INCLUSION CRITERIA: Participants must have histologically or cytologically confirmed unresectable melanoma that has not been treated with any systemic therapy. Participants must be planning to undergo treatment with anti-PD1/PDL1 monotherapy.  Note: This anti-PD1/PDL1 monotherapy is permissible to have started up to 14 days prior to completion of baseline assessments on this study to still be eligible for enrollment.  Participants must have measurable disease, per RECIST 1.1. Age greater than or equal to 18 years and English speaking. English-language ability is required because a portion of the study involves reading and responding to English-language questionnaires, along with creating a free response spoken answer to a question, where the information will be transcribed and analyzed. Willingness and capability to comply with diet and exercise prescriptions, use the MyFitnessPal app, wear the Garmin (trademark) device, complete surveys, and provide stool samples. Participants must own a smartphone capable of running the MyFitnessPal and  Garmin Connect (trademark) apps.  ECOG performance status <2 (Karnofsky >60%,). BMI 18.5 -35 kg/m2 The ability of the subject to understand and the willingness to sign a written informed consent document.  EXCLUSION CRITERIA:  Participants who are receiving any other investigational agents. Any concurrent malignancy that requires active systemic therapy Any health condition that requires treatment with cytotoxic chemotherapy or targeted therapy Medical contraindications to the study diet and/or exercise prescriptions as determined by a physician Self-reported dietary and/or exercise restrictions that would preclude adherence to the study diet and exercise prescriptions Systemic antibiotic use within the past 30 days Use of probiotic supplements (probiotic foods such as yogurt, kefir, sauerkraut, etc., are permissible), fiber supplements, bile acid sequestrants, weight loss supplements, or appetite suppressants within the last 30 days. Women known to be pregnant or lactating are excluded from the study because it is unknown if the study diet and exercise prescriptions may have deleterious effects on the child and/or mother in the context of pregnancy/breastfeeding. Current smoker or < 8 weeks since smoking cessation. There is evidence that smoking may alter the microbiome. Heavy drinker defined as >14 alcoholic drinks per week Current illicit drug use. There is evidence that illicit drug use may alter the microbiome. Diagnosis of diabetes mellitus type I or II that requires treatment Uncontrolled intercurrent illness including, but not limited to, symptomatic congestive heart failure, unstable angina pectoris, cardiac arrhythmia, or psychiatric illness/social situations that would limit compliance with study requirements.