While poor diet and lack of exercise are usually to blame for excessive weight gain, a new study from the Kaiser Permanante Center for Health Research discovered stress and sleep deprivation can also cause people to pack on the pounds.

The study, published in the Journal of Obesity, found people who are trying to lose at least 10 pounds were more likely to do so if they had lower stress levels and slept between six and eight hours a night. Nearly 500 overweight people from Oregon and Washington participated in the study.

Participants with the lowest stress levels who received more than six hours - but no more than eight hours - of sleep were twice as likely to shed at least 10 pounds compared to those who had either the highest stress levels or slept for less than six hours.

"Some people may just need to cut back on their schedules and get to bed earlier. Others may find that exercise can reduce stress and help them sleep," said Dr. Charles Elder, the lead author of the study.

A recent survey by the Centers for Disease Control and Prevention found that one third of Americans get less than seven hours of sleep, a problem that could lead to weight gain and other conditions that could affect health insurance rates. Moreover, sleep deprivation can boost stress levels, making it more difficult to lose weight.