I don't trust wikipedia for everything, but it may give you a better idea about the different kinds of diets out there:
http://en.wikipedia.org/wiki/Raw_foodism
The thing that kills people by being vegetarian or vegan is the processed foods. Yeah they could be eating healthier but the processed foods is the tasty empty calories that are helping them gain the weight.
This was one of my reasons to go raw, I noticed that processed foods whether veggie or vegan were the prime source of why people were not able to maintain their health or achieve their goals. I knew that if I went veggie or vegan I would have too much temptation to eat processed foods among other reasons.
Anisha