The association between plant-based diet indices and the risk of breast cancer: a case-control study.

Background: Previous studies examining the relationship between plant-based diets and breast cancer (BrC) have provided conflicting evidence. To address these inconsistencies, we aimed to evaluate the association between the plant-based diet index (PDI), healthful PDI (hPDI), and unhealthy PDI (uPDI) with the odds of BrC in Iranian women.

Methods: The current case-control research was performed on 133 Iranian women with BrC and 265 controls. The study subjects were selected from hospitals in Tehran. PDI, hPDI, and uPDI were categorized into eighteen food groups based on nutrient composition similarity. The relationship between PDIs and BrC was assessed using logistic regression.

Results: After adjusting for confounding factors, the chance of developing BrC was lower in the highest tertile of hPDI compared to the lowest tertile (odds ratio (OR) = 0.495; 95% confidence interval (CI): 0.274-0.891; P = 0.019). In addition, postmenopausal women in the second and last tertiles of hPDI had lower odds of BrC than those in the first tertile (T) (T₂: OR = 0.342; 95% CI: 0.141-0.828; P = 0.017- T₃: OR = 0.262; 95% CI: 0.107-0.639; P = 0.003) in the adjusted model. Furthermore, in premenopausal women in the highest tertile of uPDI, the odds of BrC were increased compared to the lowest tertile (OR = 2.546; 95% CI: 1.051-6.167; P = 0.038) in the adjusted model.

Conclusions: Adherence to a healthy plant-based dietary pattern, including vegetables, fruits, whole grains, nuts, and legumes, seems to be beneficial for BrC prevention, particularly in postmenopausal women. Future prospective cohort studies that consider menopausal status and the type of BrC are needed to support these findings.