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Two university professors hit the talk-show circuit last year claiming that obesity was contagious. If friends and other members of your social network are overweight and out of shape, they claimed, chances are you may be, too.

In other words, unhealthy behavior may be communicable. Your chances of becoming obese, they said, increase by 57 percent when one of your friends is, 40 percent if it’s one of your siblings, and 37 percent if it’s your spouse.

Intimidating odds. So intimidating, in fact, that they overshadowed the larger conclusion of the professors’ research: Because health and behavior are linked so closely, almost any health state connected to habitual behaviors is communicable.

But here’s the good news: Social connections can also improve your health. After all, people tend to quit smoking in groups. People who hang around others who think positively also tend to think positively. Just as people gain weight together, they also can lose weight together.

According to the 2007 study by Nicholas Christakis, MD, PhD, MPH, of Harvard, and James Fowler, PhD, from the University of California at San Diego, (published in the New England Journal of Medicine), a variety of surprising and seemingly very individual conditions appear able to spread between friends and acquaintances like a juicy rumor.

Even more bizarre, they can skip a link and spread between a person and her friend’s social networks. While “deep” social contacts — the people with whom we are best acquainted or spend most of our time — have the most influence, even a distant acquaintance can have a surprising impact.

For example, if a close friend starts smoking, your chances of doing so increase very significantly, by 36 percent. But even someone who’s three degrees removed from your immediate social circle (a friend of a friend of a friend) can still increase your risk by 11 percent. Weird, but, according to the research, true.

For example, if a close friend starts smoking, your chances of doing so increase very significantly, by 36 percent.

Yet, although less well reported than the “fatness is catching!” message headlining most of the popular media last year, there’s a brighter side to all this social contagion — and it’s the flip side of the very same research coin.

Indeed, what initially prompted Christakis and Fowler’s obesity-is-contagious research was a multidecade heart-health study that showed how social connections could improve people’s health.

In the study, which tracked more than 15,000 men and women in Framingham, Mass., over 50 years, several groups of lifelong friends appeared to have influenced each other to remain shockingly fit well into their 70s.

The lone obese subject in the original group was a man who had moved away (the only one to do so) and appeared to have fallen under the sway of less health-minded peers. The exceptional nature of the man’s poor health led Christakis and Fowler to speculate that both obesity and fitness might be contagious. To date, their hypothesis has proven accurate.

Should the research leave you tempted to ditch your more imperfect acquaintances in favor of an all-or-nothing cadre of exclusively healthy specimens, don’t be too hasty. There’s plenty of evidence showing that simply having friends — even the out-of-shape kind — can help you live a longer, healthier life.

One 2006 study of 3,000 nurses showed that women with 10 or more friends were four times more likely to survive breast cancer, and a 2008 Harvard study suggested that friendship may promote better brain health as we age.

And keep in mind, if you can stick to your own healthy habits and choices, they may well have a winning impact on your social circle over time. “Even as we are being influenced by others, we can influence them, too,” Christakis says.

And keep in mind, if you can stick to your own healthy habits and choices, they may well have a winning impact on your social circle over time. “Even as we are being influenced by others, we can influence them, too,” Christakis says.

Whether or not you’re aware of it, the healthy changes you make to your own life ultimately reverberate through your whole social circle, eventually coming right back to you in the form of increased social support.

And when it comes to creating a health-positive climate in your social circle, Fowler notes that your deliberate choices have good odds in their favor. In the context of the “three degrees of influence” rule, the average person is connected to 1,000 others.

Next time you’re digging deep for a reason to go to the gym, or bike to work, or pack your lunch instead of hitting the drive-thru, this may be a perspective worth keeping in mind. Even if you’re not hugely motivated to make a healthy choice for yourself, you may be just a little more willing to do it for the sake of the people you care about — or even for those you don’t know.

“If you tell somebody they don’t influence anybody, they’re not going to take responsibility for their actions,” says Fowler. “But if you tell them that they influence 1,000 people, I think it changes the way they see the world.”

5 Ways to Stand by Your Healthy Habits

One thing that Christakis and Fowler’s research has made clear is that our capacity to resist negative influences and to sow positive ones is not without limits.

There are times when saying goodbye to certain friends or social contacts is the healthiest choice — most notably when you’re overcoming an addiction, or you know that a particular relationship is having a pronounced negative effect on your health, happiness or personal growth.

In situations like these, cutting loose of heavy anchors and freeing yourself to develop healthier circles of support may be an important step in staying true to your own positive trajectory.

