Time-Restricted Eating and Cancer: Clinical Outcomes, Mechanisms, and Moderators

Inclusion Criteria: * Any sex/gender of any ethnic/racial background * Age greater than or equal to 18 years * Histologically-confirmed rectal cancer stage II, III, or IV (if curative) or human epidermal growth factor receptor 2-positive (HER2+) or triple negative breast cancer stage I, II, or III (only if definitive intent) per American Joint Committee on Cancer (AJCC) criteria * BMI 18.5 kg/m2 or greater * Receiving either neoadjuvant therapy with curative intent (breast cancer patients) or total neoadjuvant therapy with a 5-fluorouracil-based regimen and curative intent (rectal cancer patients) * Has completed ≤ 4 weeks of neoadjuvant treatment prior to study enrollment * Willing and able to adhere to the assessments, visit schedules, prohibitions, and restrictions Exclusion Criteria: * History of cytotoxic chemotherapy less than or equal to 12 months prior to rectal or breast cancer diagnosis * Allergic reaction to any of the treatment agents * Any prior pelvic radiotherapy * Currently active second malignancy other than non-melanoma skin cancers or cervical carcinoma in situ * History of GI perforation ≤12 months prior to enrollment * History of predisposing colonic or small bowel disorders with severe or rapidly worsening symptoms (not related to current cancer symptoms) * Receiving any parenteral nutrition or enteral (tube) feeding or using similar nutritional supplement during the study period * History of uncontrolled congestive heart failure defined as ew York Heart Association Class (NYHA) Class III or greater * Pre-existing grade ≥3 neuropathy * Currently participating in or has participated in a study of an investigational agent or investigational device ≤4 weeks of the first dose of treatment * Pregnant or breastfeeding * Currently perform overnight shift work more than one day/week on average * Strictly adhering to a \<10-hour eating window on most days * Known psychiatric or substance abuse disorders that would interfere with adhering to the requirements of the trial * Medical condition or laboratory abnormality that could impact participant safety or data validity, in the opinion of the medical investigators.