Dear Danny,
I was unusually fatigued for a couple of months after donating, I was back to my workouts pretty fast, but added time and intensity slowly. I was especially cautious with stressing the abdomen for a while. But now I never think about that at all!
Make sure to get some extra sleep. In the first weeks after donation, I slept a lot (over 12 hours a day!) and never did go back to less than 8 or 9.
I don't believe that eating huge amounts of protein will make you stronger or healthier whether you are a donor or not. I'm sure the nephrologist is not suggesting eating too little protein, but suggesting not overeating protein. I've never eaten a high protein diet, yet I had the endurance to run a couple of marathons, and the strength to bring home a couple of powerlifting trophies.
Love, elephant