Stressed and gaining weight? The stress -- and the exercise-slacking or chocolate-munching it breeds -- may actually not be the main culprit.

Despite the common belief that stress causes people to pack on weight by reaching for junk food or avoiding exercise, on average it appears to have only small long-term impact at most, according to a study.

A review of 36 previously published studies on stress and weight gain led by Jane Wardle, at University College London, found that the majority showed no association between people's stress levels and their weight gain over several years.

When the study, which appeared in "Obesity," combined the results of the research, there was only a modest association overall between stress and weight gain. "We assumed that there would be a substantial association between stress and obesity, since the popular view is that stress contributes to weight gain," said Andrew Steptoe, who also took part in the study, in an email to Reuters Health.

"But when we looked carefully at well-controlled scientific studies, effects were surprisingly small."

The study analyzed 32 international studies conducted mainly in the 1990s and 2000s.

All assessed participants' stress levels, then followed the subjects over time to see whether there was a relationship between stress and subsequent weight gain.

Most followed participants for 1 to 7 years, but a few were longer term projects that followed people for up to 38 years. Some focused on work stress, while others covered general life stress -- anything from major traumas like a serious illness or a divorce, to feeling overwhelmed by daily issues.

Overall, 69 percent of the studies found no clear association between stress levels and weight gain, while 25 percent linked higher stress levels to greater weight gain.

The remaining 6 percent found that greater stress was related to less weight gain over time.

Once all the results were pooled, there was a modest association between higher stress levels and greater weight gain -- a connection stronger among men than among women.

Steptoe warned that while the impact of stress on weight may be small on average, there was the possibility of wide individual variations. The type of stress, whether work, caregiving or specific life events, might also have different effects on weight gain.

But measuring both was beyond the scope of the data they had.

"The general message is that, based on the best current scientific research, stress is not likely to play a major role in increasing body weight or obesity for most people," he said.

"It could be that some people are more affected than others, but rather little is known about this at present."