Foremilk and Hindmilk: In Quest of an Elusive Arbitrary Switch.

**LimeSlice** · May 19th, 2011, 09:09 PM

This a really interesting answer to what I think can be a very confused and confusing aspect of breastfeeding - the foremilk/hindmilk concept.

The funny-shaped woman: Foremilk and Hindmilk: In Quest of an Elusive Arbitrary Switch.

Foremilk and Hindmilk: In Quest of an Elusive Arbitrary Switch.
Over the course of her breastfeeding journey, it is almost inevitable that a mother will encounter the terms "foremilk" and "hindmilk". There is certainly no shortage of confusing and conflicting advice on the concept, which has led to a lot of misunderstanding.

What do the terms "foremilk" and "hindmilk" mean?

In The Breastfeeding Answer Book, "foremilk" and "hindmilk" were defined as follows:
"Foremilk" is the milk the baby receives when he begins breastfeeding, which is high in volume but low in fat (1).
"Hindmilk" is the milk near the end of the feeding, which is low in volume but high in fat (1).
Actually, the terms "foremilk" and "hindmilk" only really refer to samples of breastmilk taken right at the beginning of a feed ("foremilk") and samples of breastmilk taken right at the end of a feed ("hindmilk"). Even then, the advantage of using these terms is debatable.

Why?

A photo on Wikipedia "helpfully" shows two 25ml samples of human breastmilk: "foremilk" on the left and "hindmilk" on the right:

The problem with showing a sample of breastmilk from the start of a feed together with a sample of breastmilk from the end of a feed is that it tells us nothing about what happens to the breastmilk in between the two samples. Mothers end up mistakenly believing that their breasts make two different types of milk, and wonder how long they must feed for before the "foremilk" magically switches over into "hindmilk" (2).

So if the terms "foremilk" and "hindmilk" are misleading and there's no "magic switch" from one to the other, what really happens?

Since The Breastfeeding Answer Book was published in 2003, research in human lactation has advanced (2), so we now understand more about how breastmilk is produced:

Your breasts make just ONE type of milk

There is no magic switch between two different types of milk over the course of a feed. In fact, there is no sharp distinction between breastmilk at the start of a feed and breastmilk at the end of a feed (3). "Milk does indeed change consistency during a feed - but this happens gradually rather than suddenly" (4).

Why does the consistency of breastmilk change over the course of a feed?

The answer lies in what happens to the fat in breastmilk when breastmilk is
produced:
Your breasts are continuously making just one type of milk, containing 'sticky' fat globules that tend to stick to each other and to the milk ducts in the breast as breastmilk is produced (2,3,5).
stored in the breast:
Breastmilk produced between feeds moves down towards the nipple and collects in the breast, leaving increasing amounts of fat globules 'stuck' together further up the milk ducts (3).
and emptied from the breast:
When let-down occurs, the milk ducts dilate (5) and the milk is ejected from the breast. The milk removed at the beginning of a feed may be lower in fat because the fat globules are still 'stuck' further up in the milk ducts (6). As the feed progresses, multiple milk ejections occur (5) and the breast is emptied, more and more fat globules become dislodged and the breastmilk increases in fat (3,6). This has the overall effect of a gradual increase in fat content of breastmilk in each breast independently as milk is removed.

Have a read of the link, it is really interesting, but I haven't copied it all as much of it uses pictures and graphs.