Power of Contrast
The people you spend the most time with profoundly impact your life. If they make more money than you, chances are your income will rise. If they make less than you, chances are your income will fall.
It seems to me the same principle holds true with physique. If the people you spend the most time with are health conscious and fit, then you will likely become more fit. But if they are lazy and overweight, then you will likely become lazy and overweight, too.
One exception to this rule: If you are already healthy and fit, you will probably be unaffected by spending a little bit of time with a friend who is the polar opposite of you. In fact, by the power of contrast, it may motivate you to be different.
I’ve found this to be true in my own life. After spending time with someone who is well on their way to achieving an overfed, middle-aged suburban physique, I feel motivated to act and behave differently so I don’t wind up in the same place.
Ask yourself: Am I spending too much time building wrong relationships? Am I spending too little time nurturing right relationships? (Of course, when you consider these questions, it’s important to weigh many different factors, not just health habits.)