The Most & Least Healthy or Obese Jobs: Graphic.
Obesity by Occupation: In the US police, firefighters, and security guards lead the pack. (Via wsj.com)
Exercise is only one factor. Eating and sleeping patterns (which might be adversely affected by a night job) are huge.
Note: this BMI stuff is imperfect at best: “Actually generally speaking, pro athletes tend to carry a lot of muscle and thus weigh more than the average person per a given height, so by BMI standards, many will appear to be obese. I’d venture to guess that a majority of NFL and NHL players have a BMI greater than 25 …Rugby players average a BMI of around 32, which means that over 50% of rugby players are obese.” But while BMI is flawed when looking at an individual, when looking at a large group of people, as this study is, it tends to be reasonably accurate.