I'm somewhat surprised at the responses I've heard people in this thread received from doctors. Most doctors I've known have always advocated diet and exercise as being the two key controllable factors in a persons health and weight. That is I've never heard one of them emphasize exercise alone, its always diet and exercise and failing that then at least improving the diet. The ways I've always heard them describe improving one's diet was less meat and more fresh fruits and vegetables. I'm shocked to hear doctors incredulous as to the powerful role diet plays in health - considering that is something that has been taught even in the most commercial of main-stream medicine for decades and born out consistently by literature. These don't just sound like doctors stuck in convention but doctors who aren't even familiar with convention let alone the less conventional.
That is not to say that my doctors and friends of mine who are doctors have not consistently expressed skepticism with regard to raw-food diets. They have, but when I explain things to them and they realize I've done my homework they confess that they're not skeptical about the potential of such a diet so much as they are of their average patient's attention to nutrition required or will to see it through without giving up. Given the other patients I see in the waiting rooms though, its hard to blame them too much for being becoming jaded and skeptical when many of them don't seem to be following the simplest changes they suggest.
Of course they did have concerns about vitamin b12 in such a diet; but as the owner of this site, Alissa, points out that is something that an informed raw-vegan should be careful of. My most recent doctor has explained that this issue is actually the source of what she apologized for as misplaced frustration and skepticism with discussing nutrition with some of her vegan patients. She eventually realized though that responding to her vegan patients who refused to listen regarding the B12 deficiency potential by closing down herself and refusing to work with their desire for a raw-vegan (or even just vegan) lifestyle was both hypocritical and unhelpful.