There is only one thing that makes you fat, and that's eating more than you need, regardless of what's causing you to do it(obesity is the result of a mental issue, in my opinion, it's self destructive behavior resulting from poor coping skills). So no, it's not psychological problems that make you fat, you've made yourself fat because of psychological issues. This is what I've seen to be the case in most instances, and it really does seem to walk a fine line. It's not a good enough excuse though, short of very rare disease, there is no excuse to reach the size most hamplanets have achieved.