You know that friend who’s kind of a bad influence? The one who’s great at convincing you to have one more glass of wine or to split the appetizer platter when you know you should opt for the steamed edamame instead?

That friend could be having a bigger impact on your health than you think.

In a 32-year study published in The New England Journal of Medicine, researchers found that individuals who had one or more close friends who were obese increased their own risk for obesity by 57 percent. Surprisingly, the influence of having an overweight friend was stronger than if a sibling or even a spouse was obese.

But before you go blaming your waistline woes on your friends, you should know that you might be having the same bad influence on them.

A 2013 Gallup poll found that smokers were more than twice as likely as non-smokers to have friends or family members who also smoked and that 46 percent of overweight individuals had friends who were also overweight, compared with just 30 percent of normal-weight individuals.

For the public health community, data like this presents a bit of a chicken-or-egg question: Do our friends influence our behaviors (and vice versa), or do we simply tend to prefer the company of others like ourselves?

According to social psychologists, the answer is: “both.” The evolutionary human tendency to mimic the behavior of one another (in order to fit in with a group, thereby increasing the likelihood of survival) explains the mutual influence that you and your friends have on one another, while the principle of similarity dictates that we naturally form relationships with others like us.

We often forget about the significant influence that others can have on our attitudes about ourselves, but we shouldn’t.

Fortunately, from a healthy habits perspective, the source of this influence doesn’t really matter. If you want to change your habits and improve your health, you can start by seeking out the company of people who already practice those good habits.

Here are four ways choosing the right friends can make you healthier:

Mirroring

We look to others to get visual and behavioral cues about what is considered good or acceptable. If we spend time with people who model a healthy lifestyle and consistently make healthy habit choices, our perspective on what “normal” behavior looks like begins to shift.

Surrounding yourself with healthy people is one of the best ways to put your behavior change effort on autopilot. When negative temptations are removed and, in fact, discouraged, suddenly “fitting in with the crowd” involves a whole different set of behaviors than what you’ve been used to doing. When these interactions are ongoing, those healthy behaviors start to feel like your new norm.

Mentorship

Friends can also be a great source of healthy habit information, especially those who have been practicing the good habits for a long time. When you’re around people like that, steer the conversation toward topics you have questions about.

Find out what tricks and tips they’ve used to keep up their healthy habits. Ask for their opinion on diet or exercise trends. While most people’s opinions and experience don’t constitute expert advice, sometimes what you need most is insight from regular people with busy lives just like yours.

Self-Efficacy

Having even just one important person in your life who will encourage and support you can make a big difference in how you perceive your own chances for success. And perception is everything.

The book Self Efficacy: Thought Control of Action, edited by Ralf Schwarzer, compiles a large body of research that shows self-efficacy, or a person’s belief in their ability to do something, is the greatest predictor of success across a variety of endeavors. We often forget about the significant influence that others can have on our attitudes about ourselves, but we shouldn’t.

Our self-image is, in large part, the result of how we imagine others perceive us. By forming relationships with people who will help build and reinforce positive attitudes, you’ll give yourself a much better chance of sticking with your healthy habits.

Accountability

One of the best things about having close friends is that you can confide in them. Trusting someone enough to tell them that you are trying to change your health habits is a big step. It solidifies that commitment in your own mind, but it also ups the ante for you; once you’ve said you’ll do something, it will be harder for you to get out of doing it.

And a good friend will hold your feet to the fire, checking in with you regularly to see how you’re doing and to help you troubleshoot your way around any obstacles that might pop up.

Of course, you don’t have to ditch your lifelong friends whose habits aren’t quite what you aspire to. Just start spending a little more time with the friends you already have who model good behavior. If there aren’t many of those in your current circle, seek out groups that are doing the kinds of things you’re interested in.

Join a walking group or take a healthy cooking class. Sign up for a group exercise class at your local fitness center or join a gardening club. There are tons of ways to meet others who share your health goals.

And who knows, once you’ve been hanging out with these new friends for awhile, you might become the positive influence on others who are less healthy.