People stopped being poor. It's difficult to become obese when you simply don't have enough food. The solution to the problem isn't going to be in the past, because we want people to live a better life and not worse.

I think what will solve the obesity problem is education. The basic ideas of nutrition (in terms of physics and biology) should be taught to everyone. It should not be possible for someone to graduate high school and find the basics of a nutritional label difficult to understand.

This should also be coupled with a better cultural attitude. People should feel encouraged to try to lose weight when they're obese, rather than told some form of "healthy at every size" nonsense or be made fun of when they are at the gym. It should be seen as an ailment that can be improved rather than something shameful. If you have a broken arm, then you're not told that it's fine to have a broken arm, nor are you made fun of for trying to get your broken arm fixed.

I used to be overweight and I understood that it was bad, but it was difficult to try to improve it. The people around you notice that you're doing things differently and you'll hear snide remarks or encouragement, but this leads to expectations, so you try to hide it instead. That way nobody expects anything.