Intestinal Microbiome Modification With Resistant Starch in Patients Treated With Dual Immune Checkpoint Inhibitors

Inclusion Criteria: * Patients starting dual immune checkpoint inhibitor therapy (ipilimumab and nivolumab in any dose combination) for solid cancer treatment per FDA approved indications. * Ability to understand and the willingness to sign a written informed consent. Exclusion Criteria: * Patients with a history of colectomy and/or gastric bypass. * Patients with a known diagnosis of inflammatory bowel disease or irritable bowel syndrome. * Patients with active Clostridium difficile infection. Active infection is defined as a stool sample positive for Clostridium difficile toxin by EIA and either symptoms (frequent loose stools) OR imaging findings consistent with toxic megacolon. * Inability to take oral supplements * Patients with existing gastrointestinal symptoms including abdominal pain, diarrhea (watery stool), nausea and/or actively requiring regular anti-emetics. * Patients with symptomatic bowel metastasis including pain, severe constipation, or gastrointestinal bleeding. * Receiving antibiotic within 14 days of ICI therapy initiation. * Any physical or psychological condition that, in the opinion of the investigator, would pose unacceptable risk to the patient or raise concern that the patient would not comply with protocol procedures.