I have read a lot of posts from people who said their doctors or nutritionists have not been positive about their veganism.
I've heard this, too. The thing is, both the (1) American Medical Association and the (2) Academy of Nutrition & Dietetics have stated that plant-based / veg diets are healthy (the Academy of Nutrition & Dietetics is the world's largest association of Registered Dietitians).
From the American Medical Association policy H-150.94 - Healthful Food Options in Health Care Facilities:
"1. Our AMA encourages healthful food options be available, at reasonable prices and easily accessible, on the premises of Health Care Facilities.
2. Our AMA hereby calls on all Health Care Facilities to improve the health of patients, staff, and visitors by: (a) providing a variety of healthy food,
including plant-based meals, and meals that are low in saturated and trans fat, sodium, and added sugars; (b) eliminating processed meats from menus; and (c) providing and promoting healthy beverages.
3. Our AMA hereby calls for Health Care Facility cafeterias and inpatient meal menus to publish nutrition information."
Link:
https://policysearch.ama-assn.org/policyfinder/detail/hospital food ?uri=/AMADoc/HOD.xml-0-627.xml
From the Academy of Nutrition and Dietetics' Position Paper on Vegetarian Diets:
"It is the position of the Academy of Nutrition and Dietetics that appropriately planned vegetarian, including vegan, diets are healthful, nutritionally adequate, and may provide health benefits for the prevention and treatment of certain diseases. These diets are appropriate for all stages of the life cycle, including pregnancy, lactation, infancy, childhood, adolescence, older adulthood, and for athletes."
Link:
https://www.ncbi.nlm.nih.gov/pubmed/27886704