We used to think that breast milk was just a food and that it
was filled with fats and proteins and vitamins and that formula
companies were successfully able to mimic this. But we now know
that there are substances in breast milk that exist almost at
the same levels that are not digestible by infants. So what are
they doing there? It turns out, they’re digestible by beneficial
bacteria. So over millions of years, the mother has been
creating a substance that will recruit useful bacteria into her
infant’s gut and this sets her infant up for life. So as much as
breast milk is a food, we also now understand that it’s also a
medicine. — Florence Williams on the benefits of breast milk