Nikki wrote
>    The Kung San mothers were monitored and discovered  to be nursing their
> babies about 60 times a day, about every 15 minutes for  about 2.5 minutes.
> Their babies thrive.
>    How does this mechanism apply to them?

Research has shown 70% of the variability of fat in milk is due
primarily to two things:
the degree of fullness of the breast and
the time elapsed since the previous feed.

The lower the degree of fullness of milk in the breast the
higher the fat content. Obviously this is relative to how much milk is taken
at any one feed as well as to WHEN the feed occurs (degree of fullness is
"generally" always less in the evenings and highest in the mornings)
Therefore on this basis the hindmilk at the end of a morning feed may in
fact have a lower fat level than the foremilk of a feed taken much later in
the day when the degree of fullness is very low. Some people have
hypothesised that frequent feeds and evening unsettledness in infants
in the first three months  may possibly be an adaptation in Western
cultures where babies want lots of high fat feeds at the end of the
day where feeding frequency and fat intake has been relatively low
during the day, and
in preparation for longer intervals between feeds at night. Another
theory is this may also be the cause of "growth spurt behaviour"
because in actual fact the research has shown that the volume taken by
babies is pretty consistant (from one to six months) even when they
appear to be having "growth spurts"

If  there is a short time between feeds (such as in the Kung San
mothers) the fat has not had much time to adsorb (stick to) to the
duct walls and the fat content remains fairly consistant compared
with when there is a long period between feeds and the foremilk fat
will be relatively low (compared to hind milk) because it has had a
longer time to clump together and adsorb to epithelium.

Women who have lower storage capacities or feed small feeds very
frequently have a more consistent degree of fullness over the period
of the day
(than women who have much larger storage capacities and may feed much
less frequently).  Mothers who feed small feeds more frequently will
have less variation in fat content between feeds but the total fat
recieved over a 24 hour period should remain pretty much the same (the
babies just get it differently (and probably more consistantly) due to
variation in feeding frequency).
I should also add there is significant variation in fat
concentration/24 hours between women. Babies still thrive even at
lower concentrations eg: 30g/L vs 60 g/L (so long as adequate volume
is taken) and this is considered normal variation amongst women.

Cathy Fetherston RM PhD IBCLC
Perth Western Australia

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