Just when you thought your breast milk couldn’t be any more amazing, new research has come out suggesting that it self-tailors to the sex of your baby.
Yes, that’s right – baby boys and baby girls get different breast milk.
The study was inspired by previous research that showed some mammals produce milk tailored for the specific sex of their offspring. For example, macaque monkeys produce milk richer in fats and gross energy for their male offspring, but produce greater quantities of milk that is also higher in calcium for their female offspring. There have been similar results in human studies as well.
To see if this theory applied to humans, researchers used data that had been collected by the National Longitudinal Study of Adolescent Health — a large, long-term behavioural and medical study of young Americans. For the study, participants were interviewed at four different times in adolescence.
Researchers looked specifically at the data that had been collected from twins: same-sex twins and opposite-sex twins, both breastfed and non-breastfed. They found that breastfed same-sex twins were taller and heavier through adolescence and early adulthood than breastfed opposite-sex twins who, theoretically, received breast milk that could not be simultaneously tailored for the different sexes.
By contrast, same-sex twins that were never breastfed were shorter and lighter than opposite-sex twins that were not breastfed.
Though this research suggests that there is a sex bias in human breast milk, more research needs to be done to confirm it.