Not sure if you are on any drugs. ADT drugs give many people bigger appetites, and they gain weight. This is a personal decision as other people have said. I weigh myself every day and base what I eat on what I weigh, It sounds like you are keeping the same diet, but losing weight

I have had a couple of times in the last five years when I lost five or 10 pounds, Over a couple of months and could not gain it back without eating significantly more. I’ve had PC for 15 years but those were the only times.

Just having prostate cancer, doesn’t normally cause weight loss, right away. It would normally take a long time for your system, to be degraded to the point that that would happen. Of course, if you had a Gleason Nine or 10 and a high decipher score your cancer had spread a lot…….But you don’t give us a clue about that.