The amazing science of breast milk

Breast milk has been shown to be an ideal source of nutrition for babies, with many benefits for their developing brains, immune systems and digestive tracts.

Breast milk is considered the top choice for a baby’s first food (the World Health Organization recommends that infants should be exclusively breastfed for the first six month of life. It mainly consists of water, fat, protein, as well as vitamins, digestive enzymes and hormones. It is rich in maternal antibodies, and has anti infective properties. Breast milk is also a dynamic, adaptable food – it is fattier in the afternoon and evenings than in the morning, for example. It also varies during a feed. When the baby latches onto the breast, the first gush of milk, or foremilk, is thin and high in lactose, making it thirst-quenching and easy to drink. The so-called hand milk that follows is creamier and fattier, making it more filling. This dynamic aspect is one reason why breast milk is hard to replicate, despite considerable advances in the quality of infant formula.

“Human milk varies over the course of lactation, over the course of a day, from the start to the end of the feed, and to some extent on maternal factors such as her diet,” says Mary Fewtrell, a professor of paediatric nutrition at University College London. Fewtrell highlights non-nutrient ingredients in breast milk such as hormones, cells (including stem cells), microRNAs (small strands of genetic material), which give it unique properties. “We still don’t fully understand the role of all these components but… quite probably they allow the mother to transmit information to the infant about her own experiences and the environment, which is why breastfeeding is sometimes described as ‘personalised nutrition’.”

However, while more than 90% of babies in Nigeria are breastfed at the start of their life , according to the Centers for Disease Control and Prevention, that rate falls to 53% at six months. Health authorities have tried to increase that rate, for example by offering more breastfeeding support to mothers. Diagnosing and treating conditions such as tongue-tie in babies can also help. But in the meantime, parents who do use formula may also wish to understand more about it, including what might be done to improve it.

“Whilst human milk is the biological norm for human infants and provides benefits for both mother and infant, some women may be unable to breast-feed or choose not to do so, and some choose to partly breast-feed,” says Fewtrell. “For young infants, the only safe alternative if an infant is not breast-fed (or not fully breast-fed) is an infant formula which is designed to meet the nutritional needs of infants and support normal growth and development.” Flexibility is expected – there’s no “one size fits all” approach to infant nutrition, she says. However, breast milk is a constantly changing fluid so in a way it’s a moving target, with some components still not fully understood, says Fewtrell, the professor of paediatric nutrition at University College London.