More than one-third of adults in America are obese, and doctors and dietitians have been trying to figure out what’s to blame — is it our diet, exercise, the way we sleep, or a combination of the three? According to a new study, published in the journal Social Science and Medicine, experts may have been missing something: the way we do our jobs. In a collaborative effort from several Australian institutions, researchers found employees with lower body mass index (BMI) were also more able to use their skills in the workplace.

"Many people point to 'eating too much and not moving enough' as the cause of obesity," said lead author Christopher Bean, a Ph.D. candidate in health psychology at the University of Adelaide, in a press release. "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 reasons why obesity happens."

The research team studied 230 women and 220 men who worked in a variety of occupations, ranging from blue- to white-collar. Their height, weight, and waist circumferences were measured at a clinic, and then interviews about their jobs were administered over the phone. The measurements were taken to get a fuller picture of their health. BMI, a standardized range used to classify a person as underweight, normal, overweight, or obese, has recently been criticized for its limitations because it’s a metric produced from a person’s height and weight. However, it doesn’t take into account muscle mass, which is heavier, and thus might misinterpret a muscular person as being overweight. Waist circumference, on the other hand, is a better indicator of obesity — and subsequent disease risk, too.

Next, they used the Job Demand-Control-Support (JDCS) model to measure the psychosocial qualities of participants’ jobs. They found that the type of control a person had over their job influenced their waistline. Specifically, people who reported skill discretion — having skills and the freedom to use them— more often tended to have smaller waistlines. Meanwhile, those who had control in the form of so-called “decision authority,” meaning they were trusted with making lots of decisions on a day-to-day basis, had the biggest waistlines.

Bean said research needs to start expanding beyond only the effects of exercise, sleep, and dieting when it comes to obesity. High job demands have also been shown to cause stress, which makes investigating workplace dynamics all the more important in determining how it ties into a higher risk of obesity. One example, possibly, is that the stress of making decisions influences what and how much people eat.

"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," Bean said. "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."

Source: Bean C, Winefield HR, Sargent C, and Hutchinson AD. Differential associations of job control components with both waist circumference and body mass index. Social Science & Medicine. 2015.