But you can definately be a FAT vegiterian, if you're not careful...
Anyone ever wonder why ALL the largest creatures that ever lived on earth are all 100% vegiterians? Brachiosarous, elphants, hippos, cape buffalo, giraffes, horses, bison, etc...
T-Rex was a big guy, but the plant-eating dinosaurs that were his contemporaries were MUCH larger...
Also notice that the closer a land-animal is to being 100% carnivore, that they are actually quite thin & sleek? Cats are about about the closest to a 100% meat eater, yet I've never seen a wild cat of any species that was anything but lean & mean...