You can be an endurance athlete. And you can do it on a plant-based diet alone. And for everyone who worries about "not enough protein" concerns, there is not a "protein deficiency" going around. It's been estimated that everyone eats far too much protein as it is.

I highly recommend "Appetite for Reduction", by Isa Chandra Moskowitz. It's a low-cal, low-fat, but NOT low-flavor vegan cookbook. She heavily supplements with veggies, and all of the recipes are fantastic. I have nothing to gain by recommending this cookbook, it's just one that's my favorite and has helped me lose a bit of weight.

No matter what route you choose, good luck to you!