Well, almost everyone I've known since moving back to MA is a lot heavier. That's over 22 years, from ages late 30s to late 50s/60-ish. Of course, this doesn't count the people i know from riding, but I didn't know them in 1990. An astonishing number of them (particularly the men) have huge guts. And these people are super strong riders. Not so much the women. Funny, everyone i've reconnected with from my childhood is thin. And my friends in AZ, well, they are the same. The heavy ones are heavy and the thin ones are still thin.
I do believe that living in a city keeps you thin. Every vacation I've ever taken that involves a lot of city walking and a lot of eating has been a test of this factor. I never gain weight on these trips.