No, some chemical or chemicals got added to the environment around 1980.

All I can say is try losing 20 pounds and keeping it off for two years and how easy it is. Fat shaming might make a difference but I suspect it would be like knocking off 5 lbs from the average where you really need to knock off 50 lbs.

You only started seeing Victoria's Secret getting fat models in the last few years, the obesity epidemic on the other hand started in the Regan years. Maybe it's like taking your belt off when you get heartburn (though I know if I go that route pretty soon I'm going to need suspenders) Try

https://arxiv.org/abs/q-bio/0312011

for a theory that may be wrong but fits the chronology.