Could your job be making you obese?

The new study, by researchers at the University of Adelaide, Central Queensland University and the University of South Australia, shows that having skills and the freedom to use them at work is linked to lower BMI and smaller waist size, whereas needing to make a lot of decisions is linked to bigger waist size.

The findings suggest for the first time that these two psychological measures of control at work may actually have very different effects on our waistlines, so should be assessed separately.

Control in your job can come in two broad forms: skill discretion -- having and being able to apply skills -- and decision authority. Traditionally, increasing an employee's level of job control has been seen as a good thing and the two factors have been considered together when looking at their effect on people's health. However, the new study suggests that the two aspects of job control should be considered separately in terms of their effects on health, and obesity in particular.

In 2014, more than 1.9 billion adults worldwide were overweight; of these, more than 600 million were obese. One area of interest for researchers has been how the kinds of work people do, and their experience of their work, can contribute to obesity.

"Many people point to 'eating too much and not moving enough' as the cause of obesity," said lead author Mr. Christopher Bean, a health psychology PhD candidate from the University of Adelaide. "While this might explain how weight gain often happens, it does not acknowledge things such as environmental, psychological, social or cultural factors -- these are some of the important why reasons that obesity happens."

For the study, which was part of the North West Adelaide Health Study, Bean and colleagues looked at a sub-set of data from 450 mostly middle-aged participants (230 women, 220 men), who worked in a variety of different occupations, both blue and white-collar. They measured participants' height, weight and waist circumference in a clinic and conducted telephone interviews to collect information about their work. They used a model called the Job Demand-Control-Support (JDCS) model to assess the psychosocial qualities of their work.

Traditionally, high job demands are considered stressful, while high job control has been considered useful in mitigating the effects of high demands. However, skill discretion and decision authority are usually assessed together. In the new study, the team took these two factors separately. After controlling for sex, age, household income, work hours and job nature, these two factors were comparatively strongly associated with obesity, with surprisingly opposite effects.

"When looking at the wide system of factors that cause and maintain obesity, work stress is just a small part of a very large and tangled network of interactive factors," said Mr. Bean. "On the other hand, work is a fundamental part of life for many, so it is important to find innovative ways of extending our understanding of how factors at work may be implicated in the development and maintenance of obesity. It is important to challenge the status quo and explore unexpected or counter-intuitive findings with curiosity."