Joseph:
There is an obscure Ramban that discusses the subject of medical care by a professional. He essentially states that there is a science that utilizes empirical study that must be the training of anyone practicing in the field. No, he doesn’t endorse a particular medical school. But he states clearly that those who lack this scientific training should not engage in the practice. The context of this is a discussion about the mishna that exempts a physician from liability if a patient was injured or harmed in the process of healing. The message is that “The surgery was successful, but the patient died” is adequate to free the doctor of liability. But this is limited to the physician who is trained and expert. The charlatan or untrained doctor (lacking the empirical background) is liable for any harm.
I have personally witnessed adverse reactions to vitamins and supplements recommended by “experts” in that field. B”H none were life threatening. I have also observed some of the advocates of this approach bombard family members of someone with the dreaded illness, looking to stop chemotherapy and traditional medical care for IV drips of various vitamins. The fight was between these advocates and oncologists with years of experience. It was sad to watch patients die because their families withheld responsible treatment.
There is a place for nutrition management, supplementation, etc. The federal government requires labeling that specifies that these products cannot be used to diagnose or treat any medical ailment (check the labels for exact wording). The advocates would override that. Results are typically tragic.