Natalie Shenker

Out of frustration after a distressing conversation with the mother of a late preterm baby who had been seeking donor milk for her baby on the neonatal unit while she was struggling to increase her milk supply, I wrote the following as an appeal to healthcare professionals to find out more about donor milk, and the science underpinning its use as a supplement to support maternal breastfeeding.

“If I could have a penny… for every time a healthcare professional says, “donor milk has no calories, it’s just water.”

Let’s pick through the facts – donor milk is milk that has been collected from screened milk donors, mothers with extra milk than their babies need. To become a donor to the Hearts Milk Bank, all donors undergo a long process, including checking that their baby is growing well. Donor milk is heat treated, pasteurised, as part of the safety precautions milk banks around the world take. Holder pasteurisation heats milk to 62.5°C, destroying viruses, bacteria and some components of human milk, such as the immune cells. The water content of unpasteurised human milk is 88%. This does not increase after pasteurisation. Calorie content of unpasteurised human milk is around 77 kcal/100 ml (on average, and this is very variable). For donor milk it is 70 kcal/100 ml (on average, and this is very variable). For preterm babies, their metabolic rate can mean that even mother’s milk needs additional energy for babies to grow, but this is controversial between different units and even individual consultants preferring different feed regimes. Donor milk is also fortified in some units (but not in others), and outcomes don’t seem to be different at 2 years. But donor milk isn’t water, or indeed insubstantial nutritionally. Milk banks in many places around the world routinely feed full term babies with pasteurised donor milk. You can see the growth curves for example in this paper by Reimers et al., from their experience with feeding full term orphans with HIV or other illnesses in South Africa. They all grow.

Donor milk contains human milk proteins, human antibodies, human-specific antimicrobial factors, human hormones, human fatty acids, you get the point. The pasteurisation process enhances the anti-inflammatory nature of human milk, diminishing the activity of pro-inflammatory factors, such as TNFα and IFNγ, and leaving IL-10, an anti-inflammatory cytokine, intact. Human milk also contains over 100 different oligosaccharides, short chain sugars, some of which are anti-inflammatory and others support the development of the normal infant gut microbiome. HMOs remain intact after pasteurisation. The function of lactoferrin and lysozyme, both bacteriostatic factors in human milk, is largely preserved too.

As a result of these factors and more, the use of donor milk does not cause an inflammatory reaction in the gut of babies, unlike infant formula. Three Cochrane reviews have demonstrated that donor milk use when maternal milk is insufficient helps to protect preterm and older babies from necrotising enterocolitis (NEC), a devastating disease that kills hundreds of babies each year in the UK. Perhaps even more importantly, when used in the context of optimal lactation support, using donor milk as a supplement can markedly improve the mother’s chance of establishing her own feeds, even at 6 months, which will ultimately provide the optimal health and developmental outcomes for both babies and mothers.

But parents who receive the message from healthcare professionals that donor milk is ‘water’, or even worse “dishwater” as was remarkably said during a dietician’s regional training meeting just last year, get a very different perspective on the value placed by healthcare teams on human milk. Such words, while also factually incorrect and insulting to the thousands of milk donors who give up their time each year, demean the importance of human milk for the health and normal development of babies.

As a final point, but it needs to be made, nobody ever tells parents in the same breath as calling donor milk water not to feed infant formula or cow’s milk, even though they are ultra-processed products, with pasteurised cow (usually) milk, freeze-dried, supplemented with algal, fungal and palm oils to be nutritionally adequate, and undergo other processing steps. There needs to be a fundamental shift in medical and nursing education that includes the science of nutrition, but without the influence of industry funding that has subverted so many of our perceptions.

So please, can we stop telling parents donor milk is water. It is not true. Donor milk will never be mother’s milk – it wasn’t created specifically for their baby. We are working with a range of scientists and clinicians to understand human milk composition and personalise donor milk as a therapy, but right now we know for sure donor milk isn’t water. It is made for humans.

Natalie Shenker, UKRI Future Leaders Fellow, Imperial College London; Co-Founder, Hearts Milk Bank, Human Milk Foundation

If you would like to contact Natalie to discuss medical education opportunities in the science of human milk and breastfeeding, please email

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