, Díaz E, Guillem V,
Carrasco E, Pérez-Gómez B, Vioque J, Boeing H, Martín M; GEICAM researchers. Spanish Mediterranean diet and other dietary patterns and breast cancer risk: case-control EpiGEICAM study. Br J Cancer