BREADS: Breast Adjuvant Diet Study

Inclusion Criteria: * Histologically confirmed breast cancer * Planning to start adjuvant hormonal therapy using an aromatase inhibitor or has started adjuvant hormonal therapy using an aromatase inhibitor * Able to read, write, and understand English * BMI ≥ 24 kg/m2 * Age ≥ 18 years * ER and/or PR positive (defined as having ≥ 1% staining for ER and/or PR on IHC) * Post-menopausal * The absence of menstrual cycles in women who have not undergone hysterectomy for at least 12 months preceding cancer diagnosis OR * History of a bilateral oophorectomy OR * History of a hysterectomy and age \>55 OR * No menses for \<1 year with FSh and estradiol levels in postmenopausal range according to institutional standards * ECOG Performance Status 0 or 1 * Female * Written informed consent obtained from subject and ability for subject to comply with requirements of the study Exclusion Criteria: * Use of hormonal therapy other than aromatase inhibitors * History of other malignancy within the past 5 years, except for malignancies with a \> 95% likelihood of cure (e.g. thyroid cancer, non-melanoma skin cancer) * Already consuming a severe carbohydrate restricted (\<20 g carbohydrates per day) diet or vegetarian diet * Currently on or plans to start chemotherapy (HER2/neu targeted therapy okay) * Medical comorbidities that in the opinion of the investigator limits the patient's ability to complete the study * Symptomatic metastases (Metastases allowed if asymptomatic) * Current use of appetite suppressant medications * Current use of any weight loss medications including herbal weight loss supplements or if patients are enrolled in a diet/weight loss program