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Some fallacies won't die.

One that has long been debunked but that I still see floating around daily is that human milk must be gently swirled and not shaken. Somehow we developed the idea that our milk is so fragile that shaking would damage the milk components.

Parents care deeply about milk quality and because we are generally cautious by nature when it comes to our babies, the urging to avoid shaking has persisted.

The foremilk/hindmilk misconception, unlike the swirl vs. shake myth, is complex. And unlike the swirl/shake myth, the foremilk/hindmilk myth is based on a misunderstanding of factual information. Because this is a misapprehension of facts held by the general public, it’s doubly hard to clear and dispel.

In this post, I will break down the misconception and hopefully provide some clarity on the matter.

Note: It may sound like semantics but the language we use around lactation matters. Many parents have quit human milk feeding due to concerns that their babies aren’t getting enough “hindmilk”. Similarly, many parents have dumped their “foremilk” because they felt that there was little benefit to the “watery, low-fat milk”. Try to keep that in mind as you continue the post.

Before I begin, I want to ask two quick questions.

What term would you use to describe breast milk in the middle of the feed/pump session, if foremilk is the term used for the milk at the beginning of a feed, and hindmilk is used for milk expressed at the end?

Additionally, assuming that foremilk is the terminology used for breast milk that has little to no fat and hindmilk is used for a lot of fat, what would you call milk that had a moderate amount of fat in it?

The major issue with the foremilk/hindmilk concept in its current state is that as much as we say we don't think of milk as being different "types", creating a label to classify low vs. high-fat content naturally creates a distinction.

For many parents, having distinctions regarding types of breast milk can be very confusing. I see this a lot in conversations about colostrum, where many, instead of thinking of milk on a continuum of composition, think of colostrum as being a separate substance than mature milk.

The way we commonly see the transition of colostrum to mature milk described is a perfect example of this. It's discussed as though one day you have colostrum and the next day your "real" milk will suddenly, magically appear, aka coming in, with little mention to the fact that colostral milk makes a gradual adjustment in nutritional composition spanning the course of a couple of weeks.

A seemingly minor oversimplification of facts can have a massive impact on understanding, and the foremilk/hindmilk misconception is an excellent example of this.

To understand the bigger picture regarding "foremilk" and "hindmilk" it's important first to understand milk synthesis, (aka how milk is made).

Breast Milk Synthesis (an abbreviated explanation)

Though all milk parts are created in the lactocyte (milk-making cell), each component takes a different pathway to be synthesized. Because there are 5 different paths, the components of milk don't come together until they all arrive in the alveoli. I mention this because milk is not one unified liquid per se, rather, it's a mix of different components that are released into the alveoli and ducts in a synchronized manner.

With that said, it's important to note that milk always starts off as concentrated, meaning that the ratio of milk components compared to water volume is high. As time passes and milk remains in the breast, more water and lactose are drawn into the alveoli, changing the concentration.

So what does this mean in respects to the misconceptions regarding foremilk and hindmilk?

Well to start, it means that not all milk that is released at the beginning of a feed is going to be low in fat.

"Low in fat" is a relative phrase and to say that it must be compared to something. Yes, milk released at the beginning of a feed tends to be lower in fat compared to the end of the feed (which I will explain in a moment), but it doesn't mean that it's low in fat.

Interestingly enough, the amount of fat in human milk for one parent at the beginning of a feed can be HIGHER than the fat volume of another parent at the end of their feed.

Also, assuming we continue to use the term foremilk and hindmilk in a day to day setting, it means that that the time it takes to "get through" the foremilk will vary depending on a variety of factors (time since last feed, quality of breast drainage during previous feeding/pumping sessions, the rate of milk production, storage capacity, etc.).

But why is the fat ratio lower at the beginning of a feed compared to the end?

Essentially it comes down to a combination of ductal pressure and the fact that there are aqueous and lipid fractions of human milk.

As I mentioned earlier, milk is not a unified liquid and the characteristics of the aqueous part of the liquid means it flows more easily under high ductal pressure. And if you recall, the fat to water ratio decreases as more time passes between feeds.

