On clinical depression and eating, I've seen a number of bits of information
regarding both whole foods diets and sugar-free diets.  You might try a web
search.

Your friend might benefit from a group that follows the book "Potatoes not
Prozac."  The author suggests a slow shift to no sugars or processed grains
and gives considerable good information about brain chemistry and insulin
production.  Her website is at radiantrecovery.com.  The only odd thing--to
me--about this theory is that this woman prescribes a nightly potato...with
some justification for it in seratonin production, but it seems to me it
would be a useless insulin trigger.  There is a bulletin board full of
people battling depression and getting off meds, and the support might be as
helpful as anything to your friend.  Good luck to her and you both

Lou