Fruits, Vegetables, Plant-based Diets, and Breast Cancer

Abstract

Breast cancer is the most common type of malignancy among women, and incidence rates have been rising in recent years and are expected to continue increasing. Diet is thought to play a role in breast tumorigenesis; healthy plant foods, including fruits and vegetables, and healthy plant-based diets have been associated with reduced risk of breast cancer. These results appear to vary by hormone receptor status, and there is inconclusive evidence on whether these results differ by molecular subtype. Recent advances in ‘omics technology have allowed for the development of methods to measure levels of metabolites present in food or reflective of biological response to dietary intake. Few studies have explored circulating metabolites, especially unidentified metabolomic features, related to fruit and vegetable consumption and risk of breast cancer. In Chapter 1, we used plasma metabolite values measured in nested case control studies from the Nurses’ Health Study (NHS) and NHSII to develop a metabolomic signature of fruit and vegetable intake. We examined associations between the metabolomic signatures and dietary fruit and vegetable intake with breast cancer risk. In this study, we identified metabolomic signatures reflecting fruit and vegetable consumption and underlying biological processes that may link diet with breast cancer. In Chapter 2, we pooled data from 28 cohorts in the Pooling Project of Prospective Studies of Diet and Cancer (DCPP). Associations between fruit and vegetable intakes and breast cancer risk were assessed. Higher fruit intake was inversely associated with all subtypes of breast cancer, with the strongest associations observed for ER-negative and triple-negative breast cancer. Higher vegetable intake was associated with lower rates of ER-negative and triple-negative tumors. Results were generally consistent across studies and strata defined by sociodemographic, medical, lifestyle, and study characteristics. These results provided additional evidence supporting consumption of fruits and vegetables for cancer prevention. In Chapter 3, we investigated relationships between the healthy plant-based dietary index (hPDI) and unhealthy PDI (uPDI) and breast cancer risk overall and by subtypes among 27 cohorts in the DCPP. The hPDI was significantly associated with lower incidence of overall, ER-positve, ER-negative, HER2-enriched, and triple-negative breast cancer. The uPDI was significantly associated with higher incidence of overall and ER-negative tumors. Weaker and nonsignificant results were observed for the remaining subtypes. These findings suggest that healthful plant-based diets were associated with a slightly lower incidence of breast cancer, particularly ER-negative tumors, and unhealthful plant-based diets were associated with higher incidence of the same subtypes.