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