I think a lot of it is going from fresh to processed foods and eating different types of foods.
Taiwan is a perfect example. It was pretty rare to see a fat person in Taiwan when I was growing up.
My mom would go down to the fresh market every day to buy vegatables, etc.
Now, I can tell that the overall weight of kids has increased vs. me when I was a kid.
Part of it is economy. Taiwan has become richer, so people can eat more food. Years ago, people had just enough to eat to survive. Not much extra.
So, I guess it is a combination of things.