Hi all
I think the factor in cow's milk (and thus presumably in formula) that is soporific
is beta casomorphin - Help! Joy Anderson - you know more about this than me!!
Apparently it is a useful part of cow's and other animals milk in that it keeps
baby quiet whilst mother is out grazing/hunting and so doesn't race around attracting
the local baby-eating animals. It seems to have the same effect on baby humans, although
we are not designed to feed just a few times a day the way that other species are.
As someone else has already mentioned, the tougher curds formed by formula in baby's
stomach are more difficult to digest, thus stomach stays fuller for longer. Unfortunately
I can't remember where we read or heard this (no doubt from Prof Peter Hartmann), but
I've scrabbled through my files and can't find a specific reference. Maybe Joy has one??

Fiona Coombes
Family Physician, IBCLC, NMAA Counsellor