I've only heard that from raw foodists and kind of view it a little skeptically. I read everything I could about vegetarianism when I gave up meat in my 20s -- had to have arguments to shut up my ex husband who was extremely opposed. I was a happy lacto ovo vegetarian for about 12 years until I became gluten intolerant. Can't stick to it anymore, my absorption is too impaired.
I'm forced to conclude that there is no single dietary approach, some people have genetic predispositions to certain lifestyles, others have ethical and spiritual considerations and still others have allergies and intolerances they have to eat around. In the end you need to find what works for your own body and moral compass

It's bizarre that some people who eat extremely low to no carb/high fat have similar physical responses to those who go radically vegan.
However, trying to do something like feed a dog a vegetarian diet -- like I've heard some hard core vegans do -- is just plain stupid.