Yes. The traditional Indian medicinal system called Ayurveda (as well as traditional Indian culture in general) regarded food as a form of medicine. Every form of food could potentially affect your body in various ways and many disorders and diseases were treated by either modifying the diet or by special herbal concoctions (as the concept of synthetic, molecular medicine wasn't discovered back then)... it makes sense for preventing many lifestyle related problems.

Possibly, but the problem is it's not rigorous.

If your doctor tells you to do 10 things, where 1 of them is the right move, 1 of them is dangerous, and 8 of them are placebos... then you don't really have a doctor.

Quite possibly ... not too long ago, knowing what you could and couldn't eat and the effects were surely part of oral tradition.

E.G. US natives knowledge of the pain-killing effects of 'something' in birchbark existed long before Bayer synthesized the same chemical in the late 1800s.

sample of one. Lactulose breath test confirmed SIBO with pretty high levels of both - hydrogen(78) and methane(29). Antibiotics didn't really work and resulted just in a minor improvement (depending on study, the antibiotics work in 30%-70% cases). The GE was very reluctant to prescribe even the second antibiotic, and lectured me on very low chances for success in the long term anyway as the issue tends to return soon even when antibiotics work ("we can't give you antibiotic every month, cant we?"). When the 2nd didn't work too, i didn't see a chance to make him prescribe the 3rd. So i went with traditional methods and medicines (interesting that the traditional way in addition to addressing direct manifestation - ie. bacterial overgrowth in this case - also focuses on root causes which wasn't the case with the GE). That worked (slowly, took few months), and the maintenance mode is far cry from the supposed monthly or whatever periodic begging of the GE for antibiotic (i didn't like his approach, yet i understand that being board certified he most probably has very good reason for his position/approach as, in particular, frequent use of antibiotics is known to be not a good thing).