When milk is made, the protein, sugars, water are all secreted into the 
lumen outside the cluster of milk making cells as they are produced. But 
the fat gathers into a milk fat globule, which becomes bound by a 
membrane and makes its' way to the top of the cell (the lumen side) 
where it waits until the MER. When the MER happens, the fat globule and 
some additional membrane is squeezed off the surface of the cell and 
enters the lumen to mix with the low fat milk that is already there.

During a feeding, there are multiple milk ejections. Each one pushes 
some more fat off some more lactocytes, increasing the fat concentration 
of the milk. Since the baby is also drinking the milk that is in the 
front of the breast, the fat content of the milk keeps increasing with 
each MER.

Now, when the feeding ends things get really complicated. The unconsumed 
milk travels back up the ducts, so the milk making cells can sense how 
much got taken (by the pressure the milk exerts). We don't think the fat 
goes back into the cells. We're not sure what happens to it.

If the baby nurses again soon, the milk will be higher in fat. If it is 
a longer time, the breast will again dilute the fat that is already in 
the ducts from the previous MER by continuing to secrete all the other 
milk components into the lumen.

Make sense now?

Catherine Watson Genna BS, IBCLC  NYC  cwgenna.com


On 2/24/2011 5:03 PM, Rosemary McNaughton wrote:
> Maybe someone here can explain this to me, then.  My understanding is that
> breasts make one kind of milk, then the longer it sits in the breasts, the
> more the fat separates and clings to duct walls.  Then when baby goes to
> feed, he gets drowned in the lower-fat milk and fills up volume-wise before
> much of the fat washes down.  Ok, so far, so good - then what about the
> *next* feed - either
>
> 1) baby doesn't wait long to feed again because the feed didn't end up being
> that satisfying, and then gets fresher milk whose fat hasn't separated out,
> plus some of the higher fat milk and unused fat left behind at the last feed
> must wash down now, too, so the imbalance begins to correct.  Or...
>
> 2) baby waits longer to feed again, being overfull from the high volume of
> the lower-fat milk.  In which case the fat from the newly made milk again
> separates out and fat is building up inside the ducts??
>
> Bottom line, I don't see how you can have a sustained imbalance of feeding
> baby "foremilk" - if mom is always making the same kind of milk, where does
> the fat go if not into the baby eventually, no matter what their nursing
> pattern is?  Does mom reabsorb fats through the duct walls?  That would
> explain a lot... but would mean that moms with higher storage capacity
> breasts feed their children lower fat milk overall, and that doesn't make
> much sense either.
>
> I'd appreciate any illumination on this subject - I've asked several more
> experienced people through the years and not been satisfied yet!
>
> -Rosemary McNaughton
> LLLL, NMC Counselor
> Northampton, Massachusetts, USA
>
> On Thu, Feb 24, 2011 at 11:07 AM, Pat Young<[log in to unmask]>  wrote:
>
>> First breast has foremilk and hind milk, 2nd breast has homogenized milk
>> LOL.  Poor gain and frothy green stools with  the hyperlacting mom is
>> usually due to short feeds on each side and baby is drowning in milk. That's
>> why block feeding to tamp down supply seems to work so well.  Whoever
>> thought in 1965 that we would be seeing oversupply problems in 2011?  LOL.
>> Pat in SNJ
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