Participants will be asked to pick up the fermented foods at the Research Kitchen at Moffitt. Participants will be asked to eat 3-6 servings of FFs per day, from 1 week prior to treatment start through 12 weeks after treatment start/until the restaging scope is completed.

At baseline, the end of week 6.5 and again at week 12.5, participants will be asked to provide biospecimens including a stool sample collected at home and a blood specimen collected in clinic.

Participants will be asked to complete a food frequency questionnaire, a quality-of-life survey, two symptom related surveys, and a stool collection questionnaire at these same timepoints.

After the dietary intervention, participants will be asked to complete an exit survey to provide feedback on the study and intervention.

Participants will receive general healthy eating handouts similar to current usual care documents provided in clinic.

These handouts will detail typical healthy foods and the suggested level of intake, or servings per day.

At baseline, the end of week 6.5 and again at week 12.5, participants will be asked to provide biospecimens including a stool sample collected at home and a blood specimen collected in clinic. Participants will be asked to complete a food frequency questionnaire, a quality-of-life survey, two symptom related surveys, and a stool collection questionnaire at these same timepoints.

3-6 servings of any combination of the following fermented foods/day (from 1 week prior to treatment to approximately 12 weeks after the start of treatment): Yogurt, cottage cheese, kefir, kombucha, sauerkraut, and kimchi.

Clinical response measured in clinic by MRI/Endoscopy/Digital rectal exam, comparing the FEED-FF arm to SUC arm.

Indicators of clinical response are Complete Response, Near Complete Response, Incomplete Response, or Progressive Disease.

Clinical benefit to immune checkpoint inhibitor therapy will be measured in clinic by MRI/Endoscopy, comparing the FEED-FF arm to SUC arm.

Defined as the best response of complete tumor resolution (CR), Partial Response (PR), and stable tumor size (SD) within 12 months.

Progressive Disease (PD) within 12 months indicates no clinical benefit.

Measured by fecal biospecimen sample collection; FEED-FF arm hypothesized to demonstrate increases in short chain fatty acid (SCFA) producing bacteria and higher alpha diversity compared to SUC arm.

Measured by FFPE tissue slides; FEED-FF arm hypothesized to demonstrate enhanced immune response such as higher T-cell expression compared to SUC arm.

Measured by using the European Organization for the Research and Treatment of Cancer (EORTC) Quality of Life (QoL) Survey; FEED-FF arm hypothesized to demonstrate more favorable QoL compared to SUC arm.