I believe Kay Motil, who is a nutrition researcher at the large USDA lab in
Houston, did a study once on protein requirements of nursing moms and found
that protein requirements were higher than we thought, and that most nursing
moms were prob. not getting enough protein.  I see some moms who are
struggling with low supply and even mild PPD who also report intense sugar
cravings.  I explore their diets and discover that they are eating poorly,
with diets high in carbohydrates but low in protein.  I think the sugar
cravings result from being energy deficient.  I generally suggest they begin
eating protein at every meal, and the sugar cravings decrease, energy
improves, and often the milk supply increases.  Just because women can make
milk on subsistence diets doesn't mean this is the optimal way to do things.
We know that if you don't feed a nursing animal well, her coat and other
physical characteristics tell you that she is not faring as well as her
pups, kittens, etc.

Barbara Wilson-Clay, BSEd, IBCLC
Austin Lactation Associates, Austin, Texas
http://www.jump.net/~bwc/lactnews.html