Mythbusters: Hindmilk is better than foremilk
This isn't new but sometimes we see too much emphasis placed on foremilk vs hindmilk, so here it is; this was on Lakeshore Medical's facebook page today, authored by pediatrician and IBCLC Jenny Thomas:
What is the problem with this myth? Well, first, it implies there are two kinds of milk. Breastmilk varies in composition by time of day, throughout a feeding, by time of day and by low long a mother has been nursing (toddler milk is not the same a milk made for a 3 week old.) If we are judging by recipe, then there are not just two types of milk.
We also have a problem with definition. What is foremilk? It is the milk present in the breast before a feeding. Before it comes out. But, we typically refer to foremilk as the lower calorie, thirst- quenching milk at the beginning of the feeding. Conversely , hindmilk is the milk left over in the breast after the feeding is complete. In the breast. After the feeding. But again, we usually think of it as the higher calorie, richer milk. And while the fat content may vary, other macronutritients of milk show only slight changes.
The idea that one type is better than the other makes people do crazy things to get to the “better” milk- lactoengineering gone wild with creamatocrits, pumping schedules other manipulations done to make milk “richer” or to reach some other goal. Those manipulations are unnecessary most of the time: the total milk consumed in a 24 hour period determines the infant’s weight gain. The total daily fat consumption does not actually vary.
What we need to realize is that the gradient of the fat content, the fact that it gets higher in fat as the feeding progresses is an artifact of how we feed our babies in this culture. There would be no gradient in the fat content in a feeding if we truly fed our children on cue. Foremilk and hindmilk are concepts that wouldn’t matter if our babies had unlimited access to the breast.
We are “carry” mammals: ones who have, in general, lower total fat content in their milk as compared to other species, who need to eat frequently and are meant to be carried by their mothers to have access to those feedings. Other mammals don’t needs this type of constant contact. “Cache” mammals, like the deer, have high fat content in their milk to sustain their babies for longer times in between feedings. The babies are often hidden in a safe place and the mother comes back to feed them at intervals.
So, as a “carry” mammal, we would be carried by mom, have lots of access to the breast, eat frequently and therefore never really have a change in the fat content in the feeding because the breast would be constantly experiencing milk removal.
So why do we know that hindmilk and has higher fat concentration and try to distinguish between foremilk and hindmilk? We see fat concentration differences when with longer intervals between feedings. That’s how we feed in our culture. If we are feeding every 2-3 hours, then there is a difference in fat content as the feeding progresses. That gradient is an artifact of our feeding techniques.
How does it happen? Maybe the fat globules cluster in the alveoli and only are removed at the end of a feeding (Whittlestone, 1953). Maybe they are stuck in the alveolus only when it is full, so when it is less full, the fat globules can be released (Hytten 1954). Maybe, as Atwood and Hartman suggested, the lactocyte changes shape, from flat to square (and therefore more easily removed) as the milk is removed. But it clearly has something to do with how full the breast is.
Below is my elegant drawing of how this might work. When the breast alveolus is filled with milk, the lactocytes are flatter, allowing for more surface area for the fat globule to stick to them. The fat wants to stay- it is "adsorbed" to the cell wall. As the alveolus empties of milk, the lactocytes change shape, have less area for attachment, and therefore the fat globules detach and get into the milk more easily.
Take home message: the only reason we talk about foremilk and hindmilk is because of the way we feed our babies. We often do not let them have continued access to the breast, therefore go longer in between feedings and create this fat gradient.
Jenny Thomas, MD, MPH, IBCLC, FAAP, FABM
Attwood CS, Hartman PE. Collection of fore and hind milk from the sow and thr changes in milk composition during suckling. J Dairy res, 1992; 59:287-98
Hytten FE. Clinical and chemical studies in human lactation:1. Collection of milk samples. II. Variation in major constituents during feeding. III. Diurnal variation in major constituents in milk. Br. Med J. 1954; 1: 249-55.
Whittlestone W. Variations in the fat content of milk throughout the milking process. J Dairy Res 1953; 20:146-53.