One striking thing to me, as someone who spends half my time in San Francisco and half elsewhere, is how much thinner San Franciscans are than most other Americans. Now, it could be because San Franciscans eat less sugar (perhaps because they are wealthier and eat better on the whole). But the Bay Area in general is pretty wealthy, and I think you still see a lot more large people on the peninsula than in SF. The peninsula is much more car dependent. I don't think it's a coincidence, but I can't prove it either.