Need a quick ego boost? Spend five minutes on Facebook. But beware—it could also lower your self-control.

Researchers from the University of  Pittsburgh and Columbia Business School found that just five minutes on Facebook increased users’ self-esteem when they focused on what they shared with close friends (their own status updates or photos). But time spent on the social networking site also made users more apt to reach for a cookie than a granola bar—an apparent sign of weakened willpower—according to a report published in the Journal of Consumer Research.

Five separate studies were conducted with more than 1,000 U.S. Facebook users.

The first found that those with close ties to Facebook friends reported an increase in self-esteem while those with weaker ties didn’t. A second study evaluated why Facebook users with stronger friendships experienced that self-esteem boost and found it has to do with the way we want to present ourselves to close friends online. A third study saw participants reach for chocolate chip cookies over granola bars after spending time on Facebook, compared to those who read CNN.com. A fourth study found that users were more likely to give up on solving anagram word puzzles after logging on to Facebook as opposed to skimming TMZ.com.

The final study examined the relationship between online social network use and offline behaviors and found heavier Facebook use was associated with higher body-mass index, increased binge eating, a lower credit score and higher levels of credit card debt.

Social networking addicts don’t despair just yet. A recent study at the University of South Carolina’s School of Public Health found that Twitter could actually help you lose weight. Researchers found that dieters were more successful at shedding pounds when they received tweets of support or read inspirational messages via the microblogging site.

(Photo by Marcus Quigmire via Wikimedia Commons)