I am vegetarian by birth. Although this question is not meant for me but i cannot resist myself answering this one, its my favorite topic . So i can give the answer in an alternate way, providing reasons to non vegans that may help them becoming a vegan.
Firstly we are designed as a herbivore. for more insight visit http://michaelbluejay.com/veg/natural.html. Its not a spam or an advertising website.
Secondly herbivore food has more energy content (approx. has 10 times more energy then non veg diets), can be easily explained by 10% law of energy transfer in trophic level, and are easy to digest so full utilization of the food.
Thirdly Plants are more appropriate choice morally as well because they have less senses, they only sense touch compared to 5 sense animals, they are static and so less sensed by us, also they are harvested in there last stage of life unlike animal which are slaughtered when they are young and flesh full. Trees are left as it is, we just go for the fruit.