The one that is documented is Vitamin C. Eric Verdin has shown that elevated insulin activates a gene complex that inhibits the bodyās endogenous defences against oxidation, and the β-hydroxybutyrate produced on a ketogenic diet deactivates those genes, thus restoring the bodyās endogenous anti-oxidant defences, and greatly reducing, if not eliminating, the need for exogenous anti-oxidants. So
β-hydroxybutyrate has epigenetic effects, as well as providing fuel.
Fresh meat has been known for centuries to prevent scurvy. The problem the British Navy faced was that it was impossible to stock enough livestock to provide their sailors with fresh meat on long deployments, so they settled on Vitamin C from lemons and limes, instead. It was simply much easier to stock citrus than to provide fresh meat. (Once the livestock were all eaten, the sailorsā diet became shipās biscuit and salted beef.)
But you are right that the rest of the speculation is not documented. However, physicians who treat low-carb/keto patients notice lower thyroid values, but no symptoms of hypothyroidism, so there is a growing body of case studies to show that the body may use thyroid hormones more efficiently, without insulin to interfere.