Breastmilk is truly unique, even from mother to mother, or more specifically, from infant to infant. It contains all the above nutrients and immune factors, plus other factors such as enzymes and hormones amongst other benefits. It is tailored to the needs of human infants and cannot be replicated or purchased.

The immunological benefits of breastmilk are achieved in many ways. Firstly the immune cells present in the milk offer passive immunity to the infant while the presence of bifidus factor and lactoferrin in human milk aid immune development as well as being beneficial for the infant’s developing gut. Breastmilk also contains IgA immunoglobulins which are produced in response to the primary pathogens the mother has been exposed to around the time of delivery, which confers a specific benefit to her particular infant who is likely to be exposed to a similar mix of pathogens.

Breastmilk is dynamic in terms of both supply and composition and these vary over the course of the time the mother is feeding her child, in response to the growing child’s changing needs. Or if the particular infant has specific need from the beginning of life, e.g in the case of preterm infants, the breastmilk adapts immediately to respond to that need. The breastmilk of a mother of a preterm infant tends to contain a higher concentration of protein than the milk of mothers of term infants, and the concentration of protein in the milk increases according to the degree of prematurity.

Breastmilk also varies in supply and composition over the course of the day and even over the course of a feed. It has been shown to be higher in fat during the day and evening when compared to morning and night (Kent et al, 2006).

The fat concentration of breastmilk is directly proportional to the level of breast emptiness and increases gradually over the course of a feed.

The fat concentration of breastmilk is directly proportional to the level of breast emptiness and increases gradually over the course of a feed. The milk with the highest fat content therefore usually comes at the end of a feed, with this milk often containing more than double the fat content of milk at the beginning of the feed, so it is key to ensure the mother knows the importance of allowing the baby to drain the milk from the first side as much as possible before switching to the other side to take advantage of the richer milk at the end of the feed. As with most things in breastfeeding however, there are exceptions to this rule and in some feeding patterns, e.g. when the baby returns to feed very quickly after ending the feed prior, the breast may be more empty at the beginning of the feed and as such the milk with the highest fat content may be present at the start of the feed on the same side as previously. As such a thorough feeding history and assessment is key to avoid missing these less common cases.

Some use the terms hindmilk and foremilk to describe this phenomenon but this can be confusing as it does not allude to the gradual nature of the change in milk composition over the course of the whole feed.

For further information on foremilk and hindmilk, see our article on same.


Kent, J. C., Mitoulas, L. R., Cregan, M. D., Ramsay, D. T., Doherty, D. A., & Hartmann, P. E. (2006). Volume and frequency of breastfeedings and fat content of breast milk throughout the day. Pediatrics, 117(3), e387-395.

Kent, J. C. (2007). How breastfeeding works. Journal of Midwifery & Women’s Health, 52(6), 564-570.

Ballard O, Morrow AL. Human Milk Composition: Nutrients and Bioactive Factors. Pediatric Clinics of North America. 2013;60(1):49-74.