I don't think one needs to take it so literally.
"What nature intended" in this context is just another way of saying "optimal given the history of how humans evolved"
"What nature intended" in this context is just another way of saying "optimal given the history of how humans evolved"
The premise that there is something optimal about the state we evolved in has no basis in what we understand about evolutionary processes. Those are just the conditions that we happened to not die in, not the conditions that are in any way "best" or "optimal" for us. It's like sleeping in late and missing a flight that ends up crashing and assuming that the optimal strategy is to always sleep in late.
Further, in an ever changing environment, which is what make evolution so important, "history" in a genetic sense is completely uninteresting. Things that cause one species to not die in one era can easily be the source of it's extinction in a future one. Megafauna probably had many benefits, pre-human existence, from being very large. But being large and reproducing slowly is what ultimately let to their extinction once the environment changed.
Now there are undoubtedly environments that are better for humans than the Paleolithic one. However, it's hard to say for sure what they are specifically. Every chemical that enters your body has some effect, and if your body was never optimized to handle it, it may have negative effects, even if on the surface it seems better. Trans fats are a great example of this. If we had been eating them for 10,000 years, our bodies would have adapted to make them non-harmful.
Nobody said that.
> Things that cause one species to not die in one era can easily be the source of it's extinction in a future one.
That's exactly why the history is useful. We carry a long long list of traits, many of which wouldn't be there based on the recent environment, and may actually be counterproductive in it. And all of those are important to know about.