The study, led by Dr. Craig Garfield of Northwestern University, suggests that new fathers gain between 3 and 5 pounds (with the increase often proportional to height) as they settle into the paternal role.
The cause is pure speculation at this point. Could it be the bodys way of subconsciously empathizing with the physical stress on the mother? Do new dads experience a shift in priorities that makes the gym seem frivolous? Or do guys see fatherhood as an excuse to subsist entirely on Lucky Charms?
As is often the case, more research is needed. The most logical hypothesis, by far, attributes this trend of weight gain to a combination of stress, sleep deprivation, and lack of time for exercise. So to all the young dads out there loosening their belts a bit: Cut yourself some slack.