Science is only beginning to unravel some of the complexities of human milk. While we don’t fully understand everything about breastmilk, there are reasons why breastmilk is the way it is.
It isn’t an accident.
Breastmilk is a dynamic substance. It changes depending on the age and needs of a baby.
Substances in breastmilk even vary between mothers – possibly even depending on whether her baby is a boy or a girl.
But, what do these things mean for you and your baby?
Read on to find out.
Breastmilk Variation Depending On Baby's Sex
Katie Hinde, PhD, (an evolutionary biologist at Harvard University) has been researching about how breastmilk may shape a baby’s immunological, neurobiological, and behavioural development.
Her research has found that cows and monkeys make different milk depending on whether the mother’s baby is a boy or girl. For example, her research has found that mothers of:
- Daughters produce more calcium in their milk
- Sons produce milk with higher fat and protein, but lower sugar concentrations
- Daughters produced higher milk volumes, especially if they had reproduced before
Hinde has hypothesised that the following may influence a mother’s breasts to make different milk depending on the sex of her baby:
- A mother interacting differently with her baby depending on whether the baby is a boy or girl
- The pattern of breastfeeding sons may be different to breastfeeding daughters and this can change the composition of a her milk
- Hormonal signals from the developing foetus may influence the breast to affect the milk produced when her baby is born
Since Hinde’s research is not on humans, its significance, if any, to humans is unknown.
We may not know for sure if human breastmilk changes based on the baby's sex, but we do know that it is ever changing to meet the needs of each breastfed baby. Breastmilk varies from mother to mother and even feed to feed.
Here are some other things that impact breastmilk composition:
Genetic Material And Breastfeeding
Again, it’s not up to science to prove the importance of having various factors in human milk. If it is there, it’s most likely there for an important biological reason. However, it makes for interesting research.
A Mother’s Diet
The amount of various substances in breastmilk alters somewhat depending on the mother’s diet. For example:
- The types of fats a mother eats has some effect on the types of fats in her breastmilk. For example if she eats more long-chain polyunsaturated fatty acids (e.g. omega 3 fatty acids), more will appear in her breastmilk
- A mother’s diet can affect the concentration of iodine in her breastmilk
- A mother’s diet can affect the concentration of vitamins in her breastmilk.
However, the average Australian diet typically supplies mothers with adequate amounts of most vitamins.
See our article about poor diets and breastfeeding. For more information about diet and breastfeeding, see here.
Flavours Of Breastmilk
Different flavours pass through to a mother’s breastmilk from her diet. If you’d like your baby to like eating vegetables, it may be helpful for you to do so yourself!
Some research suggests that exclusively breastfeeding for 6 months may make children less picky eaters in early childhood.
Bacteria In Breastmilk
Bacteria travels from a mother’s gut into her breastmilk, and then via her breastmilk into her baby’s digestive system.
The diversity and prevalence of oligosaccharides (prebiotics) and bacteria varies in the breastmilk of different mothers. The source of this variation and the result of it for individual babies are not currently known.
For example, research has found that breastmilk from obese mothers tends to contain a different and less diverse bacterial community compared with breastmilk from healthy-weight mothers.
This research also found that breastmilk from mothers who had a planned c-section contained a different bacterial community than the breastmilk from mothers giving birth vaginally or who had an emergency c-section (i.e. who had some labour before surgery). This suggests that it's not the operation per se but rather the absence of physiological stress or hormonal signals that could influence the bacterial transmission process to a mother’s breastmilk.
Ever Changing Nature Of Breastmilk
A mother’s breastmilk is made as required to suit her baby. For example, the breastmilk made by a mother of a premature baby has different concentrations of various factors to suit her baby’s special needs.
Also, when weaning, a mother's breastmilk increases the concentration of immune protective factors to give her baby a final dose of immune protection before weaning is complete.
What Does This Mean For Donor Milk?
Due to the variations in the breastmilk between individual mothers, what does this say about the use of donor milk or wet-nursing? Well, it may mean different things for different people, based on their cultural backgrounds for example.
However, it is important to remember that human milk is specific for the human species. No formula is specific to humans – most are based on milk from cows.
Breastmilk Is Important
Our health is not just about the absence of disease. It is about optimising our health, performance and recovery throughout our lives.
Science doesn’t have to prove the importance of human milk. This is because human milk is the normal milk for babies of our species. It has evolved and been used to sustain us over millennia and to help us reach our full biological potential.
Human milk is not just food. According to Dr Stephen Buescher (an infectious disease specialist) human milk, “is a highly specialised infant support system.”