Amongst some vegetarians their diet seems to be some sort of miracle dietary choice yet its not favoured?

It has made me think about some of the common statements made by most veg/vegans that they seem to think that their dietary choice is the most healthiest yet no dietitian nor medical profession guides their patients to choose vegetarian if they want the so called healthy life style that the veg/vegans claim. Is it proof that it is their own belief and not of any profession??