It's science, people: Spending a lot of time keeping up with your buddies on Facebook (FB) will weaken your self-control. It will expand both your waistline and your credit card bills. That's according to a new study, "Are Close Friends the Enemy? Online Social Networks, Self-Esteem, and Self-Control," that will appear in the June 2013 Journal of Consumer Research, which found a significant relationship between Facebook usage and individuals' self-control. There's no shortage of research attempting to mine all the positive and negative ways our use of social networks affect our attention spans, our brains, our behavior and our table manners. Just a couple of examples: UK scientists found a direct link between the number of friends a person has on Facebook and the size of their brain regions. A separate study by a psychology professor at California State University, Dominguez Hills, found that teens who use Facebook more often show more narcissistic tendencies, while young adults who have a strong Facebook presence show more signs of other psychological disorders, including antisocial behaviors, mania and aggressive tendencies.. Studies have also found differing effects of high Facebook usage on self-esteem. In the Journal of Consumer Research paper, the authors argue that using online social networks like Facebook lifts self-esteem, particularly for those users focused on their close friends while browsing the site (i.e., not your classmate from high school you haven't spoken to in 12 years). "It really only happens when the people you're connected to are close friends -- 'strong ties' -- because you care about these people," says co-author Andrew Stephen, assistant professor of business administration at the University of Pittsburgh's business school. And when people feel happier, through a self-esteem boost or however else, they do what academic types call "licensing." That is, they feel they accomplished something, so they "reward themselves with something hedonic and indulgent," Stephen says. In other words, they lose a bit of self-control. "We found that to be the case across a range of self-control contexts -- making healthy vs. less healthy food choices, and how long people persist at challenging tasks before giving up," says Stephen. Stephen and his co-author conducted several studies to measure subjects' self-control after browsing Facebook for five minutes against a control group of subjects who browsed news and entertainment websites. He found that Facebook use correlates to a higher body mass index and higher credit-card debt. "Even after just five minutes of Facebook use, people showed higher levels of self-esteem and a reduction in observable self-control," he says. For instance, in the food-choice experiment, the researchers gave subjects the choice between eating a granola bar (healthy snack) and a chocolate chip cookie (less healthy snack). In another, participants were given word puzzles that were (unknown to them) impossible to solve. "The question was, how long before they give up," says Stephen. By a wide margin, Stephen says, people in the Facebook group had weak self-control. They gave up on the puzzle sooner than the control group and chose the cookie over the granola bar. After controlling for demographic and socioeconomic factors, there was a similar relationship between high-frequency Facebook users and higher body mass index and higher credit-card debt (relative to credit limits), Stephen says. (The study's participants reported their credit scores to the researchers and roughly how much credit-card debt they have each month, along with their credit limit.) For Facebook addicts concerned about their will power, "you don't have to reduce your Facebook usage to mitigate your risk" says Stephen. Knowing is half the battle. Just be aware of the potential impact heavy Facebook browsing may have on your ability to choose between the fruit salad and the Snickers bar. "Just think, I'm going to correct myself and go out of my way to not have that lapse of self-control," Stephen says.