If you're worried about your weight, you might consider being worried about your friends, too.
A study published by the New England Journal of Medicine in 2007 cites mounting evidence that obesity, like many other health issues, can spread between members of closely connected familial and friend groups.
"You are what you eat isn't the end of the story," study co-author James Fowler told TIME. "You are what you and your friends eat."
Nicholas Christakis, Fowler and researchers from Harvard and the University of California, San Diego, looked at 12,067 people who were considered "densely interconnected" and followed the way obesity spread for 32 years. From their observation, they learned that a person was 57 percent more likely to become obese if their friend had also become obese.
Even more, when a pair of people both described the other as a "close friend," if one became obese the other had 171 percent greater chance of following in their footsteps.
Interestingly, the researchers found that a friend's weight had a more profound effect on someone than a spouse. The reasons for that are tricky, according to researchers, but they believe that it's a reflection of social norms and who we look at in order to judge what's acceptable for us.
"Your spouse may not be the person you look to when you're deciding what kind of body image is appropriate, how much to eat or how much to exercise," Fowler told TIME. "We get to choose our friends. We don't get to choose our families."
But the murky results have raised some red flags and questions.
Like any study, this one in particular is not bullet proof.
Science has also shown that people are born with a pre-determined weight range of 30 pounds based on genetics. That leaves a lot of room for one's environment to change the way a person gains weight, but it might not be all about your friends.
In a follow-up 2015 study by Ethan Cohen-Cole and Jason M. Fletcher, the pair tried to replicate the results of Christakis and Fowler's study using the guidelines they set out. Unfortunately (or fortunately), they had trouble replicating the results, which typically raises a lot of questions from the scientific community:
We replicate the NEJM results using their specification and a complementary dataset. We find that point estimates of the "social network effect" are reduced and become statistically indistinguishable from zero once standard econometric techniques are implemented. We further note the presence of estimation bias resulting from use of an incorrectly specified dynamic model.
Regardless of the underlying causes, one thing is for certain: the United States has an obesity issue that desperately needs to be addressed. Most recent poll results and studies find that it is a full-blown epidemic, with nearly two-thirds of all Americans either obese or overweight.
"Mississippi had the highest incidence of obesity in the nation for the second year in a row, at 35.2 percent," Gallup said in a statement. "Hawaii had the lowest incidence of obesity in 2014, making it the only state where fewer than one in five residents are obese."
Obesity isn't just about physical health, either. While surveying more than 150,000 Americans, Gallup and Healthways (a consultancy firm) found that "even when factoring in education, religion, age and income, obese adults are 29 percent more likely to say they lack purpose in life and nearly 34 percent more likely to suffer financially than non-obese adults."
For information about how to combat obesity, check out The Children Obesity Foundation.