Using social networking sites like Facebook can lower self-control in people who have many close friends on the site, according to a new study. Low self-control is linked to overeating and going on spending spree.

Researchers say that using Facebook to interact with family and friends can boost self-esteem, which is a good thing. However, excessive use can lead people to lose self-control, causing behavioral problems.

"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. 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," write authors Keith Wilcox (Columbia University) and Andrew T. Stephen (University of Pittsburgh).

Facebook has a billion users now and researchers have done many studies to find out what makes social networking sites so appealing. A recent study, from Harvard University, found that it is the "self disclosure" offered by these sites that lures in users to constantly update their profile pages. In other words, people love talking about themselves and these sites offer them a platform and an audience. Another study found that Facebook may be more tempting than sex or cigarettes.

Researchers found that people who focus on close friends while on Facebook are more likely to make unhealthy food choices after spending time updating their profiles due to enhanced self-esteem.

People who tend to overuse Facebook and have many close friends on the site were more likely to have high body-mass index, increased episodes of binge eating, higher levels of credit card debts and low credit card score.

The study results are disturbing, more so because social networking sites have proliferated in almost every country and many people are spending an unhealthy amount of time on these sites, researchers said.

"Given that self-control is important for maintaining social order and personal well-being, this subtle effect could have widespread impact. 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.

The study will be published in the Journal of Consumer Research: June 2013.