Many policies and reforms can be enacted to fix obesity in America. For example, you can tax junk food at a higher rate in order to discourage their consumption. You can force manufactures to make healthier products by banning substances which cause obesity. You can also provide commercials and advertisements on TV to exercise and eat healthier.
Government agencies and policy have limited intrusion into private behavior, which is as it should be. Obesity is a personal problem and a medical one, and while the government may be able to influence some people to eat healthier and exercise more, particularly children, a real change in obesity rates will only come with social and individual lifestyle change.