Medicine 200 years from now will be different. Doctors are largely ignorant of nutrition. When you go to the doctor, how often do they ask about the what you eat? Unless you really look unhealthy or you mention some correlation between the symptoms and a specific food, your diet is a lowly weighted factor in your unwell being. I think that will change, and many of the catalysts will be from patients who teased out the effects of nutrition on what ails them.

There is also a significant leakage of nutritional advise from sports science, and all this information is finding adherents/testers in the regular world and will eventually (after the pseudoscience is sorted out) have a corrective influence on medicine.

I think at some point Medical nutrition therapy (MNT) will be a lot more common and maybe even have specific practitioners, (like physical therapists) instead of being a doctor-nutritionist partnership. The practice will evolve and it will get standardised and taught to "specialists".