I was on the Discovery Health site today looking for an old special they aired about how obesity affects a body. It was called "My Big Fat Body" and starred Frank Payne. I wasn't able to find that video, but did stumble upon a theory about weight and gas prices. He theorized in his doctoral dissertation that every $1 increase in gas prices will lower obesity rates by as much as 9 percent after seven years, while saving 11,000 lives and $11 billion annually.
His theory is that higher gas prices lead people to find ways to save gas. This means finding other ways to get places than driving. Walking, cycling and public transportation become primary modes of transportation in an effort to save money. This leads to more fitness and calories burned. Secondly, because of the increased amount of money spent on gas, people eat out less, which means fewer calories consumed.
Comparing the maps of public transportation use to the one showing obesity seems to support his theory. The lighter blue states tend to be darker green. That doesn't prove causation, but does show some correlation.
Gas prices are currently rising pretty quickly, which is bad for our pocketbooks, but may not be bad for our waists. If you want to test out his theory, try to limit the amount you drive your car and dine out. Put the saved money into a jar and buy yourself some new clothes. It turns out that not driving may be really good for you.