The miracle of a mother’s “bespoke” breast milk

Breast milk is more than just a food source for babies. It’s a complex nutrient and chemical “cocktail” that a mother’s body customises just for her little one – and no two are the same.

By David Cameron-Smith

The benefits of breastfeeding have long been extolled by medical professionals, and for good reason. Breast milk has an almost perfect combination of vitamins, fat and protein, is packed with antibodies, and is more easily digested by infants than formula. But what we’ve discovered through our research is that a mother and her baby together shape the exact composition of breast milk – and there is no such thing as a one-size-fits-all breast milk formula.

Together with researchers from the Liggins Institute (University of Auckland, New Zealand), we’ve had the opportunity to measure the appetite hormones found in samples of breast milk gifted by 501 mothers (when their babies were around three months old) from the STEPS (Steps to the healthy development) cohort, a study that analysed the health and growth of 1,797 Finnish mothers and their 1,827 children over four years. Milk samples were airfreighted from Finland to a specialist laboratory in New Zealand, where cutting edge analysis techniques were used to analyse just a few of the many hormones in breast milk.

A complex concoction
The team looked at whether a mother’s health, birth events and the baby’s gender influenced the levels of appetite hormones (leptin, adiponectin, insulin-like growth factor-1 and cyclic glycine-proline). What we discovered was that there are distinct differences when you take into consideration a mother’s weight, measures of a mother’s overall health, whether the birth was natural or caesarean, and the sex of the baby. 

The differences were complex, but we found that the milk of overweight mothers who gave birth to boys by caesarean section differed remarkably from healthy weight mothers who gave birth to girls by natural birth. For all the measured appetite hormones, the mother’s health, how the babies were born and whether a baby was male or female collectively “tweaked” the composition of breast milk.

Dream team
We don’t yet know what these differences translate to for the health of the infant, as the exact functions of these appetite hormones in breast milk are unknown. It’s also not clear if a baby is able to absorb these hormones, and if they do whether the levels in breast milk are high enough to alter a baby’s physiology or brain function. But what this research does show is that mother and baby are a “team” that fine-tunes exactly what each child receives. No two mothers produce the same breast milk.

The big story in breast milk research is its incredible chemical complexity. Breast milk is bountiful in all sorts of hormones, peptides and interesting signalling compounds – the functions of which mostly remain a mystery. However, nature rarely does things without sound reason. All this complexity is a reminder of just how special breast milk is and the wonderful biology that links mothers and their little ones.  

*The full scientific publication is available here.

Dr David Cameron-Smith's research work aims to decipher how nutrition regulates genes and the biochemical pathways that are essential for optimal human health. He has led significant clinical trials that have shed light on the role of protein in the diet of the elderly, the differences in metabolic response to differing proteins, and the differences between intolerances to dairy, as compared to lactose intolerance.