I've recently studied a bit about omega-3 fats and baby's brain development, and wrote an article on those on my site athttp://www.007b.com/breastfeeding_intelligence_diet.php
I ran across info also that DHA levels are very low in women with postpartum depression.
DHA is a non-essential omega-3 fat for adults, it's abundant in the brain. The baby pulls a lot of DHA out of the mother during pregnancy and breastfeeding because it's needed for brain development.
Your body makes DHA (that's why it's non-essential) from the essential omega-3 fat ALA, which is found in flax and hemp.
But the conversion from ALA to DHA is sometimes not efficient, like if your diet has too much omega-6 fats (which standard American diet certainly does) or is lacking in some basic vitamins/minerals.
You can get DHA directly by eating oily fish, like sardines, herring, salmon, and mackerel. However, they advice against eating mackerel because mercury levels might be high in it. Smaller fish that do not live long are safer, like sardines. And I think salmon was OK too.
Or you can take fish oil supplements. however, the leading expert on fats, Udo Erasmus, says that these are sometimes contaminated, and are refined which may affect the quality of oils. I don't know, maybe someone knows a good reliable quality source of fish oil supplements. But if the fish oil smells 'fishy' then it's rancid. Fresh fish does not smell 'fishy'.
And it's probably very advisable to stay away from trans fats, at least for the reason that they can end up in your baby's brain instead of the right omega-3 fats (they also cause heart disease). They are shaped differently than the normal fats and affect how well brain cells communicate. Trans fats are found abundantly in margarine and hydrogenated vegetable oils, AND are formed also if you fry anything in vegetable oil. Use butter/lard/coconut oil/palm kernel oil for frying - saturated fats can withstand heating without this change to trans fats.
well, maybe everyone already knew this, I don't know. Just wanted to post in case it helps someone.