Recent studies showed that obesity is socially contagious. If you have fat friends you increase your risk of being fat. The reverse is also true.
Thin or fit friends will motivate you, subconsciously or otherwise, to adjust your bodyweight accordingly. Seems the memes that are most
detrimental to your mental and physical health are easiest to catch: religion and obesity. Anyone care to argue for or against this point?

Many other behaviors such as recreational drug use, drinking alcohol, smoking, clubbing, and many other activities seem also to be first undertaken
for the same reasons. We get infected by the idea, some wicked malicious piece of programing that we catch from people we admire or associate with.
Although I am not aware of any formal studies confirming this, I'm sure none of you who smoke and drink, just out of nowhere decided to try it.
First the idea of such activities being "cool" or "adult" was firmly implanted in your head by your peers. Am I not right?