Fruit and vegetable intervention in lactating women to reduce breast cancer risk: effects on breast cell DNA methylation, breast inflammation, and weight Mechanistic data show that compounds in fruits and vegetables have anti-inflammatory and anti-carcinogenic properties that can reduce breast cancer risk. However, observational and interventional studies have provided mixed results, and a recent report by the American Institute for Cancer Research (AICR) concludes that the data are insufficient but suggestive that non-starchy vegetables and foods containing carotenoids reduce risk. Measurement error, relatively low levels of carotenoid-rich fruit and vegetable intake in the study populations, emphasis on diet in later adulthood, and confounding factors likely contribute to the weak associations. Therefore, we will conduct a randomized diet intervention trial in young women to assess the extent to which at least 8 to 10 daily servings of deeply pigmented and nutrient dense fruits and vegetables reduces biomarkers of breast cancer risk. The intervention is focused on breastfeeding women because: 1) pregnancy and lactation are normal early life course events; 2) the risk of pregnancy-associated breast cancer (PABC) is increased for up to 10 years postpartum; 3) a dietary intervention to reverse the detrimental molecular changes associated with puberty and pregnancy is more likely to be successful in younger than in older women; 4) a diet rich in fruits and vegetables is hypothesized to reduce the inflammation during lactation/weaning and lower PABC risk; 5) postpartum lactating women may be a highly motivated population; and 6) breastmilk provides access to the breast microenvironment and breast epithelial cells to noninvasively assess the diet intervention directly in the breast. Four hundred nursing mothers will be randomly assigned to either the intervention arm, in which they are asked to increase fruit and vegetable intake to at least 8 to 10 daily servings for one year, or to a control condition in which participants receive a dietary guideline for breastfeeding mothers. Women in the intervention arm will receive counseling and boxes of fruits and vegetables for the first 20 weeks, after which they will continue to receive counseling. Changes in DNA methylation and cytokine profiles in breastmilk will be evaluated. Maternal weight and body fat distribution, and infant growth will be monitored. These results will greatly expand our knowledge of how diet alters molecular pathways in a specific organ, ultimately contributing to both breast cancer etiology and prevention. Additionally, objective favorable results observed in the breasts of young women can potentially contribute to important behavior changes aimed at reducing risk.