Pro-vegetarian dietary pattern and risk of breast cancer: a case–control study

Background There are a few conflicting results from studies assessing the association between plant-based diets, particularly pro-vegetarian dietary pattern (PDP), and breast cancer (BC) incidence. Therefore, this study aimed to investigate the association between PDP and BC odds in the Iranian population. Methods This case–control study was conducted on 134 women with BC and 265 without cancer (control). Participants were selected from two referral hospitals in Tehran, Iran. Also, a validated food frequency questionnaire was used to collect food information. Logistic regression was used to assess the association between PDP and BC and the association between PDP and BC by menopausal status. Results It was observed that in two models of logistic regression, the chance of BC was lower in the second and last tertile (T) than in the first tertile of PDP (model 1—T 2 : odds ratio (OR) = 0.39; 95% confidence interval (CI): 0.23–0.67; P = 0.001, and T 3 : OR = 0.43; 95% CI: 0.26–0.73; P = 0.002—model 2: T 2 : OR = 0.42; 95% CI: 0.24–0.74; P = 0.003, and T 3 : OR = 0.49; 95% CI: 0.27–0.88; P = 0.017). Also, according to menopausal status, the odds of developing BC in post-menopausal women in the second and last tertile of PDP was significantly lower than the first tertile in both logistic regression models. Conclusions The findings revealed that Iranian women who followed PDP had a lower chance of developing BC. Also, we found that a diet high in plant-based foods and low in animal products is beneficial for reducing BC odds, particularly for post-menopausal women.