In most cases, however, the positive or negative impact of our social relationships is not quite so cut and dried. Who wants to ditch a good friend just because she has a thing for deep dish pizza? And what about those social contacts we don’t necessarily choose — like sedentary coworkers or negative-minded in-laws?

Though they may pose challenges to your healthy intentions, such less-than-perfect social contacts are not necessarily cause for alarm. In fact, Christakis and Fowler believe that the broader and more varied your social network, the greater its potential benefits for both health and happiness.

Why? Because, although we tend to attribute our happiness to our closest, most significant relationships, the research shows that it’s also fed by regular exposure to small moments of pleasure, novelty and joy — things we stand a better chance of experiencing when we are socially connected and supported by more than just one or two other individuals.

Reaping the fullest possible benefits of your social network while avoiding its pitfalls involves three key areas of skill: First, learning how to recognize when your own behavior is being negatively shaped. Second, developing your ability to deliberately make better choices under pressure. And third, seizing opportunities to gently, patiently nudge your network in healthier directions. Here are five ways to get started:

1. Acknowledge Irrationality

If there were a golden rule of behavioral science, this would be it: We make rational choices less often than we think we do.

This isn’t a failing of character or intelligence, but rather a function of efficiency. Because each one of us is faced with thousands of little decisions daily, no one has time to rationally weigh each and every one, so we fall back on our automatic systems of patterned thinking, habit and the rapid processing of subtle social signals.

You need the automatic system to function, but its efficiency can sometimes backfire — like when you take two doughnuts just because all your coworkers did, and you don’t even like doughnuts.

We’re especially responsive to social and environmental cues when conditions are unfamiliar or socially uncertain, behavioral experts note. This makes business lunches, travel and parties prime breeding grounds for unconscious choices and outside influences.

Because uncertainty makes us more likely to look outside ourselves to see what others are doing, our health commitments become more vulnerable in these situations.

You can retain maximum consciousness by going into unfamiliar environments with an already-laid-out plan. Prior to a business lunch, research the menu online and decide in advance what you’ll order; or decide that you’ll always order more or less the same thing (a green salad and grilled fish, for example).

When traveling, scope out the location of the nearest gym or running track, and pack snacks for the trip so you won’t be tempted by airport food. If you’re heading to a party, decide ahead of time whether you’ll have one drink or two.

When you make and rehearse your choices in calm conditions, they’ll be waiting in your cranial wings during uncertain moments, and you’ll be less likely to resort to following others’ leads.

And that brings up one final suggestion: When you practice healthy behaviors in front of others who may be making different choices, resist the temptation to lecture or nudge them, but also don’t apologize for being weird or boring.

Instead, make your choices with as much nonchalance as you can muster. Since studies show our desire for belonging motivates us to do whatever others are doing — whether it’s healthy or unhealthy — behaving as if your choice is the norm may unconsciously influence your companions to mimic your healthy behavior.

2. Write Your Own Food Policy

The unconscious, cue-primed mind plays an especially prominent role when it comes to how (and how much) we’re likely to eat. Brian Wansink, PhD, has conducted numerous studies at Cornell University that show how readily research subjects overstuff themselves in situations where there are no clear cues telling them when to stop eating.

One study showed subjects consuming multiple quarts of soup from trick bottomless bowls before recognizing that they were full. This experiment suggests that while we might think we stop eating because we’re full, we might actually be much more attuned to external signals  — or the lack of them — than internal ones.

To counter the tendency for mindless eating, Wansink suggests two strategies: food policies and food tradeoffs.

A personal “food policy” is a set of guidelines that you follow so consistently in all food-related situations that they quickly become habit. You might decide to become religious about putting your fork down between bites, or always be a vegan during happy hour — thus deftly avoiding the half-price wings.

With a “food tradeoff,” one choice is steadfastly linked to another: “If I snack in front of the TV, it’s on only raw veggies and hummus,” or, “If I order fries, I also order greens.” This makes good sense nutritionally and socially. The network factor means that the very presence of a salad on the table is a green light for others to order one, now or later.

Finally, if you’re in a situation that feels new or uncomfortable, make it part of your food policy to be the first person to order whenever possible. If there’s no other choice to copy, making a healthy one is that much easier.

3. Build an Exercise Entourage

Most of us know that getting to the gym or going out for a run is a lot easier with a workout buddy, but Christakis and Fowler suggest that one of the best ways to protect your fitness routine from wayward influence is to invite the friends of your friends to work out.

When you and a friend work out together, there’s still a circle of others (including his or her other pals) who might be nudging you both in more sedentary directions. But if you can build an effective “wall of influence” around your friend as well as yourself, your chances of sticking with your fitness routine are even greater — because that friend will now be under positive pressure from more sides.

