The myth that if you're "overweight" it's because you're lazy or eat too many processed foods is most easily proven bullshit when you see things like the "Venus of Willendorf" which is believed to be more than 28,000 years old.
I wasn't there, but I'm pretty sure there wasn't a lot of laying around on the couch and eating snack-cakes and sugar drinks in the year 25000 B.C.E.