Wow this has turned out to be an ultra informative thread!!
Granted there are peeps with infinitely more knowledge than me on this subject; and just about every other
I still stand by my main point which is 'horses for courses.'
Do what feels best to you. What works for one may not work for the other, and vice versa.
John Fitch is a vegan, Nick Diaz smokes weed, Jeff Monson eats bacon but not bread before a fight, Usain Bolt eats Mcdonalds before a race and Luke Cummo fasts before he fights. Now these are all successful athletes we would be looking to emulate, right? But doing all of this would be massively contradictory.
Also dont underestimate the power that the mind plays in all of this. The placebo effect and the effect of positive thought can override a lot of what we deem scientific fact. All the studies in the world will still leave us without many of the answers. As humans we love to be problem solvers but there's a lot we will never truly understand. To try to get to the bottom of it all is absolutely futile. You are far better off finding what makes you feel good and sticking with that, if you feel good your body will run smoother, that should be obvious and explain why we do things that make us feel good.
For me personally a healthy balanced diet is important to performance, but not as important as confidence. Confidence is the biggest performance enhancer I personally have experienced. Whether I take vitamin c, d and any other letters of the alphabet wont help me train harder if I am not in the mood to train. A big part of the game is mental and thats something that there really is no one rule for all.
Lastly whenever giving advice I always air on the side of caution. Its one thing finding what works for you, 1200 mg of vit c may have made a massive positive difference to a persons training for example, but to assume that thats gonna be the answer to every athletes needs is missing the point. Ive been advised a lot based on what works for other people. Yes it has worked for them, I am not questioning that, but they are not me. So only I can say what works for me.