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
The “gut biome” is currently suspected of playing a role in obesity. Obesity may not just be due to caloric intake, but how gut bacteria process it.
https://pmc.ncbi.nlm.nih.gov/articles/PMC5082693/
“A link between obesity and the gut microbiota was initially suggested based on studies in germ-free mice. These mice are raised in a sterile environment and have no microorganisms in their gut. Conventionally reared mice have a 40% higher body fat content and 47% higher gonadal fat content than germ-free mice even though they consume less food than their germ-free counterparts.”