Just shortly, because I am really not an expert on this, so debating longly feels inappropriate (it feels like suggesting that I know more than I actually do).

What explains why people are more obese than 50 years ago?

I still feel like there are at least two explanations here. Maybe it is more food and less hard work, in general. Or maybe it is something in the food that screws up many (but not all) people's metabolism.

Like, maybe some food additive that we use because it improves the taste, also has an unknown side effect of telling people's bodies to prioritize storing energy in fat cells over delivering it to muscles. And if the food additive is only added to some type of foods, or affects only people with certain genes, that might hypothetically explain why some people get fat and some don't.

Now, I am probably not the first person to think about this -- if it is about lifestyle, then perhaps we should see clear connection between obesity and profession. To put it bluntly, are people working in offices more fat than people doing hard physical work? I admit I never actually paid attention to this.