Nutrition has come a long way since I started running marathons in the 80’s.
I think we always knew that being hydrated was good, however since the move to fructose and caffeine in drinks, plus gels that taste ok, plus recovery drinks that work the normal athlete can go further and faster for longer, if they get the nutrition right. Not only that, they can recover quicker so the next days session is possible.
We work hard to get a nutrition plan that works for you, all athletes are different, but there are general principles that you can work to. The art, rather than the science is to get the best plan for you, through a bit of trial and error.