Are you struggling to lose weight? The reason for that extra padding might have less to do with diet and exercise and more to do with your car.

A new study from researchers at Australian Catholic University found that people who spend an hour or more a day in a car are heavier and have larger waistlines than those who spend less than 15 minutes behind the wheel. The research team, led by professor Takemi Sugiyama from the university’s Institute of Health and Ageing, compared the driving habits of 2,800 adults from the Australian Diabetes, Obesity and Lifestyle Study with information about each participant's health such as weight, waist circumference, body mass index (BMI), fasting glucose levels and other metabolic factors.

According to the study, participants who spent more than an hour a day in their cars tended to be five pounds heavier and have waist measurements more than half an inch larger than their peers who spent 15 minutes or less in the car each day. Heavy car users also had BMIs around 0.8 greater than their peers. The study also found the correlation was greater for men than for women.

In Australia, where the study was conducted, 78 percent of adults admitted their car was their primary method of transport. In the U.S., that number is more like 86 percent. It's no wonder then, that American waistlines have grown by an inch over the last decade.

Sugiyama says he hopes this study will add to the growing body of research about the negative effects of relying on cars as a primary means of travel. He would like to work with researchers in environmental and transportation planning agencies to show how cars not only add to pollution and climate change, but they also have negative consequences for human health. He is hoping this study will convince people to get out of their cars and utilize more active forms of travel — like walking and cycling — not just for exercise but as a means of getting around and to promote better health.