I agree with the last two posts. Until there's strong evidence and a medical consensus about a causal relationship between any kind of diet and prostate-cancer progression, your best bet is to continue to eat what would constitute a healthy diet if you *didn't* have cancer.

That can vary depending on your beliefs, culture, and other medical conditions (like allergies, high cholesterol or diabetes), but essentially, your grandma had the right idea: cover 1/2 of your plate with vegetables, 1/4 with starches (rice, potatoes, etc), and 1/4 with a higher-protein source. Eat modest-sized 1940s portions, not super-sized 2020s portions (buy smaller plates if it helps). Don't eat the same thing every day — especially not red meat, which your grandma probably couldn't afford to eat every day anyway.

As they reportedly say in the U.S. military, K.I.S.S.