The prevalence of overweight and obesity has been high in most industrialized nations, since the early 1950s; however, this trend accelerated in the 1990s. Australia has not escaped this phenomenon . The risk of cardiovascular disease increases with overweight and obesity . According to the Australian National Health Survey conducted in 2001, 16% of men and 17% of women (aged more than 18) were obese, 42% of men and 25% of women were overweight, and 1% of men and 5% of women were underweight .
An extensive literature has been published on job stress and cardiovascular disease (CVD), mainly among men . This literature demonstrates that job strain and high effort/low reward conditions predict CVD [6–8], but the relative contributions of direct and indirect mechanisms remain unclear. Some evidence suggests indirect effects of psychosocial and other work conditions on health through health behaviours .
Indirect pathways may include effects of job stress on physical activity, eating behaviours, and other behaviours that may be related to BMI . Previous studies have found associations between working conditions and health behaviours, such as diet, physical activity and alcohol consumption, which impact weight change [10–12]. For example, in a cross-sectional analysis of Japanese workers (n = 6,759) job strain was associated with low vegetable and high alcohol consumption . Another cross-sectional survey of American workers (n = 3,843) showed that job demands were positively associated with high fat intake in men, while decision latitude was positively associated with physical activity in both men and women . More recently, the Helsinki Health Study (n = 6,243) found that among women, mentally strenuous work and high job control were associated with a healthy diet .
The two most widely used instruments to measure occupational stress are Karasek's demand/control (DC) and Siegrist's effort/reward imbalance (ERI) models. The demand/control model focuses on task-level job characteristics. It postulates that psychological strain results from the interaction of job demands and job control, with the combination of low control and high demands producing "job strain". In contrast, the effort/reward imbalance model includes personal characteristics of the worker (i.e., over commitment) and also conceptualizes and measures work conditions more broadly than the demand/control model. It focuses on the reciprocity of exchange at work where high costs/low gain conditions (i.e., high effort and low reward) are considered particularly stressful.
While the demand/control and effort/reward imbalance models have been tested in relation to CVD outcomes they have been less widely investigated in relation to risk factors for CVD including body mass index (BMI) . Nonetheless, fourteen studies have been conducted using job stress to test for associations with body mass index [4, 13–25]. The DC model was used in ten of these studies [12–16, 20, 21, 23–25], two of which also used the ERI model [13, 14].
Six of the studies with the DC model showed a positive and statistically significant relationship with BMI [12–15, 20, 24] but the remaining four showed no association. Both studies with the ERI model showed a positive and statistically significant relationship with BMI [13, 14]. And, two of the remaining four studies utilizing other measures of job strain showed positive and statistically significant relationships with BMI [4, 18].
In these positive investigations with the DC and ERI models, high job strain , low control [13, 24] and high ERI  have been linked with increased BMI. Among the four workplace studies of stress and obesity that did not use the DC or ERI models, the results varied [4, 22, 26, 27]. House et al. , using data from the Tecumseh Community Health Study from 1967 to 1969, demonstrated negative associations between occupational position and "pressures on the job" in relation to obesity for both men and women.
In a study of 1,137 Swedish women, Rosmond and Bjorntop  found that education, satisfaction with management, attempts to alter work situation" (i.e., a proxy measure of participation and control), and physical exercise were all negatively associated with BMI.
In a cohort study, Kornitzer and Kittel  found no association between job stress and obesity. The stress measure they used in this study of obesity was also tested in relation to coronary heart disease and was also non-predictive. Conversely, Georges et al.  found a borderline significant positive association (P= 0.06) between job demands and increased BMI. This survey also demonstrated that men with high job strain were more likely to have a pattern of central body fat distribution then men with low job strain .
Non-psychosocial working conditions have been investigated in relation to body mass index also. Using data from the National Population Health Survey in Canada, Shields  demonstrated that, after statistical adjustment, men who worked more than 35 hours a week had an odds ratio of 1.4 for being overweight (BMI> 25). No association between long hours of work and overweight was demonstrated for women.
Using a representative survey of workers in the Australian state of Victoria, we have assessed associations of job stress (i.e., demand/control; effort-reward imbalance models), shift work, physical demand and hours worked, with BMI among men and women.