Hate to point out the obvious, but the true problem is Americans being too fucking lazy to maintain their health through diet and exercise. If they simply did this, there would be no reason to be demanding magical pills to fix a preventable problem.
The way I see it, there are three major contributors:
1) The majority of new development in the US is centered around the automobile. We collectively spend way more time in our cars and our air-conditioned homes and office buildings than ever before. The best way to get people to exercise more is to make it easy and pleasant. Make cities more walkable, create green spaces, make neighborhoods more neighborhood-like (ie: less suburban sprawl and more local amenities and services). Do your kids walk/ride bikes to school, or do you drive them? It is no coincidence that older cities like New York, Boston, DC, etc have better stats with respect to obesity and diabetes occurrence.
2) Childhood obesity. We learn our primary eating habits as children. Whatever you can do to encourage healthy eating for children, whether that be cooking lessons, less junk food, cucumbers and tomatoes instead of mac n' cheese for breakfast, is improvement. The problem is, if you are addicted to fast food, soda, and cheetos before you are 15 years old, it is really hard to change those habits when it starts catching up to you.
3) Time to cook/eat proper meals. True fact: not everybody likes to cook and will do that. But, if you can reliably work a 40-hour week, you might actually be able to spend some time eating properly, rather than grabbing the high-salt high-carb heavily processed food so you can quickly eat and run. If you cook your own meals it is cheaper and healthier for you in the long run, but you don't have to cook to be healthy. You just need healthy options available and affordable, but that requires time.