A 2017 review of literature noted that human milk complexity is generated by “individual variations in breast milk composition, which are attributed to the stage of lactation, the degree of breast fullness, infant feeding, the health of the breastfeeding dyad, and other factors” [1]. That means it’s quite literally always changing, in response to all sorts of different factors. Practically, it also means that the milk a mom makes at 2pm on a Tuesday is constitutionally different from the milk she might make 24 hours, 2 weeks, or 6 months later.
What’s more, the breastmilk a mom makes when her child is sick has more infection-fighting cells than when her child is well. And these changes and adaptations in breastmilk composition continue for as long as the mother breastfeeds. Likewise, breastfeeding remains a vital source of nutrition and immune protection for as long as breastfeeding continues; yes, even after the child is primarily consuming solids!
Even more fascinating, milk composition follows a circadian rhythm and has more sleep-inducing hormones (primarily melatonin) at night time. And the balance of fat and sugar is always in flux, too. When breasts are very full (like they are upon waking when baby blessedly sleeps a bit longer at night!), milk contains more sugar and less fat, while “emptier” breasts (e.g., towards the end of a good, long feeding) make milk higher in fat content. (This is one of the very reasons that in my work as a lactation consultant, I often tell moms that their breasts are rarely, if ever, empty—even when they feel like they are!)
