UCSF has some dietary guidelines for patients with prostate cancer. https://www.ucsfhealth.org/health-articles/nutrition-and-prostate-cancer
These don't necessarily apply during radiation treatment as the goal there is to minimize bladder and bowel activity that causes prostate movement during the brief time the radiation is administered.

I've been most interested in what I can do to counter the side effects of ADT.

There is a guy in Australia, Dr. Rob Newton, whose prime interest is how to use exercise as a first line treatment for prostate cancer. He is recognized as one of the leading exercise oncology researchers in the world. He claims the exercise programs his clinic develops for each individual patient that they treat has shown him that exercise can counteract "all" the side effects of ADT.

However, he seems reluctant to publish a general recommendation for patients who regarded themselves as in generally good physical condition prior to their PCa diagnosis. He appears most interested in studying advanced cases where unless he can intervene successfully, the patient will die. He watched his own father die of advanced prostate cancer after his father faithfully followed the then widely recommended prescription for prostate cancer which was to avoid physical activity and rest. This caused him to change his career path from being a top level physio coach for pro athletes, to prostate cancer research.

There is a PCRI video of a Newton detailed presentation of an overview of his research.

A section of the video that is possibly of more interest to someone looking for what to do as they are about to start on ADT starts around minute 45, after Newton opens up the floor to questions. Dr. Mark Moyad, after some crude exchanges because he and Newton are colleagues and old friends, puts Newton on the spot asking for more generally applicable info.

Exercise is gaining more attention as a first line treatment for PCa. The phase 3 CHALLENGE trial was significant enough that it was presented at a plenary session at the largest oncology conference in the world, ASCO 2025. It made it into the New England Journal of Medicine as well. It is the first randomized trial to prove that a structured, long-term exercise program significantly improves survival in patients with stage II-III colon cancer. Exercise reduced the risk of cancer recurrence or death by 28%.

ADT vrs no ADT does not improve patient outlook by that much.

Newton, with Kendricks of UCSF, et.al. has a multi center study going that looks identical to this, except the patients studied all have advanced prostate cancer. This is the INTERVAL-GAP4 Study, entitled "Intense Exercise for Survival among Men with Metastatic Castrate-Resistant Prostate Cancer". Trial Registration number: NCT02730338. My fairly local NCI designated cancer center was a location for this study, but they would not provide me with any info as to what exercises were prescribed or recommended, and at their location, the study is concluded.