@Soulfox -- Following the advice of a doctor is always best but don't think it automatically discounts the effectiveness of a diet. There are a lot of people who swear by various diets, so visiting with some of them may be a good thing for you to do. Ask them if they got ill when on the diet, if the lost pounds came off, etc.
If someone has a positive report on a diet, report those findings to your doctor and see if that doc can confirm or dispute them. Getting the most information you can is the best course of action when it comes to such things.