Other reasons might be winter depression (which often leads to weigh gain and overeating). December has the shortest days of the year, and no one wants to go out in the cold weather. Without the sunlight we are not receiving the ultra violet rays that help our bodies produce vitamin D (which is a large cause of depression also a major reason why we get the flu season at the same time every year - when we start staying indoors).
So lets all make an effort to make time to exercise this December so our new years resolution is not to get into the same shape we where in November!
I love my Job!