The study, recently published in the Journal of Consumer Research, found that the users who interacted online with close friends had higher body-mass indexes, were more likely to binge eat and had more credit-card debt.

In an attempt to understand how our online interactions affect offline decisions, researchers conducted five experiments on over 1,000 Facebook users.

In the first, participants completed surveys about how closely connected they were to their Facebook friends.

Those who did not have close friends on the site did not experience any change to their self-esteem while browsing or writing about the site, while those who did have close friends, experienced enhanced self-esteem after browsing.

The second study sought to understand the effect on self-esteem for those with close connections. Divided into two groups, the first was asked to browse the site and focus on information that was being shared with them, such as friends' status updates. The second group focused on the information they shared with their friends. It was found that those who focused on their own sharing experienced increased self-esteem.

"We find that people experience greater self-esteem when they focus on the image they are presenting to strong ties in their social networks," said co-author, Professor Keith Wilcox. "This suggests that even though people are sharing the same positive information with strong ties and weak ties on social networks, they feel better about themselves when the information is received by strong ties than by weak ties."

The final experiments involved browsing on either Facebook or CNN.com and then choosing between either a cookie or a granola bar and bidding in an auction.

The researchers found that Facebook users who focused on people they considered close friends were more likely to choose the cookie over those who didn't focus on close friends or those who browsed CNN.

In the case of the online auction, users who focused more on close friends while browsing Facebook again displayed less self-control, making higher bids than their counterparts.

Bringing the final experiments full circle was the finding that when users browsed Facebook and were told to share information with close friends instead of distant connections, they reported levels of higher self-esteem after browsing.

"People try to put their best faces forward on social networks and browsing... [which] can enhance users' self-esteem and make them feel better about themselves," Wilcox said. "The downside is that it results in an overinflated ego and manifests itself in negative behaviours."

It's not all bad news for those with real, genuine Facebook friends. "Social network use can help people feel better about themselves, enhance their social capital, and help them build relationships," Wilcox said. "The more people are aware of these negative tendencies, the more likely they are to counteract them."