Are Your Friends a Fat Influence?

Research shows that your ability to lose weight now hinges on who you hang out with.

Chances are, you've dined with a friend and had a scenario like this unfold: You start salivating over the idea of ordering linguine carbonara, but tell yourself, Oh, I really shouldn't. Then your friend requests that very dish before snapping the menu shut and handing it to the waiter. "Make it two," you say. And there goes your diet.

Friends' health decisions have a funny way of rubbing off on us. So important is their power that the World Health Organization lists them as a determinant of health, as big a factor as genetics and income level. In fact, understanding how pals shape one another's health behavior has top billing in Healthy People 2010, the government's plan for improving national well-being.

Research has found that smoking, deciding to get the flu shot, and taking vitamins are all socially contagious behaviors. But where our friends have perhaps the most influence is on how much we eat, drink, and exercise.

The (Fudge) Ripple Effect

Having a buddy who packs on pounds makes you 57 percent more likely to do so yourself, according to the key findings of James Fowler, Ph.D., a professor at the University of California at San Diego, and Nicholas Christakis, M.D., Ph.D., a sociology professor at Harvard, who have studied social networks for 10 years. "Consciously or unconsciously, people look to others when deciding what and how much to eat, and how much weight is too much," says Fowler.

So while you weren't planning to even glance at the dessert menu, you might change your mind when everyone else orders brownie sundaes. In some cases, we may even seek out relationships that allow us to indulge, says Susan Bowerman, R.D., of UCLA's Center for Human Nutrition. "Many women have 'food friends' they can call up to say, 'I had a lousy day and some fried mozzarella sticks sure would make me feel better.'"

Your social circle influences your drinking habits too. Alcohol is a notorious diet buster (if you can resist a nacho after a margarita, bless you), and according to University of Pennsylvania researchers, drinking is among the "risk behaviors" that they found study participants were twice as likely to engage in if their friends did.

Part of the reason we're so easily swayed may be hardwired. Gregory Berns, M.D., Ph.D., a professor of psychiatry and economics at Emory University, found that when others influence us, the area of our brain that makes conscious decisions is not activated. Instead, the occipital lobe, where vision originates, lights up. Translation: We focus on what we see other people doing (like biting into a cupcake), not what we know is right for ourselves (biting into an apple).

Unhealthy Competition

Copycatting isn't always bad for your waistline. Research has found that you are just as likely to pick up good habits from pals. If everyone is ordering salad, do you want to be the one to splurge on a burger and fries? Same goes for booze. "We want to behave appropriately, to make a good impression on others," says Patricia Pliner, Ph.D., professor at the University of Toronto at Mississauga.

Sounds admirable, right? Well, there's often a subtext in these civilized dinner scenes. When two girlfriends are competitive with each other—over guys, work, grades—it can manifest at the table. Undereating is a form of one-upmanship. In her study, Pliner found that when women competed against each other in a variety of skills, those who thought they were losing chose lighter entrees than their rivals at lunchtime. "It was their way of winning," Pliner says. In another study, researchers found that even after being literally starved for more than 24 hours, women would consume only as much food (in some cases, as little as 300 calories) as their companions did.

Things can get especially ugly when friends try to sabotage each other—for instance, pressuring a dieting pal to go ahead and order those French fries or skip the gym. "We don't want to be reminded of our own struggles with weight by watching a healthy eater make careful choices," Bowerman says. "We want her to join our club."

Set Your Own Agenda

Hanging with a calorie-conscious crew may keep you on the slim side, but what happens when you join a new club, move to a new town, or start a new job and begin socializing with a new group—one that eats fruit only if it's in a pie? Hint: You'll need to buy some new jeans. That's why it's important to get into the habit of making your own decisions about food. "Being aware of how others influence us is an important first step," says Brent McFerran, Ph.D., an assistant professor of marketing at the University of British Columbia. "If you recognize where you're likely to follow the crowd, you can correct your course." He recommends pre-committing to your meal when you can: Bring your lunch to work, or if you're eating out, be the one who orders first. You'll find that a little independence will keep you healthier and happier in the long run.

By Courtney Rubin