Currently the Department of Health and Human Services, the American Cancer Society and others provide diet and exercise guidelines for cancer survivors. Many women with breast cancer do not follow these guidelines, and also elect to delay concerted efforts toward following them until active treatment is complete. However, adoption of these recommended lifestyle behaviors soon after diagnosis may prevent adverse changes in body composition and breast cancer biomarkers and may even improve the efficacy of treatment resulting in improved breast cancer prognosis. Further, by increasing our understanding of the mechanisms mediating the association between lifestyle behaviors and breast cancer survival, this study will improve our knowledge of how changes in diet and physical activity influence breast cancer outcomes. Lastly, guidelines for breast cancer survivors also overlap with those for diabetes and cardiovascular disease (CVD) prevention, the latter being a common cause of breast cancer mortality.