Logging on to Facebook to see what your friends are doing may make you feel better about yourself, but it may also make you fatter, lower your credit score or trigger a round of binge eating.

Those are the surprising conclusions in a study in the Journal of Consumer Research, which found that participating in online social networks can have a negative effect on self-control.

“Using online social networks can have a positive effect on self-esteem and well-being. However, these increased feelings of self-worth can have a detrimental effect on behavior,” wrote authors Keith Wilcox, Columbia University and Andrew T. Stephen, University of Pittsburgh.

Wilcox and Stephen conducted a five part study of Facebook users. They found that although people on Facebook did experience an increase in self-esteem when involved with close friends, they also lost self-control once they were off Facebook and were more likely to choose an unhealthy snack as they browsed the internet.

“Because consumers care about the image they present to close friends, social network use enhances self-esteem in users who are focused on close friends while browsing their social network. This momentary increase in self-esteem leads them to display less self-control after browsing a social network,” the authors wrote.

In the study, hundreds of Facebook users were asked about their internet use, the closeness of their Facebook friends, and how much those friends’ opinions mattered to them. They were also asked questions about their finances, health, and offline social behavior.

In one phase of the study, participants were told to spend time browsing either Facebook or the CNN website, and then were asked if they wanted a cookie or a granola bar.

Others were asked to perform a mentally challenging task. After browsing either Facebook or CNN, they were given a series of difficult problems to see how long it would take before they gave up.

Greater Facebook use and a large circle of Facebook friends were associated with a higher body-mass index, increased binge eating, lower credit scores, and higher levels of credit card debt.

“These results are concerning given the increased time people spend  using social networks, as well as the worldwide proliferation of access  to social networks anywhere anytime via smartphones and other gadgets,” Wilcox and Stephen said.

“This is particularly true for adolescents and young adults who are the heaviest users of social networks and have grown up using social  networks as a normal part of their daily lives,” the authors conclude.