I have considered adopting it, but I can't quite figure out how to get that to work with PT and marathon training. How do Catholic and Orthodox athletes do it?
"How do Catholic and Orthodox athletes do it?"
Lots of protein, which you can get from beans; lentils are great as are black beans and of course from fish. My oldest is a real jock, and he actually says he's in better shape during the fast than during the rest of the year.
I have considered adopting it, but I can't quite figure out how to get that to work with PT and marathon training
You can try several things. As in physical training, you should also pace yourself in spiritual training. Catholics give up meat on Fridays (this is not mandatory anymore, but still "suggested"). You could try something like this on days you don't train. Give up a particular food that you enjoy and eat something else that is more healthy.
And of course, food is not the only thing we can "fast" from. How about television? One could cut back on that as well. I find that the Lenten experience is a good means of developing one's willpower. If we can't give up meat one day a week, how are we going to resist the temptations that we come across all the time?
Regards