Obesity may be contagious -- because most people feel good about themselves if they are about as heavy as the people around them, according to new research.

This could explain the rapid rise in obesity around the world. The norm that most people compare themselves to has become fatter and fatter, feeding a cycle of "imitative obesity."

In the current analysis, researchers analyzed data from several sources on body mass index (BMI) and people's perception of their weight for 29 European countries. For women, satisfaction with their weight own depended on their BMI in relation to the average BMI for a woman of their own age living in the same country. Men who were overweight also tended to be happier if the people around them were overweight too.