This study is being done to better understand how time restricted eating (eating all food in an 8 hour window) can help a person receiving chemotherapy treatment for breast cancer, stages I-IV. The aim is to find out if time restricted is feasible and acceptable to individuals starting chemotherapy for breast cancer. We will test 3 different eating window options compared to a control group for 24 weeks.

Little is known about how nutrition therapy can affect breast cancer treatment outcomes. Current standard care suggests enough daily calories and protein to maintain body weight and avoid muscle loss. However, this approach may be antiquated given weight gain is common during treatment and emerging pre-clinical and clinical evidence suggest that fasting during chemotherapy may improve clinical and patient-reported outcomes. For example, preliminary human trials examining the fasting mimicking diet (very low-calorie, low-protein diet 1-week per month) or short-term fasting (48-120 hours (h)), known as periodic fasting, surrounding chemotherapy may increase effectiveness of treatment and decrease side effects related to chemotherapy. Yet these diets have low adherence, side effects of their own, and may increase patient burden and decrease quality of life. In contrast, time restricted eating (TRE) is a form of intermittent fasting with high adherence that may have similar positive effects on treatment outcomes without the untoward side-effects. Moreover, TRE may have beneficial effects on glucose regulation and body composition (i.e., decreased weight and body fat gain) suggesting the potential importance of this regimen to breast cancer recurrence. TRE is extremely accessible with no calorie counting or financial burden to the patient, individuals just shorten their eating window daily.

The aim of this trial is to examine the feasibility and acceptability of 24-weeks of 8-h TRE among female breast cancer patients initiating chemotherapy. Additionally the preliminary effect of 8-h TRE on treatment outcomes, treatment related side-effects, and patient reported quality of life and fatigue will be explored. Exploratory outcomes will include glucose regulation, body weight, body composition, IGF-1, IGFBP3, SHBG, estradiol (e2), TNF-alpha, and hsCRP

Inclusion Criteria:

• Age 25-99 at time of consent
• English language or Spanish language (based on availability of lab interpreters)
• ECOG 0 or 1
• Breast cancer to meet histologically confirmed Stage I-III or Stage IV with Medical Oncology approval.
• Demonstrates adequate organ function (absolute neutrophil count ≥ 1,500/μL).
• All screening labs to be obtained within 30 days prior to registration.
• Able to provide written informed consent and HIPAA authorization for release of personal health information, via an approved UIC Institutional Review Board (IRB) informed consent form and HIPAA authorization.
• Women of childbearing potential must not be pregnant or breast-feeding. A negative serum or urine pregnancy test is required per institutional practice guidelines.
• As determined at the discretion of the enrolling physician or protocol designee, ability of the subject to understand and comply with study procedures for the entire length of the study.

Exclusion Criteria:

• Women with type 1 or insulin dependent type 2 diabetes
• Women with BMI > 45kg/m2 and < 18.5 kg/m2
• Women who are pregnant or nursing. A negative serum or urine pregnancy test is required per institutional practice guidelines.
• Shift workers
• Women with a history of eating disorders
• Enrolled participants with a significant weight loss or weight gain within 3 months of the study (weight gain or loss >4kg)
• Uncontrolled HIV/AIDS or active viral hepatitis
• Any prior malignancy <5 years, chemotherapy within the last year or concurrent malignancy whose natural history or treatment has the potential to interfere with the safety or efficacy assessment of this investigational regimen, as determined by the treating medical oncologist.
• Breast cancer recurrence classified by the treating medical oncologist
• Any mental or medical condition that prevents the patient from giving informed consent or participating in the trial.
• Other major comorbidity, as determined by study PI
• Illicit drug use within previous 3 months or excessive use of alcohol (i.e., > 2 drinks/day)
• Currently participating in Weight Watcher's or another weight loss program, including weight loss medication such as GLP-1 medications.
• Myocardial infarction
• Congestive heart failure
• Chronic hepatitis
• Cirrhosis
• Chronic pancreatitis
• History of solid organ transplantation

data collectors and sample analysis will be blinded to arm allocation