Dietary patterns, which represent the amounts, proportions, variety or combinations of different foods and drinks in the diets, and the frequency with which they are regularly consumed, have been linked to the risk of numerous cancers. However, the association between dietary patterns and breast cancer risk is still unclear. This systematic review was conducted to investigate and clarify the association between dietary patterns and breast cancer risk by assessing and appraising the literature published to date and evaluating the results of these studies. A broad, general and inclusive electronic literature search was conducted throughout the Google Scholar, and PubMed databases to identify studies written in English and published from 2001 to 2017. 2,215 articles were found and 112 articles were chosen for further review, of which 87 articles were excluded after reviewing the title and abstract of each article. The remaining 25 articles were included in the paper after a full review. Although in most of the articles included in this paper, no overall association was reported between the prudent, Mediterranean or Western dietary patterns and breast cancer risk, it was suggested that a Western or Western-type dietary pattern might increase the risk of breast cancer, and a prudent, Mediterranean and healthy dietary patterns might protect against estrogen receptive-negative tumors, mostly in postmenopausal women. This systematic review provides evidence of an association between dietary patterns and breast cancer risk and highlights the need for further observational and interventional studies.

Cancer is a major public health concern among women in the United States of America. Approximately 40% of American women are diagnosed with some type of non-dermatologic cancer during their lifetime and despite all the new advancements in detection and treatment, breast cancer remains the second leading cause of mortality for women in the United States. Every year, more than 200, 000 women in the U.S. are diagnosed with aggressive breast cancer. The etiology of breast cancer is considered multifactorial, and includes interactions between genetic, behavioral, and environmental factors. Some well-established and strong risk factors for breast cancer such as: age, family and reproductive history, height reached by the adulthood, and exposure to high doses of ionizing radiation are not modifiable; however, the adaptable lifestyle factors including diet, smoking status, physical activity, alcohol consumption, as well as body size and shape, that are directly associated with breast cancer risk, occurrence, recurrence, and mortality rate, are easier to modify. Therefore, the American Cancer Society Nutrition and Physical Activity Guidelines Advisory Committee have issued an inclusive set of recommendations to help promote health for cancer survivors through health behavior adjustments. According to these data, since many health behaviors occur in combination, a compound variable might be needed to capture how lifestyle factors act synergistically to influence the development of breast cancer and all-cause mortality. Based on the findings of several studies, steady positive associations have been found between a combined lifestyle variable and both breast cancer risk and all-cause mortality rates. 

There are potential limitations to this systematic review. The pooled results discussed in this paper, are directly retrieved from the included studies, which have their own individual strengths and weaknesses in terms of study design. It is also possible that there may have been a misclassification within the healthy, prudent and Mediterranean dietary patterns in the articles reviewed in this paper. The healthy, prudent and Mediterranean dietary patterns included in this paper, all contained high consumption of plant-based foods and low consumption of red, high-fat and processed meat, which are the recommended dietary patterns suggested by the American Cancer Society to prevent cancer across the populations. There are disadvantages to this type of analysis. Since the exact amount of consumption of individual foods in the prudent, Mediterranean, and healthy dietary patterns were not exactly identical among the studies in this paper, it could have led to some misclassification errors. Even very small measurement errors can dramatically affect the measures of the risk for a disease; therefore, it is possible that the small inverse association observed could have been due to a combination of dietary measurement errors and misclassification of women into the dietary pattern categories. In order to minimize the risk of bias, the authors of the selected articles generally discussed the most commonly identified dietary patterns across the populations. Therefore, other types of dietary patterns that could be relevant to breast cancer risk were not included in this review. The tools used to collect dietary information in this systematic review were also different among the studies. Although the food frequency questionnaire was used in most cases, this tool is known to be subject to measurement errors. Therefore, it is not the most reliable tool to detect a significant association between a dietary pattern and breast cancer risk. In conclusion, Western or Western-type dietary patterns which mainly include high consumption of red meat products, French fries, appetizers, rice, pasta, potatoes, pizza, pies, canned fish, eggs, alcoholic beverages, cakes, mayonnaise, and butter/cream; are positively associated with breast cancer risk. Adherence to healthy, Mediterranean, and prudent dietary patterns, which essentially include vegetables, fruits, seafood, poultry, nuts, legumes, olive oil, and sunflower oil; on the other hand, are negatively associated with breast cancer risk in postmenopausal women, and this association is stronger in estrogen receptor-negative tumors. Therefore, adherence to a diet containing mostly fruits, vegetables, fish, nuts, and olive/sunflower oil, along with avoidance of Western-type foods, may contribute to a significant reduction in postmenopausal breast cancer risk. The results of this systematic review support the potential chance for breast cancer prevention through dietary modifications. These results also highlight the need for further observational and interventional studies to explain the role of dietary patterns and breast cancer risk across populations.

With Regards,
Joseph Kent
Journal Manager
Journal of Clinical Nutrition & Dietetics