A few years ago, I listened to a radio program (good ole radio 4) about body shapes and poverty over the years.
If we go back far enough, fat was associated with having lots of money ... enough money to eat what you want and sit around whilst the thinner, poor people who could not afford to eat as much ran around (burning off any extra calories they may have been lucky enough to eat) serving the "ruling classes".
This has now turned around in many countries. Work has become less physical and cheap food has become more processed. So, poor people are more likely to be fatter. At the same time, people with more money are eating less processed food and have time for the gym, etc. so are thinner.
Sure, there are so huge generalisations there and I have summarised a 30 minute program into a few sentences but, hopefully, you get the point.
I realise the relationship between weight a diabetes is not a simple one but I am sure there is something around cheaper more processed food, less physical activity, increased weight, poverty and diabetes.