This can be as simple as inviting a friend and a couple of his friends to join you for a weekly yoga class or pickup basketball game. It’s an easy way to build friendships based on healthy common interests; it also helps you build a team of buddies who are consciously and unconsciously influencing one another to be active. The “wall of influence” approach can also extend easily to other healthy behaviors, like a healthy-cooking club.

4. Keep on the Sunny Side

One reason why most of us feel so good when we’re around cheerful people — and not so great around diehard complainers — is that we unconsciously imitate others’ facial expressions. This response triggers a similar emotional state in the imitator, with a corresponding physiological result.

A 2008 study at the University of Missouri–Columbia showed that friends who reinforce each other’s negative moods by “co-ruminating” actually ramp up each other’s levels of stress hormones, while multiple brain imaging studies show that looking at pictures of happy faces can activate a cascade of positive-feeling chemicals in the brain.

The good news about the contagious nature of emotional states is that they’re skewed in favor of the positive. According to Christakis and Fowler’s research, a friend who’s feeling good improves your chances of happiness by 9 percent, while a discontented one is only 7 percent likely to bring you down. This means that bolstering your own mood also has a disproportionately positive effect on others — many others.

Fowler says that, since he learned that his moods don’t just affect his son, but also “his son’s best friend and his son’s best friend’s mom,” he regularly plays happy music on the way home from work so he’ll be in an upbeat mood when he greets his family.

Similarly, meditation teacher James Baraz’s 10-step “Awakening Joy” program ( encourages participants to sing daily because of the positive correlation between music and mood. Baraz also recommends routinely spending 30 seconds to focus on your gratitude for a particular person or thing at least six times a day. Research shows that regular gratitude practice has the capacity to create new neural pathways that support a more positive outlook. Because others are likely to “catch” your positive feelings even more than your negative ones, this can be an especially generous practice.

By consciously generating your own positive vibes and steering clear of “co-rumination” opportunities, you stand a better chance of lifting both your own happiness and that of your extended social circle.

5. Reprogram Your Brain

Because our powerful inclination to imitate and submit to norms tends to issue from the older, survival-oriented regions of the brain, it can be helpful to consciously engage the more sophisticated neo-cortex whenever you feel a group behavior sucking you in.

Whether you’re being encouraged to order too much greasy food, included in unfriendly gossip, or cajoled into skipping your run and watching Dancing With the Stars instead, you can call on your neo-cortex to help you do the right thing.

Psychiatrist Daniel Siegel, MD, an expert on the relationship between neural circuitry and behavior at the UCLA School of Medicine, explains that whenever you feel threatened — even by something as innocuous as peer pressure or the feeling of being pulled in two directions — your body triggers the fight-or-flight system. In this state of reaction, you lose touch with anything that doesn’t relate to your immediate safety — including your commitment to your long-term health and happiness goals.

The primal mind equates inclusion with survival, so it’s almost always likely to direct you to go along with the crowd. The neo-cortex, on the other hand, is capable of a slightly more fine-tuned understanding of threat: It knows that ordering a salad will put you in no danger, even when everyone else at the table is ordering burgers.

So, how do you give your neo-cortex the upper hand? Siegel suggests two quick techniques: body scanning and labeling.

Body scanning involves doing a quick check-in with your bodily sensations. Noticing a tight gut, a flushed face or shallow breathing allows you to assess that something has tripped your alarm system and that it’s time to step out of the situation. A quick trip to the bathroom, or even a couple of deep breaths may be all it takes to regain your rational state of mind.

Labeling involves identifying your emotional states and giving them a name. Clearly identifying “this is fear” or “this is approval seeking” is often all it takes to kick the reasonable neo-cortex into action. Recovering this neural connection produces enough clarity to keep the brain from being flooded by stress chemicals and leaves you in a better state to make choices you can feel good about.

The other great thing about doing this kind of mental shift, as Siegel explains in his book Mindsight: The New Science of Personal Transformation, is that the shift from reactivity to noticing and receptivity also “turns on our social engagement system.” Inducing a calmer state of awareness allows us to be much more tuned in to others, and to take more authentic interest and pleasure in their company, rather than just fixating on, say, the plate of food in front of us.

“When we can sense our own internal state,” Siegel says, “the fundamental pathway for resonating with others is open as well.” In this situation, everybody wins: We all stay healthier, more conscious and more connected.

This article originally appeared as “A Healthy Kind of Contagious” in the September 2010 issue of Experience Life.

Courtney Helgoe

Courtney Helgoe is the Experience Life features editor.

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