Comment by Jweb_Guru

"Less healthy" is distinct from "shortens lifespan" which was pretty much the entire point I was making.

I understand that the idea that there are well-controlled massive studies with enough power to detect differences from weight alone is appealing, but they simply aren't there -- which should tell you that even if the effect exists, it's not strong enough that it should be your primary motivation to lose weight. There are already plenty of reasons to lose weight that don't require lying to people about having a BMI > 20 shortening your lifespan.