David Zabriskie rode the last Tour de France as a vegan:
http://www.independent.co.uk/news/world/americas/american-will-be-first-cyclist-to-ride-a-vegan-tour-de-france-2304496.html

There is quite a bit of online information about his diet. However . . . Macronutrients are divided into three classes: carbs, protein, and fat. We need a more-or-less specific number of grams of protein and fat each day. Carbs we vary according to energy use. So if protein and fat and carbs are in certain fixed proportions in the foods we eat, if we cut down our calories to normal human levels of say 3000 cal/day instead of the 10,000 that a Zabriskie may eat, we see that our protein and fat could easily be reduced below the levels necessary, if you see what I'm saying. So just eating what Zabriskie ate may not work at all for the average person.