The less full your breasts are, the lower the ductal pressure and the less time for the “concentration” of breast milk to become diluted with water (and stuff), thus making the fat ratio of the beginning milk to be HIGHER.

Fuller breasts have higher ductal pressure and have had more time for the water and lactose to increase in volume compared to the volume of fat and so the aqueous (watery components of the milk) flows more easily than the lipid part of the milk.

As ductal pressure reduces over the course of a feed, there is a gradual increase of fats because the less-aqueous fractions of the milk are able to move more freely. Additionally, fats have a tendency to stick together, which may also contribute to the rate that the lipid fractions are released during a feed/pump.

Notice in the description I provided of how milk fat ratios change over time, there’s no room for the terms “foremilk” or “hindmilk”. These aren’t accurate to describe the process or even the composition of milk at any given time.

It would appear that the term “foremilk” was first introduced around 1810 and grew in popularity as the dairy industry, along with the study of cows milk, grew during the mid to late 1800’s. The established term, which was not used in the same way it’s commonly used today in conversation amongst parents, seems to have stuck, is a common term used in the research of human milk.

When studying the biochemistry of human milk, the terms foremilk and hindmilk have significance. On a day to day basis, the terminology is useless.

I am not the first person to try to dispel this misconception. If you want to hear a different explanation of the subject, along with seeing the stats of milk ratios during the course of milk expression, I highly suggest you check out Foremilk and Hindmilk: In Quest of an Elusive Arbitrary Switch written in 2011 by the funny-shaped woman.

One image that sticks out to me is this image, where she has all of her samples lined up, after they’ve separated into layers, where you can see that there is no clear line where “foremilk” ends and “hindmilk” begins. Note: All 12 of these samples are from 1 pump session. Furthermore, each sample separates into layers, which is expected and normal for milk.

You can also check out this post on the subject written by Nancy Morbacher.

What you can do

I’ve learned long ago that having new information doesn’t always quell concerns. The fact that fat volume is truly lower at the very beginning of a feed AND the fact that everyone seems to be talking about the topic from a place of concern means that actionable advice may be warranted.

If you’re concerned about the fat ratios at any given time, here’s two things you can do

1) Massage or compress your breasts during nursing/pumping. The heat from the massage, along with the motion of massaging, may help with getting more of the lipid fraction of your milk “down the pipeline” faster.

2) Feed frequently and drain your breasts thoroughly. You may see this suggestion a lot if you’re a regular reader of my blog but it really does solve almost all of the milk-making related challenges. If your baby doesn’t drain well, seek lactation support as soon as possible, and follow feedings up with a pump session to ensure good drainage.

I will tackle the issue of Lactose Overload (formerly, commonly and incorrectly referred to as foremilk/hindmilk imbalance) in a different post. For the end of this post, I wanted to leave you with a few common questions parents have regarding foremilk/hindmilk that highlight the misunderstanding. Given the latest information you’ve learned, I would love to hear your comments on how you’d answer these questions!

• I just read an article on foremilk and hindmilk. How do you know if your baby has gotten all of it?! The article said to make sure your baby gets the hindmilk before offering the other side. Since your breasts are never truly empty, how do you know if your baby has gotten it all?"

• Foremilk and hindmilk question. I have a 2.5 week old and I pump twice a day. I noticed my pumped milk is more watery looking. Do I need to pump longer for the hindmilk to come through?

• If I’m using my Haakaa on the opposite side when nursing to catch the letdown, is it basically all foremilk that I’m catching and freezing?

• Anyone have to pump and separate your foremilk and hindmilk? What did you do with your foremilk?

• How do I know if my baby is getting enough foremilk and also hindmilk?

• How do I go about fixing a foremilk/hindmilk imbalance? Even after baby nurses for 30+ min and I pump after, it’s still just foremilk. I can’t remember the last time I saw hindmilk and baby girl is not getting full on the foremilk.

• I'm nervous he's only getting the foremilk and not sucking long enough to get the hindmilk. Not sure if the foremilk can make him gassy? Would it help to pump a little bit before he nurses so he is definitely getting the hindmilk?