Heh, nice.
Well, when you're depressed, your metabolism generally slows down, I believe. Also, those people probably aren't eating as much as they would when they were happy. However, I think it's kinda weird, when I lose the weight, I was eating a large poutine most days of the week, which is FULL of fat (about 3x your daily recommended intake), and has some ridiculous amount of calories in it. I kept eating those at the exact same pace over the few months that I lost the weight in.