This study investigates the feasibility of a low-protein diet for patients with metastatic castrate-resistant prostate cancer (CRPC) who are receiving immunotherapy. Metastatic CRPC is a type of prostate cancer that has spread to other parts of the body and continues to grow despite treatments to lower testosterone levels. This study aims to understand if a low-protein diet can be safely and effectively implemented alongside existing treatment.

Participants in this study will follow a specific low-protein diet while receiving their usual cancer treatment. The study will monitor the effects of this diet on the participants' health and cancer progression. Participants will not receive any payment for their involvement.

• Who can participate: Men with metastatic prostate cancer confirmed by scans and tests, who have disease progression despite hormone treatment, may qualify. Participants must have adequate blood, kidney, and liver function. They should not have severe symptoms or require strong pain medication.
• Study details: Participants will follow a low-protein diet while receiving their standard cancer treatment. The study will compare their health outcomes with their previous health status. No payment will be provided to participants.