Impact of Ketogenic Diet on Tumor Microenvironment in Patients With Breast Cancer

Inclusion Criteria: * Be willing and able to provide consent for the study * Age ≥ 18 on the day consent is obtained * Eastern Cooperative Oncology Group (ECOG) score ≤ 2 * Patients must be postmenopausal the time of study entry * Stage I or II breast cancer using Tumor, Nodes and Metastasis (TNM) stage groups per American Joint Committee on Cancer (AJCC) 8th edition * Plan for upfront breast surgery with mastectomy or partial mastectomy and does not require pre-operative systemic therapy per standard of care * Must have tissue available from initial breast biopsy performed per standard of care * have the ability in the opinion of the investigator to adhere to a ketogenic diet and comply with study requirements such as ability to participate in telemedicine, utilize apps on a smart device, measure glucose/ketones at home, accurately log food intake and exercise, prepare food that is in line with ketogenic diet Exclusion Criteria: * Clinical indication for neoadjuvant therapy * Partial mastectomy or mastectomy planned for less than 3 weeks from study entry * Inability to comply with ketogenic diet * Consistent use of ketogenic diet within past 3 months * Participation in another diet program during study period * Nonepithelial breast malignancy such as sarcoma or lymphoma * Body Mass Index \< 18.5 * Comorbidities and/or active or ongoing illness that in the opinion of the investigator will limit patient's ability to safely participate in study * Type I diabetes * Use of insulin or other oral hypoglycemic drugs for diabetes * Has had any of the following within the past 6 months * Myocardial infarction or unstable angina * Ventricular arrythmia * Acute decompensated heart failure * Cerebrovascular accident * Hypertensive emergency * Uncontrolled hypertension despite antihypertensive use * End-stage renal, liver, or cardiac disease * genetic disorders that affect lipid metabolism (example: pyruvate carboxylase deficiency, porphyria, primary carnitine deficiency, carnitine palmitoyltransferase I or II deficiency, carnitine translocase deficiency, beta-oxidation defects, among others) * G6PD (glucose-6-phosphate dehydrogenase) deficiency * Malabsorption syndromes (such as but not limited to inflammatory bowel disease, history of gastric sleeve, prior bowel resection) * History of recurrent kidney stones or predisposition to kidney stones * Triglycerides ≥ 500 * Has known psychiatric or substance use disorders that would interfere with participation in the study