I second the research. Read, read, read and when you're done, read more. Be careful of your sources. Medical journals are the best place to start, if they are credible. If people give you random info, you can do one of two things. Either thank them and check up on it yourself, or ask them where they learned it and to back it up with facts and references. Most people cannot back up their opinions with concrete facts.
Even when studies are cited, that still may not guarantee what they are saying it true. There are actually factors that make studies valid. That's why (most) medical journals are a good place to start because the studies are often peer reviewed. My husband, who just finished his masters for Physician Assistant actually had a class on how to read studies, and determine their accuracy.
Also, a medical professional's knowledge can be effected by how long they have been in the field, if they have kept up on new research and their experience. Case in point, I am an RN and I learned that taking large doses of Vit C is a waste of money. Its a water soluble vitamin, so the more you take, you just pee it right out again. My husband did one of his research papers on the effects of Vit C on immunity and so far the research available still does not support or dismiss this age old idea. So the jury is still out on it, I guess. I've been a nurse for 5 years, and just in that time, maybe this diabetes effect has started to be researched, but I've never heard of it (and I would really ask someone to give some literature to back it up) BUT, its possible that I simple have not heard of this study and that its true. And it was not being taught when I was in nursing school.
Sometimes, some issues don't have a definitive answer, so different doctors will have different opinions. That's another factor.
If you are really tired of getting unsolicited medical advice from people, I would tell them that when they can provide credible proof, you'd be happy to listen. Or if they can explain the science behind why their advice might work, then that would be something you's be willing to try. Other wise, they can pedal it else where. You'll weed out the people that are just regurgitating what they heard someone else say, and that person they got it from heard it from someone else, and so on and so on. And you'll identify the people that actually have an interesting new piece of research or info to bring to the table and you may find some good advice.
While doctors don't know everything, they are far less likely to just spew wrong and unfounded info at you. Or to give a piece of advice they got from some random person. They do have a license to think about (as well as nurses) while lay people can give you the most inaccurate, dangerous advice and they have nothing to lose if they don't bother looking it up to make sure its true. That's something to think about too!
Hope this helps.