Went to class reunion this weekend. So many people had gained so much weight over the past year and they were thin most their lives what is happening?

Food is everywhere. And it's inexpensive. As a species we haven't adapted to the easy availability of food. We're programmed to eat as much as we can today in case there's a famine tomorrow. The trouble is that the famine never comes. Combine that with the fact that our metabolism slows down as we age and we tend to be less physically active, the result is weight gain.