This is not true. It isn’t any prove that people that weigh more than the “healthy” range are less healthy. That is just more stigma against fat people. Obesity as a concept is deeply intervowen with stigma.

I can recommend the podcast “Maintenance Phase”, where the hosts tackle these misconceptions and the stigma with deep dives into the actual research. Most of the debate about health is just bullshit and more about normativity and power than it is about health.