Prolonged Nightly Fasting in Breast Cancer Survivors

Inclusion Criteria:

* Participants must have a documented history of histologically confirmed invasive breast cancer.
* Participants with a history of stage I to III invasive breast cancer, and no current evidence of disease.
* A history of bilateral breast cancer is allowed provided the patient is currently disease free, with stage I to III disease on both sides.
* No evidence of distant metastatic disease or unresectable locally recurrent disease
* All adjuvant or neoadjuvant cytotoxic chemotherapy, radiation, and surgery for breast cancer must have been completed at least 6 month prior to registration. Except:

  * Adjuvant hormonal therapy is permitted. Must have been on for a minimum of 1 month.
  * Adjuvant trastuzumab, pertuzumab, TDM1, or neratinib for Her2 positive breast cancer is permitted Age ≥18 years.
* Participant must be female.
* Ability to understand and the willingness to sign a written informed consent document

Exclusion Criteria:

* Distant metastatic breast cancer (Stage IV breast cancer) or unresectable locally recurrent disease
* Participants with diabetes mellitus.
* Participants with a pre-existing eating disorder (anorexia nervosa, bulimia)
* Participants with a BMI\< 19kg/m2 or a weight loss of 5% in the last month or 10% in the last 3 months.
* Participants using weight loss medications at the time of study enrollment.
* Participants using oral steroids at the time of enrollment.
* Participants who are receiving any other investigational agents. Participants with uncontrolled intercurrent illness.
* Participants with psychiatric illness/social situations that would limit compliance with study requirements.
* Pregnant women are excluded from this study because the effects of prolonged fasting on the fetus are not known.