I have been thinking on this since having written a post.

I knew a guy who's illness was like right smack in the middle of BPI and BPII.

When he would become "manic," he would lose tons of weight, even though he was eating very large amounts of food constantly. It appears the course of illness had changed his metabolism. When he is depressed, he gains a lot of weight, even without a med which causes weight gain.

Thus, it appears as though his metabolism is affected by his mood.