"Norman Garrick and Wesley Marshall have found that people in dense cities are thinner and generally healthier than people in sprawling subdivisions.
They looked at the three fundamental measures of street networks–density, connectivity, and configuration–in 24 California cities, and compared them with various maladies. In the current Journal of Transport and Health, Garrick and Marshall report that cities with more compact street networks—specifically, increased intersection density—have lower levels of obesity, diabetes, high blood pressure, and heart disease. The more intersections, the healthier the humans."
I think it has to do with car culture. Vancouver's west end has western Canada's highest population density. People walk a lot. Vehicle travel and parking are impractical for many. They are a fit bunch.
Surrey, on outlying suburb, has a more chubby population. Surrey is so spread out that it's not practical to walk to most places. Kids are driven to school and adults drive to work, shopping etc.
Go for a walk and you may not encounter any business that sells unhealthy food. Drive through Surrey, and you'll pass many. People don't decide to go for a brisk walk to Mc Pukes. They take the car.
edit --- Later that day --- I read the article. They didn't go with the junk food angle, but cars and commuting are discussed. I know a few people who commute long distances. They are too tired at the end of the day for any exercise. I don't often go on long drives, but when I do, I pig down chocolate bars and other snacky foods that I might not have eaten otherwise. I'm sitting in a comfy chair. Seems like a good reason to gorge on something.
Acetylsalicylic acid is aspirin. This could be handy too: