I've lost and gained a ton in my life (only half kidding). This article attempts to explain the gain part - a hormone called Lepitin.

Health Journal - WSJ.com

I love this kind of stuff. Thank you!

A while back I had read something about the lap band and how it seems to effect a hormone that helps the body feel full. There's a second hormone that works with Lepitin called Ghrelin. Somehow the band seems to elevate one of these hormones and that helps you to feel satisfied and less likely to have the emotional snack attack. I don't totally understand it because not much is written for the lay person. I do know that they think that these findings may very well lead to a pill for obesity someday.

Another thing I wish I could figure out is why sometimes, and it's almost always at night, I get a maniacal need for food. It's like a crazed drive to find just what my body needs. Very hard to fight through that. I'm guessing it's related to Lepitin.