Newborn Weight Gain Speed Related to Obesity

I've read from multiple sources that rapid weight gain in newborns is highly correlated to higher rates of obesity later in life. I'm wondering what other factors might be influencing this relationship.

My exclusively breast fed newborn has gained 7 lbs in the first 2 months (was under 6 lbs at birth). Do I need to be concerned about obesity? Also, should I be trying to slow down his weight gain to reduce the risk? Or is it more that he has the personality of a heavy eater and will likely continue that way?