Paula Meier has done some work with measuring fat levels in breast
milk.  You could probably do pre and post feed weights and determine
with relative accuracy the amount of fat in the breast milk by doing a
creamatocrit.  This is done using a hematocrit machine to spin a sample
of milk and determine the percentage of fat in the milk.  However, this
seems like a lot of work for everyone.  We know that breast milk is the
most easily digested food.  Why does it matter how well the baby absorbs
fat if he is getting the best possible food?

Bonnie