My grandmother practically a vegetarian, worked on a farm, up at 4am each day to bake bread, had 10 children. Walked everywhere and never sat around not in any way fat. She developed type II diabetes.

My Dad was overweight but active. Later in life after retirement sat around but still fished and like yard work and home repairs. His brothers and sisters had diabetes Dad never developed it.

I'm not denying poor lifestyle can be a cause then again it can seem to be a crap shoot.