I don’t know if any of this can ever be proven since we can’t take a group of people and lock them up for a period of years. Hopefully someday we’ll have proof other than anecdotal evidence from people like me.
It turns out that weight loss may not be the only way that switching to metabolizing ketones from sugars may suppress disease. Ketones apparently have important physiological roles of their own; they “regulate the expression and activity of many proteins and molecules that are known to influence health and aging.” These include proteins and molecules involved in inflammation, cardiovascular and brain function, and glucose utilization. The NEJM review does not discuss any possible harms from high ketone levels and for the most part, these do not seem to be clinically significant for most individuals.Psychology Today