The prevalence of obesity has increased rapidly in recent years. Epidemiological studies since the 1970's have strongly suggested that excess body weight gain may be a major risk factor for many cancers including breast cancer. In addition, once diagnosed with breast cancer, women who are overweight or obese experience worse outcomes despite standard local and adjuvant therapy. Furthermore, most women gain weight following a diagnosis of breast cancer, and this weight gain may increase risk of recurrence by 40-50% and breast cancer-related mortality by 53-60%.