How is food different today?
I’m not arguing with that point. The problem is that we don’t know what about the environment is different today than from America in the 1920s to make a different.
A theory that I got from a commenter while back is that food tastes a lot better today. In the 1920s, besides being more expensive, food just didn’t taste that good, so people weren’t tempted to overeat.
Our bodies just aren’t adapted to plentiful (more than you can possibly eat) food that tastes way better than the food our caveman ancestors used to eat. On the other hand, people are living longer than they ever did in the past, so despite people worrying about diabetes and other ill effects of being fatter than in the past, there’s no hard evidence that we are worse off because of it.
And perhaps abundant food is behind rising IQs. More nourishment makes the brain grow better.