I didn't expect to be "thrilling" LOL

I forgot something for the list.
Some people use SAMe for depression. I had that vacant moment, because I have been using SAMe since 1999 for arthritis, and I still succumbed to my winter depression last year! So I don't really think it works for me that way.
It does make me more alert however (so I don't need caffeine).

SAM is made in the body from B6, folic acid and B12 working on converting homocysteine to SAM. SAM then carries the methyl groups around the body to
repair things and make things (including neurotransmitters).

There is also in the research articles beginning to appear about food/addiction.
This is a stress cycle, and involves cortisol.
This is a really good explanation of it:
http://www.beyondchange-obesity.com/...Addiction.html

Increased stress does lead to depression, and alters neurotransmitters in the brain.
http://bjp.rcpsych.org/cgi/content/full/180/2/99

So I have been thinking about your question yesterday in more global terms.
I understand this cortisol link, because I have that response myself to stress.
I unfortunately learned it from an abusive childhood, and I can't seem to shake it myself.

I hope this helps you understand at least the chemistries, behind it all.
It is really a complex dynamic.