Romanos-Nanclares A, Willett WC, Rosner BA, et al. - This study was intended to evaluate whether healthful and unhealthful plant-based diets were associated with the risk of breast cancer in U.S. women. In this study, 76,690 women from the Nurses' Health Study (NHS,1984-2016) and 93,295 women from the Nurses' Health Study II (NHSII,1991-2017) were prospectively followed. They evaluated the adherence to an overall plant-based diet index (PDI), a healthful PDI (hPDI), and an unhealthful PDI (uPDI) using previously developed indices. They used Cox proportional hazards models to calculate HR and 95% CIs for incident invasive breast cancer. This research gives evidence that adherence to a healthful plant-based diet may decrease the risk of breast cancer, particularly those that are more likely to be aggressive tumors. This is the first prospective research to evaluate the relation between healthful and unhealthful plant-based dietary indices and the risk of total and subtype-specific breast cancer.