Diet and Immune Effects Trial: DIET- A Randomized Double Blinded Dietary Intervention Study in Patients With Metastatic Melanoma Receiving Immunotherapy

PRIMARY OBJECTIVE: To establish the effects of dietary intervention on the structure and function of the gut microbiome. SECONDARY OBJECTIVES: 1. Assess the effects of dietary intervention on gut metabolic output and systemic metabolism. 2. Assess the effects of dietary intervention on systemic and tumor immunity 3. Determine the safety (AEs) and tolerability (GSRS-IBS) of the dietary intervention 4. Assess the rate of immune related adverse events in patients on immunotherapy receiving dietary interventions 5. Determine the maximum daily fiber content that 70% of participants are able to tolerate 6. Assess the adherence to the dietary interventions as defined by 70% of calories consumed over the duration of the study being derived from provided diets (as measured by food records) 7. Assess the effects of dietary interventions on quality of life and other patient reported outcomes (PROs) EXPLORATORY OBJECTIVES: 1. Assess the association of dietary interventions with clinical outcomes (objective response rate \[ORR\] and progression-free survival \[PFS\] rate in unresectable cohort and recurrence rate \[RR\] in adjuvant cohort). 2. Explore predictors of biological response to dietary interventions. OUTLINE: Patients are randomized to 1 of 2 arms. ARM I (ISOCALORIC HIGH-FIBER DIET): Patients receive a whole foods diet that follows the recommended American Cancer Society guidelines but is higher in fiber for 11 weeks. ARM II (ISOCALORIC CONTROL DIET): Patients receive a standard whole foods diet of recommended by the American Cancer Society for 11 weeks. After completion of study, patients are followed up at 12 weeks.