Time Restricted Eating (TRE) in Metastatic Head and Neck Squamous Cell Cancer (mHNSCC) or Unresectable or Metastatic Renal Cell Carcinoma (RCC)

HNSCC Cohort Inclusion Criteria: 1. Histologically or cytologically confirmed recurrent/metastatic head and neck squamous cell cancer that is not amenable to local therapy with curative intent (surgery or radiation therapy with or without chemotherapy) and initiating standard of care immune checkpoint blocker- (Nivolumab, pembrolizumab, Atezolizumab, Avelumab or Durvalumab with or without chemotherapy), for the first time. 2. Patients must have measurable disease, defined as at least one lesion that can be accurately measured in at least one dimension (longest diameter to be recorded) as outlined in RECIST version 1.1. 3. Eastern Cooperative Oncology Group (ECOG) performance status of 0 to 1 4. Age ≥18 years, able to understand and voluntarily consent. Exclusion Criteria: 1. BMI \< 18.5. 2. Diabetes mellitus, pregnancy, any eating disorder including anorexia nervosa or bulimia. 3. Ongoing or active infection requiring iv antibiotics, autoimmune disease requiring systemic steroids greater than prednisone 60 mg equivalent, symptomatic congestive heart failure, unstable angina pectoris, insulin use, uncontrolled cardiac arrhythmia, or psychiatric illness/social situations that would limit compliance with study requirements. 4. Patients who have known leptomeningeal metastases or untreated or symptomatic brain metastases. Eligible patients must be neurologically asymptomatic and not requiring steroids. 5. Has received prior therapy with any anti-PD-1, anti-PDL-1 in a metastatic setting. 6. Patients for whom fasting is medically contraindicated RCC Cohort Inclusion Criteria: 1. Histologically or cytologically confirmed unresectable/metastatic clear cell renal cell carcinoma that is not amenable to local therapy with curative intent (surgery, radiation therapy, cryoablation, etc.,) and initiating standard of care systemic therapy consisting of immune checkpoint blockade (e.g. ipilimumab/nivolumab, cabozantinib/nivolumab, lenvatinib/pembrolizumab, or axitinib/pembrolizumab) for the first time. 2. Patients must have measurable disease, defined as at least one lesion that can be accurately measured in at least one dimension (longest diameter to be recorded) as outlined in RECIST version 1.1. 3. Eastern Cooperative Oncology Group (ECOG) performance status of 0 to 1 4. Age ≥18 years, able to understand and voluntarily consent. Exclusion Criteria: 1. BMI \< 18.5. 2. Diabetes mellitus, pregnancy, any eating disorder including anorexia nervosa or bulimia. 3. Ongoing or active infection requiring iv antibiotics, autoimmune disease requiring systemic steroids greater than prednisone 60 mg equivalent, symptomatic congestive heart failure, unstable angina pectoris, insulin use, uncontrolled cardiac arrhythmia, or psychiatric illness/social situations that would limit compliance with study requirements. 4. Patients who have known leptomeningeal metastases or untreated or symptomatic brain metastases. Eligible patients must be neurologically asymptomatic and not requiring steroids. 5. Has received prior therapy with any anti-PD-1, anti-PDL-1 6. Patients for whom fasting is medically contraindicated