Plant-based dietary patterns and risk of breast cancer: A systematic review and meta-analysis

Plant-based dietary patterns have garnered increasing attention for their potential in chronic disease prevention, including cancer. However, the association between adherence to plant-based diets and breast cancer risk remains uncertain. This systematic review and meta-analysis evaluated the relationship between breast cancer incidence and three validated plant-based diet indices: the overall plant-based diet index (PDI), the healthy PDI (hPDI), and the unhealthy PDI (uPDI), which distinguish between healthful and less healthful plant-derived foods. A comprehensive search of PubMed, Embase, and Web of Science through August 2025 identified seven observational studies encompassing 44,680 participants. Studies were eligible if they reported associations between PDI, hPDI, or uPDI and breast cancer risk. Random-effects meta-analyses were conducted to estimate pooled hazard ratios (HRs) or odds ratios (ORs), with subgroup analyses stratified by menopausal and estrogen receptor (ER) status. Heterogeneity was assessed using the I² statistic. This review was registered in PROSPERO (ID: CRD420251127355). Meta-analysis showed that higher adherence to the hPDI was associated with a significant reduction in breast cancer risk (HR = 0.88; 95% CI: 0.81-0.95), with a modest benefit also observed for overall PDI (HR = 0.90; 95% CI: 0.84-0.96). No statistically significant association was found for uPDI (HR = 1.05; 95% CI: 0.98-1.14). Protective associations were stronger in premenopausal women and ER-positive subtypes. These findings suggest that adherence to high-quality, nutrient-dense plant-based diets may lower breast cancer risk. Distinguishing between healthful and unhealthful plant-based foods is essential for developing effective dietary strategies for cancer prevention.