There were obese people before “processed foods”.
Wealth and access have long been factors for some.
Anyone watch 600 lb lives? These are the same people who would be fat in pre Boomer times, supercharged by modern foods.
It’s about eating too much
Plenty super fat people take in enough from sweet drinks alone to reach daily caloric needs
Some folks have higher metabolism which helps them but metabolism effect baring super high thyroid is a long process for effect
It still comes back don’t eat double or triple daily weight maintain need
Somebody eats 7000 calories of quinoa they will still get fat
Folks esp lower income just don’t care as much anymore and often are less active than before