I am not here to oversell this way of eating, it is not a "miracle drug". It will not instantly make you faster, stronger, or improve your cardio simply overnight.
Actually, if you are not currently eating healthy you may have "toxic withdrawal" symptoms. This is withdrawal from the bad foods you have been eating. Once you change to this healthier diet you may actually feel tired and generally worse for possibly up to two months, depending on how bad your current diet is. But after this initial withdrawal time, you will notice your energy begin to increase. You will continue to gradually feel better over time and eventually you will feel better than you ever have in your life.
Depending on your current cardiovascular situation it could take a few months up to three years to get your cardiovascular system where it is functioning at a 100% optimal rate, although you will see improvements fairly quickly. Three years would be an extreme case where someone who has significant plaque buildup and blockages of their arteries of 50% or more.(I base this estimate on my own personal experience, see the "About" page on this website).
So while my recommendations will not be an overnight miracle. I will guarantee that you will see significant improvements in your cardiovascular system(unless you at the utmost optimal now, if so it will allow you to maintain this optimal level for years to come), improved immunity, more energy, faster recovery times and overall long term general health and disease prevention(which is an area I think many athletes neglect).
My big question now is just how long could a professional athlete compete if they ate properly and wanted to compete. MMA fighter Randy Couture has proved you can go to 47 yrs. old even in what most consider a young mans sport.
So how long could someone compete in other sports? I really don't think we have seen the possible potential yet.