The proposed study will examine, in 250 women newly diagnosed with Stage I-III breast cancer who are not practicing the dietary and lifestyle guidelines, and who are scheduled to receive neoadjuvant or adjuvant chemotherapy, the effect of a 1-year dietary and physical activity guidelines intervention vs. usual care on the following breast cancer outcomes measured after surgery, but before beginning chemotherapy (Time 0), post chemotherapy (Time 1), at one-year post-diagnosis (Time 2), and at two years post-diagnosis (Time 3): adherence to treatment, and changes in biomarkers, body composition, and quality of life.