There is a great deal of confusion among breastfeeding mothers over the issue of foremilk and hindmilk. The names give the impression of two distinctly different types of milk produced by the breast, when this is far from the truth. The breast always produces the same milk, but the fat content of the milk is diluted by water the longer it sits in the breast between feeds. This has the result of offering the baby a faster-flowing water-rich milk that satisfies thirst in the early part of the feeding and a slower-flowing fat-rich milk that satisfies hunger later in the feeding. A more accurate terminology would be dilute milk and concentrated milk.
Discussion of foremilk and hindmilk becomes significant in discussions of feeding duration. Commonly, in order to ensure that mothers get adequate stimulation on both breasts early in breastfeeding, health professionals will sometimes advise timed side switching. While it is important to stimulate milk production on both breasts, it is also important to empty the breasts, and so such advice may work for some women and not for others depending on the efficiency of the baby in emptying the breasts.
When women switch breasts prematurely and/or wait long periods between feedings, allowing the breasts to fill, babies can “fill up” primarily on the more dilute milk in each breast without ever allowing the milk to transition towards higher fat content. Some mothers then report green, frothy stools and irritability in their babies which is sometimes described as foremilk-hindmilk imbalance. Weight gain can also occasionally slow if the baby does access enough more concentrated milk.
It is important to remember that there is no “switch point” between dilute and concentrated milk – the milk slowly becomes more concentrated in fat throughout the feed. See the excellent link I am included below which shows visual images of 12 samples taken over the course of a feed to illustrate this point.
Increasingly, lactation professionals recommend nursing on one side until the baby naturally releases, then offering the other side. Also, nursing on cue, which generally means shorter duration between feeds for most babies, means that milk has less time to become dilute. However, early breastfeeding patterns can be complicated and neither advice fits all mothers or babies. General awareness of finding balance between getting enough stimulation on each breast and allowing the baby to nurse to satisfaction on each breast is important, but specific times and patterns will differ between women.
Link to images of milk fat content throughout a feed:
The Funny Shaped Woman Blog