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