You say "hindmilk," I say "milk"

Lately, I've had a slew of clients who are all concerned about hindmilk (among other things), and I've been wanting to shed some light on this topic. For the most part, my response to someone who inquires about her "hindmilk" situation is, "please forget you ever heard that word, and don't worry about it."

What is hindmilk, exactly? It's really just a fancy word for milk. 

Many years ago, some lactation experts introduced the concepts of hindmilk (the "fattier" milk at that flows from the breast after baby has been suckling for a bit) and foremilk (the "watery" milk that flows from the breast at the start of a feed). And while it's true that slight variations in the fattiness of your milk do occur throughout the day and from the start of the feed to the end of the feed, this isn't really something that most women need to think (much less worry) about whatsoever. 

The scenario that most often comes up in my practice is that I'll be observing a nursing session with a new mom, and notice that baby is hanging out at the first breast, sucking, but no longer actively swallowing the way he/she was at the start of the feed.

And I'll ask the mom, "when do you usually decide to switch baby to the other side?" 
The most common response I'll get is, "well, I want to make sure baby gets alllllll the hindmilk."

A common refrain we hear these days in the lactation world is the advice to "finish the first breast first," before switching sides. Rather than look at a clock and decide to switch sides after some arbitrary number of minutes, the way nursing mothers were advised to do in recent history, mothers are now advised to let baby finish whatever side baby has started on before switching over. The reason to wait, they're told, is because of the hindmilk. 

While it is true that it's best to "finish the first breast first" the reason isn't so much that baby needs every lost drop of "fattier" hindmilk from the first breast as it is that it's best to empty the first breast before switching over ("empty" in this case just means that milk is no longer readily flowing; you will still be able to express some milk from an "empty" breast). The goal is to not leave large quantities of milk sitting in the breast at the end of the nursing session. Milk that sits in the breast for long periods of time is going to lose a bit of fat content before baby returns to the breast to feed again.

I love the analogy that Kelly from Kellymom uses to describe hindmilk and foremilk. She compares the human breast to a water faucet. Because I live in an old, New England, Victorian-era farmhouse, this analogy is quite relevant in my life, and hopefully you can relate to it to. Imagine what happens when you turn on the hot water in a second-story bathroom sink. For the first bit of time, the water that flows from the tap will be cold, while the hot water makes its way up the pipes from the basement. The hot water in this analogy is the hindmilk, and the cold water is the foremilk. If, after washing your hands in the finally-hot water, you turn off the tap for only a few minutes and then return to use the hot water again, you will usually find that the hot water runs quickly. You don't need to wait for it to come up from the basement because the water hasn't had time yet to cool in the pipes. Alternatively, if you leave the bathroom for several hours and then return to wash your hands again, the water that was once hot in the pipes will have cooled down again, and it will take a minute or so of letting the tap run before the water runs hot. 

It works in a very similar way with your milk. If baby nurses frequently from the same breast, the milk will remain relatively "fatty," just as the hot water flows relatively quickly from a tap that is frequently turned on. If milk sits in the breast for a couple of hours (or longer), it will lose some fat content with the passage of time, and the "foremilk" available at the start of the next feed will have lower fat content than the "hindmilk" did at the end of the previous feed. But baby can still get plenty of fat so long as baby drains the breast of milk at the next feed. And just like water in the tap—which tends not to go dramatically from cold to hot, but rather warms gradually as the water flows—the milk gradually increases in fat content as the feed goes on, depending on how quickly it is being removed from the breast. If the faucet is turned on full blast, the hot water will appear faster than if the faucet is only opened up to a trickle. Likewise, when baby nurses actively and eagerly, and removes milk quickly, the milk increases in fat content faster than when baby is being more lackadaisical (and perhaps is nursing less for hunger than for comfort). 

The best way to ensure that your baby is getting all the fattiest milk your body can make is to nurse frequently. The less time that elapses between feeds, the fattier your milk will be (to a point! There is, of course, a limit to how fatty human milk can be; it's a relatively low-fat milk when compared to the milk of other mammals). Nursing frequently is a much better way to ensure that baby gets plenty of fatty milk vs. keeping baby on one breast or another for an extended period of time. 

But when do you switch sides? How do you know when the first breast has been "finished"? Some babies will pop themselves right off of the breast when they've drained it as a way of telling you that they're ready for the other side. But many babies—especially newborn babies—will just keep right on sucking on the first breast, regardless of whether or not milk is continuing to flow. This is why it's important to learn to tell the differences between the various types of nursing and sucking that your baby does. A baby who is actively nursing is sucking relatively continuously (with occasional pauses to rest), and more importantly is swallowing very frequently. During active nursing, your baby will swallow after every suck or every couple of sucks. Once the flow of milk has slowed, baby's rate of sucking may also slow, and baby's rate of swallowing will definitely slow. You'll notice that baby is only swallowing intermittently, after several (10 or more) sucks, or may not be swallowing at all. This is a good moment to switch baby to the other breast, no matter how long baby has been nursing on the first breast for. You can return to the first breast (or "third" breast) after baby has finished swallowing on the second breast. 

Ironically, I've seen quite a few babies who weren't getting quite as much milk as they'd like because they were being restricted to nurse on one side, well beyond when they'd finished swallowing at that breast, due to their parents' concerns about hindmilk. This is why I mostly advise my clients to forget all about "hindmilk" and "foremilk" and think only of the liquid flowing from their breasts as milk