Specific Groups at Risk

Anyone with Sedentary Lifestyles. Office workers, drivers, and anyone whose lifestyle involves sitting for long periods are at higher risk for obesity.

Ex-Smokers. The trend toward weight increase has followed the trend for quitting smoking. Nicotine increases the metabolic rate, and quitting, even without eating more, can cause weight gain, which may be considerable. It is important to note that weight control is not a valid reason to smoke. People in previous centuries did not smoke cigarettes, nor were they usually obese.
Shift-Workers. A recent study found that individuals who work late shifts (between 4 p.m. and 8 a.m.) tend to eat more and take longer naps than day workers and are more likely to gain excess weight.
People with Disabilities. Obesity rates are higher than average in people with physical or mental disabilities. Those with disabilities in the lower part of the body, such as the legs, are at highest risk.

http://health.nytimes.com/health/guides/specialtopic/weight-management/risk-factors.html